Hardest Trivia Questions Quiz On USMLE

2.

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

Clavicles
Femurs
Metatarsals
Phalanges
Tibias

Correct Answer

A. Clavicles

Explanation

In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull, and facial and dental anomalies. Note that you could also have answered this question by noting that of the bones listed, only the clavicles form by intramembranous ossification. The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones.

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3.

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

Clavicles
Femurs
Metatarsals
Phalanges
Tibias

Correct Answer

A. Clavicles

Explanation

In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull, and facial and dental anomalies. Note that you could also have answered this question by noting that of the bones listed, only the clavicles form by intramembranous ossification. The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones.

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4.

During embryological development, hematopoiesis occurs in different organs at different times. Which of the following are the correct organs, in the correct sequence, at which hematopoiesis occurs embryologically?

Amnion, yolk sac, placenta, bone marrow
Placenta, liver and spleen, yolk sac, bone marrow
Placenta, spleen and lymphatic organs, bone marrow
Yolk sac, bone marrow, liver and spleen
Yolk sac, liver, spleen and lymphatic organs, bone marrow

Correct Answer

A. Yolk sac, liver, spleen and lymphatic organs, bone marrow

Explanation

By the third week of development, hematopoiesis begins in the blood islands of the yolk sac. Beginning at 1 month of age and continuing until 7 months of age, blood elements are also formed in the liver. Hematopoiesis occurs in the spleen and lymphatic organs between 2 and 4 months, and in the bone marrow after 4 months.

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1

5.

The parents of a 6-month-old child who was normal at birth bring her into the clinic. Since their emigration to the U.S. from Eastern Europe soon after her birth, the child has developed diminished responsiveness , progressive blindness and deafness, and recently, seizures. Serum levels of which of the following compounds would be expected to be decreased in both of the parents?

Dystrophin
Hexosaminidase A
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
Phenylalanine hydroxylase
Vitamin D3

Correct Answer

A. Hexosaminidase A

Explanation

This patient has Tay-Sachs disease, an autosomal recessive disorder caused by the deficiency of hexosaminidase A, which leads to the accumulation of ganglioside GM2 in neurons, producing a degenerative neurologic disease. Children appear normal at birth, but then begin to suffer from diminished responsiveness, deafness, blindness, loss of neurologic function, and seizures. A cherry-red spot on the macula may be seen by ophthalmoscopic examination. Death usually occurs by 4 to 5 years of age. There is no therapy. The incidence is higher among Jews of Eastern European descent. Since the parents must be heterozygotes for the mutant hexosaminidase A allele, they would be expected to have diminished levels of the enzyme. A defect in the dystrophin (choice A) gene produces Duchenne muscular dystrophy, characterized by onset of weakness in early childhood. A severe deficiency in HGPRT (choice C) will lead to Lesch-Nyhan syndrome, characterized by excessive uric acid
production, mental retardation, spasticity, self-mutilation, and aggressive, destructive behavior. Deficiency of phenylalanine hydroxylase (choice D) results in classic phenylketonuria, a disease in which phenylalanine, phenylpyruvate, phenylacetate, and phenyllactate accumulate in plasma and urine. Clinically, there is a musty body odor and mental retardation. Hypophosphatemic rickets is an X-linked dominant condition causing abnormal regulation of vitamin D3 (choice E) metabolism and defects in renal tubular phosphate transport. Symptoms include growth retardation, osteomalacia, and rickets. --------------------

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6.

A 60-year-old male with angina comes to the emergency room with severe chest pain unresponsive to sublingual nitroglycerin. An EKG shows ST segment elevation in the anterolateral leads, and thrombolytic therapy is initiated. If streptokinase is given to this patient, it may produce thrombolysis after binding to which of the following proteins?

Antithrombin III
Fibrin
Plasminogen
Protein C
Thrombomodulin

Correct Answer

A. Plasminogen

Explanation

The fibrinolytic activity of streptokinase is due to its ability to bind and cleave plasminogen, producing plasmin. Plasmin directly cleaves fibrin, both between and within the fibrin polymers, thus breaking up thrombi and potentially restoring blood flow to ischemic cardiac muscle. This same mechanism of fibrinolysis is shared by urokinase and tissue-plasminogen activator (tPA). Antithrombin III (choice A) is a coagulation inhibitor that binds to and inactivates thrombin. Antithrombin III is anticoagulant, not fibrinolyti

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7.

A man presents to a dermatologist because of a severe mucocutaneous rash that involves most of his body, including his palms and soles. Questioning reveals that he is a merchant marine who several months previously had an encounter with a prostitute in Southeast Asia. Which of the following is the most likely causative agent of this rash?

Herpes simplex I
Herpes simplex II
HIV
Neisseria gonorrhoeae
Treponema pallidum

Correct Answer

A. Treponema pallidum

Explanation

The rash described is that of secondary syphilis, caused by Treponema pallidum. Involvement of palms and soles by a rash is unusual, and secondary syphilis should come to mind. Not all patients with secondary syphilis have a severe form of the rash, and consequentially some cases are missed. Primary syphilis takes the form of a painless, button-like mass called chancres. Tertiary syphilis, which is now rare, has a propensity for involving the aorta and central nervous system and can also cause "gummas" (granulomatous-like lesions) in many sites, notably including liver and bone. Herpes simplex I (choice A) usually causes perioral vesicular lesions. Herpes simplex II (choice B) usually causes genital vesicular lesions. HIV (choice C) does not itself cause a rash, although co-infection with other organisms can result in a rash. Neisseria gonorrhoeae (choice D) does not typically cause a rash.

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8.

A 37-year-old woman who was diagnosed with AIDS 3 years earlier is unable to work, is physically debilitated, and requests her physician to provide her with medications with which to take her own life. The most common emotional disorder that results in such requests by patients is

Bipolar I disorder, manic type
Borderline personality disorder
Factitious disorder
Major depressive disorder
Schizophrenic disorder

Correct Answer

A. Major depressive disorder

Explanation

Many people who request physician-assisted suicide have one of two conditions present: either a poorly controlled painful condition or
severe depression. If the painful condition is adequately treated or the depression is brought under good medical control, the request for physician assistance in terminating the situation is typically withdrawn. It is important to note that bringing these conditions under control requires the intervention of caregivers who are specifically trained in the management of these two conditions; primary care physicians usually are not adequately trained to address these difficult presentations. While patients who are diagnosed as bipolar disorder (choice A), borderline personality disorder (choice B), and schizophrenic disorder (choice E) often make suicide attempts (and frequently complete those attempts), they do not generally ask their physician for assistance in the suicide. Persons with factitious disorder (choice C) are seeking primary gain, often for dependency needs, and are seeking to enter the "sick role" not the "dead role."

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9.

A 26-year-old man presents to his physician with a chronic cough. The man is a smoker, and states that he also gets frequent headaches and aches in his legs when he exercises. Chest x-ray demonstrates notching of his ribs. Which of the following undiagnosed congenital defects may be responsible for these findings?

Coarctation of the aorta
Eisenmenger's syndrome
Tetralogy of Fallot
Transposition of great vessels
Ventricular septal defect

Correct Answer

A. Coarctation of the aorta

Explanation

Coarctation of the aorta occurs in two patterns. In the infantile type, the stenosis is proximal to the insertion of the ductus arteriosus (preductal); this pattern is associated with Turner's syndrome. In the adult form, the stenosis is distal to the ductus arteriosus (postductal) and is associated with notching of the ribs (secondary to continued pressure from the aorta on them), hypertension in the upper extremities, and weak pulses in the lower extremities. Headache, cold extremities, and lower extremity claudication with exercise are typical if the patient is symptomatic (many adults with mild distal coarctation may remain asymptomatic for years). Upper extremity hypertension with weak pulses in the lower extremities, and a midsystolic (or continuous) murmur over the chest or back may be the only obvious signs in some. Note that the chronic cough is probably related to the man's smoking, and is not caused by the coarctation. Eisenmenger's syndrome (choice B) is a shift from a left-to-right shunt to a right-to-left shunt secondary to pulmonary hypertension. Tetralogy of Fallot (choice C) and transposition of great arteries (choice D) cause cyanosis and are usually diagnosed in infancy. Ventricular septal defect (choice E) might remain undiagnosed until adulthood, but would not cause notching of the ribs.

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10.

A 30-year-old pregnant woman complains to her physician of feeling very tired during her pregnancy. A complete blood count with differential reveals a hematocrit of 30%, with hypersegmented neutrophils and large, hypochromic red cells. Deficiency of which of the following would be most likely to produce these findings?

Ascorbic acid
Calcium
Copper
Folate
Iron

Correct Answer

A. Folate

Explanation

The patient has a megaloblastic anemia, which can be due to deficiency of folate or B12. Pregnancy increases the need for folate and other nutrients used by both baby and mother, and may "unmask" a borderline dietary deficiency. For this reason, most obstetricians recommend vitamin supplements for pregnant women. Ascorbic acid (choice A) is vitamin C, and its deficiency predisposes for capillary fragility and oral lesions. Calcium deficiency (choice B) predisposes for osteoporosis/osteopenia. Copper deficiency (choice C) is rare; when it occurs, it may cause a hypochromic anemia, neutropenia, osteoporosis, or hypotonia. Iron deficiency (choice E) causes a microcytic, hypochromic anemia, with reduced mental and physical performance.

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11.

A 54-year-old alcoholic presents with complaints of tremors and muscle twitching. Physical examination reveals the presence of Trousseau's sign. Laboratory data show that serum magnesium is < 1 mEq/L (normal, 1.4 - 2.2 mEq/L). Which of the following findings would be most consistent with this information?

Decreased serum calcium
Decreased serum phosphate
Increased bone density
Increased plasma parathyroid hormone concentration
Increased urinary cAMP concentration

Correct Answer

A. Decreased serum calcium

Explanation

Malnutrition associated with chronic alcoholism can lead to a severe magnesium deficiency. The effect of low serum magnesium on parathyroid hormone secretion (PTH) depends on severity and duration. An acute decrease in serum magnesium will increase PTH secretion, while a prolonged severe deficiency results in
decreased PTH secretion. There is also evidence that the action of PTH is decreased with chronic magnesium deficiency. Hence, this patient is suffering from "functional" hypoparathyroidism. The low serum calcium can produce weakness, tremors, muscle fasciculations, and seizures. A positive Trousseau's sign indicates the presence of latent tetany. It is observed by inflating a blood pressure cuff above systolic blood pressure for at least 2 minutes. A positive reaction consists of the development of carpal spasm, with relaxation occurring within seconds after deflating the cuff. In patients with magnesium deficiency, magnesium administration will produce a prompt rise in plasma PTH with subsequent restoration of serum calcium concentration to normal. With functional hypoparathyroidism bone density would be decreased (not increased, choice C). The combination of decreased PTH secretion (not increased, choice D) and decreased effectiveness of PTH produce hypocalcemia and hyperphosphatemia (not hypophosphatemia, choice B). Urinary cAMP would probably be decreased (not increased, choice E), given the low PTH.

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12.

A 35-year-old woman notices a change in the appearance of a mole on her neck. Physical examination reveals that the lesion is an irregular, nodular, superficial mass with a variegated appearance. Biopsy demonstrates a primary malignant tumor. Which of the following factors is most predictive of the patient's long term prognosis?

Circumference of lesion
Darkness of lesion
Degree of color variation
Depth of lesion
Sharpness of border between lesion and adjacent skin

Correct Answer

A. Depth of lesion

Explanation

The lesion is a malignant melanoma. Melanomas can develop either de novo or in an existing mole. Sunlight exposure is a significant risk factor and fair-skinned persons are at increased risk of developing melanoma. The most significant factor for long term prognosis is the depth of the lesion, since the superficial dermis lies about 1 mm under the skin surface, and penetration to this depth is associated with a much higher incidence of metastasis than is seen with a more superficial location. The circumference of the lesion (choice A) is much less important than depth, since one form of melanoma (superficial spreading) can still have good prognosis despite large size, if it has not extended to the depth of the superficial dermal lymphatic bed. The darkness (choice B) or degree of variation in color (choice C) do not have prognostic significance once melanoma is diagnosed. Irregularity, or fuzziness at the border (choice E) of a mole-like lesion is a good clue to potential malignancy, but does not affect prognosis once a melanoma is diagnosed.

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13.

A 48-year-old female is being treated for breast carcinoma. Over the past few days, she has been complaining of dysuria and frequency. Laboratory examination revealed the presence of microscopic hematuria. The next day the patient developed gross hematuria. Which of the following agents most likely caused the development of these signs and symptoms?

Cyclophosphamide
Mitomycin
Paclitaxel
Tamoxifen
Vincristine

Correct Answer

A. Cyclophosphamide

Explanation

Cyclophosphamide is metabolized to acrolein, which is excreted in the urine. If the patient's urine is concentrated, the toxic metabolite may cause severe bladder damage. Early symptoms of bladder toxicity include dysuria and frequency. This can be distinguished from a urinary tract infection, since there is no bacteriuria with cyclophosphamide-induced bladder toxicity. However, microscopic hematuria is often present on urinalysis. In severe hemorrhagic cystitis, large segments of the bladder mucosa may be shed which can lead to prolonged, gross hematuria. The incidence of cyclophosphamide-induced hemorrhagic cystitis can be decreased by ensuring that the patient maintains a high fluid intake. Cyclophosphamide is an alkylating agent used in the treatment of breast carcinoma, malignant lymphoma, multiple myeloma, and adenocarcinoma of the ovary, as well as various other forms of cancer. The major toxic reactions commonly seen with this agent include mucositis, nausea, hepatotoxicity, sterile hemorrhagic and non-hemorrhagic cystitis, leukopenia, neutropenia, and interstitial pulmonary fibrosis. Mitomycin (choice B) is an antibiotic antineoplastic agent used in the treatment of breast carcinoma, adenocarcinoma of the pancreas and stomach, as well as various other forms of cancer. The major toxic reactions commonly seen with this agent include bone marrow depression, nausea, hepatotoxicity, acute bronchospasm, thrombocytopenia, and interstitial pneumonitis. Paclitaxel (choice C) is an antineoplastic agent primarily used in the treatment of ovarian and breast cancer. The major toxic reactions commonly seen with this agent include bone marrow depression, nausea, hepatotoxicity, bronchospasm, thrombocytopenia, and neutropenia. Tamoxifen (choice D) is an antineoplastic hormone primarily used in the palliative treatment of estrogen-receptor positive breast cancer patients. The major toxic reactions commonly seen with this agent include depression, dizziness, thrombosis, mild leukopenia or thrombocytopenia. Vincristine (choice E) is a mitotic inhibitor antineoplastic agent used in the treatment of breast cancer, Hodgkin'sdisease, non-Hodgkin's lymphoma, advanced testicular cancer and various other types of cancer. The major toxic reactions commonly seen with this agent include mental depression, hemorrhagic enterocolitis, bone marrow depression, nausea, thrombocytopenia, and leukopenia

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14.

A patient develops fever, shortness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?

AIDS
Congestive heart failure
Pulmonary embolus
Rheumatoid arthritis
Systemic lupus erythematosus

Correct Answer

A. AIDS

Explanation

The disease is Pneumocystis pneumonia, which is caused by an agent now believed to be a fungus rather than a true bacteria. Pneumocystis carinii pneumonia is seen in immunocompromised patients, particularly in those with AIDS, cancer, and in malnourished children. It can be the AIDS-defining illness. Congestive heart failure (choice B) predisposes the patient to pulmonary edema. Pulmonary embolus (choice C) can cause pulmonary infarction or sudden death. Rheumatoid arthritis (choice D), particularly in miners, can cause formation of lung nodules similar to subcutaneous rheumatoid nodules. Systemic lupus erythematosus (choice E) can cause pleuritis, but is not associated with a significantly increased incidence of pneumonia.

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15.

The blood from an 8-year-old boy was analyzed by flow cytometry . The exact number of B cells was counted. Which of the following cell surface markers was likely used to identify the B cells in this blood sample?

CD3
CD4
CD8
CD19
CD56

Correct Answer

A. CD19

Explanation

The best markers for identification of B cells are CD19, CD20, and CD21. The CD21 marker is a receptor for EBV (Epstein-Barr Virus). The CD3 marker (choice A) is present on all T cells with either a CD4 or CD8 marker. This is the marker that is used to identify total T cell count in a blood sample. The CD3 marker is used for signal transduction in the different T cells. The CD4 marker (choice B) is used to identify T helper cells. These are the cells that recognize exogenous peptides presented on MHC class II molecules by macrophages. CD4+ T helper cells are also involved in cell-mediated delayed hypersensitivity, production of cytokines for stimulation of antibody production by B cells, and stimulation of macrophages. The CD8 marker (choice C) is used to identify cytotoxic T cells. These are the cells that recognize viral epitopes attached to the MHC class I molecules of a virally infected cell. The CD56 marker (choice E) is used to identify NK(natural killer) cells. These cells are important in innate host defense, specializing in killing virally infected cells and tumor cells by secreting granzymes and perforins

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16.

The wife of a 48-year-old male patient brings him to the emergency room and says that his memory has progressively gotten worse over the last several years. She also says his personality has been changing. The physician notes abnormal writhing movements of the man's limbs and hyperreactive reflexes. MRI reveals a loss of volume in the neostriatum and cortex. This disease is inherited via an

Autosomal dominant trait
Autosomal recessive trait
X-linked dominant trait
X-linked recessive trait

Correct Answer

A. Autosomal dominant trait

Explanation

This patient has Huntington's disease, which has autosomal dominant inheritance. It is characterized by severe degeneration of the caudate nucleus along with degenerative changes in the putamen and cortex. In addition to chorea, these patients frequently suffer from athetoid (writhing) movements, progressive dementia, and behavioral disorders.

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17.

A 33-year-old single mother of two young children visits her physician because of an oral ulcer. A review of systems is significant for fatigue, myalgia, and joint pain. Laboratory results demonstrate leukopenia, and a high-titered antinuclear antibody. A speckled staining pattern due to anti-Sm is seen with immunofluorescence; urinary protein is elevated. Which of the following is the most likely diagnosis?

Generalized fatigue
Goodpasture's syndrome
Mixed connective tissue disease
Scleroderma
Systemic lupus erythematosus

Correct Answer

A. Systemic lupus erythematosus

Explanation

Systemic lupus erythematosus (SLE) is a prototype connective tissue disease. The diagnosis requires four criteria to be met from a list of eleven possible criteria: malar rash, discoid rash, photosensitivity, oral ulcers, arthritis, serositis, renal disorder, neurologic disorder, hematologic disorder, immunologic disorder, and antinuclear antibody. This patient also has anti-Sm, which is pathognomonic for SLE, but is only found in 30% of the affected patients. Antinuclear antibodies (ANA) are present in 95-100% of cases of SLE; anti-double-stranded DNA is found in 70% of the cases. Generalized fatigue (choice A) due to being a single working mother of two children could well be a possibility, but the presence of the other criteria make SLE more likely. Goodpasture's syndrome (choice B) is characterized by linear disposition of immunoglobulin, and often C3, along the glomerular basement membrane (GBM). Glomerulonephritis, pulmonary hemorrhage, and occasionally idiopathic pulmonary hemosiderosis occur. Mixed connective tissue disease (choice C) is an overlap syndrome characterized by a combination of clinical features similar to those of SLE, scleroderma, polymyositis, and rheumatoid arthritis. These patients generally have a positive ANA in virtually 100% of the cases. High titer anti-ribonucleoprotein (RNP) antibodies may be present, generating a speckled ANA pattern. Anti-RNP is not pathognomonic for mixed connective tissue disease, since it can be found in low titers in 30% of the patients with SLE. Scleroderma (choice D) is characterized by thickening of the skin caused by swelling and thickening of fibrous tissue, with eventual atrophy of the epidermis. ANA are often associated with the disease, but the staining pattern is generally nucleolar.

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18.

A 43-year-old man is brought to the general medicine clinic by his wife. She states that his memory has progressively deteriorated over the last several years, and that his personality has been changing. On examination, the physician notes abnormal, writhing movements of the man's limbs and hyperreactive patellar reflexes. An MRI of the head reveals a loss of volume in the neostriatum and cortex. A family history reveals that similar symptoms occurred in several members of the patient's family. Which of the following genetic mechanisms has been implicated in this disorder?

Expanded trinucleotide tandem repeat
Genomic imprinting
Large deletion in one gene
Single amino acid substitution
Translocation

Correct Answer

A. Expanded trinucleotide tandem repeat

Explanation

The disease described is Huntington's disease, which is now known to be related to an expanded trinucleotide tandem repeat on the short arm of chromosome 4. The number of trinucleotide repeats frequently increases in succeeding generations during the process of spermatogenesis. Prader-Willi and Angelman syndromes are frequently cited examples of genetic diseases involving genomic imprinting (choice B). Duchenne's muscular dystrophy is an example of a disease that is frequently due to a large deletion in a single gene (choice C). Single amino acid substitutions (choice D) are common in recessive diseases such as sickle cell anemia. Translocations (choice E) occur in disorders such as chronic myelogenous leukemia (CML; Philadelphia chromosome) and some cases of Down's syndrome.

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19.

A 28-year-old female presents to the doctor complaining of syncopal episodes that last a few minutes. She is not taking any medications and has no previous medical history. EEG and EKG studies are performed and are unremarkable. An echocardiogram shows a single ball-shaped mass dangling in the left atrium near the mitral valve. The most likely diagnosis is

Angiosarcoma
Mesothelioma
Myxoma
Rhabdomyoma
Rhabdomyosarcoma

Correct Answer

A. Myxoma

Explanation

The vignette illustrates a typical presentation for a tumor of the heart. Primary cardiac tumors are rare and usually require an intensive work-up to pinpoint the diagnosis. 75% of primary cardiac tumors are benign and among these, myxoma is the most common. The tumors are usually single; the most common location is the left atrium. They may cause syncopal episodes or even shock and death due to obstruction by a "ball valve" mechanism. Angiosarcoma (choice A) is a malignant tumor of vascular origin that can occur as a primary cardiac tumor. It is the most common malignant primary cardiac tumor, but it is still very rare. Angiosarcoma usually affects the right side of the heart. Mesothelioma (choice B) is a benign tumor of mesothelial origin that can rarely present as a primary cardiac tumor. It is usually a small intramyocardial tumor that presents with disturbances of the conduction system of the heart. Rhabdomyoma (choice D) is a benign tumor of muscle origin. It can occur as a primary cardiac tumor, typically in infants and children, in whom it may be associated with tuberous sclerosis. It usually occurs in the ventricles. Rhabdomyosarcoma (choice E) is a malignant neoplasm that can also occur as a rare primary cardiac tumor. It is of muscle origin and usually affects the right heart.

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20.

A 27-year-old white male presents with a 3-week history of several swollen and painful toes and knees. He has a past history of conjunctivitis. He also describes some low back stiffness that is more severe in the morning. Which of the following is the most likely diagnosis?

Gout
Lyme disease
Reiter's syndrome
Rheumatoid arthritis
Septic arthritis

Correct Answer

A. Reiter's syndrome

Explanation

This is a case of Reiter's syndrome. Patients typically present with the acute onset of arthritis (usually asymmetric and additive), with involvement of new joints occurring over a period of a few days to 2 weeks. Joints of the lower extremities are the most commonly involved, but wrists and fingers can also be affected. Dactylitis (sausage digit), a diffuse swelling of a solitary finger or toe, is a distinctive feature of Reiter's arthritis and psoriatic arthritis. Tendonitis and fasciitis are common. Spinal pain and low back pain are common. Conjunctivitis, urethritis, diarrhea, and skin lesions are also associated with Reiter's syndrome. Up to 75% of patients are HLA-B27 positive. Microorganisms which can trigger Reiter's syndrome include Shigella spp., Salmonella spp., Yersinia spp., Campylobacter jejuni, and Chlamydia trachomatis. Most patients are younger males. Gout (choice A) usually presents as an explosive attack of acute, very painful, monarticular inflammatory arthritis. Hyperuricemia is the cardinal feature and prerequisite for gout. The first metatarsophalangeal joint is involved in over 50% of first attacks. Lyme disease (choice B), caused by Borrelia burgdorferi, presents with a red macule or papule at the site of the tick bite. This lesion, called erythema chronicum migrans, slowly expands to form a large annular lesion with a red border and central clearing. The lesion is warm, but usually not painful. The patient also has severe headache, stiff neck, chills, arthralgias, and profound malaise and fatigue. Untreated infection is associated with development of arthritis. The large joints (e.g., knees) are usually involved with the arthritis lasting for weeks to months. Rheumatoid arthritis (choice D) begins insidiously with fatigue, anorexia, generalized weakness, and vague musculoskeletal symptoms leading up to the appearance of synovitis. Pain in the affected joints, aggravated by movement, is the most common manifestation of established rheumatoid arthritis. Generalized stiffness is frequent and is usually greatest after periods of inactivity. Morning stiffness of greater than 1 hour in duration is very characteristic. Rheumatoid arthritis is more common in females. The metacarpophalangeal and proximal interphalangeal joints of the hands are characteristically involved. Septic arthritis (choice E) is caused by a variety of microorganisms, including Neisseria gonorrhoeae and Staphylococcus aureus. Hematogenous spread is the most common route in all age groups. 90% of patients present with involvement of a single joint, usually the knee. The usual presentation is moderate-to-severe pain, effusion, muscle spasm, and decreased range of motion. Peripheral leukocytosis and a left shift are common. Disseminated gonococcal infections present as fever, chills, rash, and articular symptoms. Papules progressing to hemorrhagic pustules develop on the trunk and extensor surfaces of the distal extremities. Migratory arthritis and tenosynovitis of multiple joints is common.

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21.

An otherwise healthy 3-year-old child is brought to the pediatrician with umbilicated, flesh-colored papules on his trunk. This condition is related to infection with which of the following viruses?

Cytomegalovirus
Herpesvirus 6
Parvovirus
Poxvirus
Variola

Correct Answer

A. Poxvirus

Explanation

The lesions are characteristic of molluscum contagiosum, which is a typically benign and self-limited condition caused by a poxvirus. The disease can be transmitted either venereally or through non-venereal contact. The other viruses listed do not cause similar skin lesions. Patients with advanced HIV infection may develop a severe, generalized, and persistent eruption, often involving the face and upper body. Cytomegalovirus (choice A) causes congenital infections and disseminated infections in immunosuppressed patients. Herpesvirus 6 (choice B)causes roseola (exanthem subitum). Parvovirus (choice C) causes aplastic crises in patients with hemolytic anemia. Variola (choice E) is the smallpox virus.

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22.

During a routine physical examination of a 74-year-old man, a physician palpates a large, pulsating mass in the lower abdomen. To which of the following is this mass most likely etiologically related?

Atherosclerosis
Bacterial infection
Congenital anomaly
Cystic medial degeneration
Syphilis

Correct Answer

A. Atherosclerosis

Explanation

The mass is an abdominal aortic aneurysm, typically found in older men. Such aneurysms are almost always related to the formation of complicated atherosclerotic plaques in the aorta. Associated coronary artery disease is commonplace. Bacterial infection (choice B) can cause "mycotic" aneurysms; these usually involve smaller vessels. The small berry aneurysms that can involve the circle of Willis are congenital anomalies (choice C). Cystic medial degeneration (choice D) is related to the development of dissecting aneurysms (actually dissecting hematomas). Tertiary syphilis (choice E) typically causes aneurysms of the root and arch of the aorta, rather than the descending aorta.

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23.

Which of the following organisms is the most common cause of community-acquired pneumonia?

Chlamydia pneumoniae
Haemophilus influenzae
Mycoplasma pneumoniae
Staphylococcus aureus
Streptococcus pneumoniae

Correct Answer

A. Streptococcus pneumoniae

Explanation

The most common bacteria implicated in community-acquired pneumonia is the pneumococcus, Streptococcus pneumoniae. Other organisms frequently implicated in patients less than age 60 without comorbidity include Mycoplasma pneumoniae, respiratory viruses, Chlamydia pneumoniae, and Haemophilus influenzae. When community-acquired pneumonia occurs in elderly patients or patients with comorbidity, aerobic gram-negative bacilli and Staphylococcus aureus are added to the list. The organisms listed in choices A, B, and C are important causes of community-acquired pneumonia, but are not the most frequent causes. Staphylococcus aureus (choice D) is an important cause of community-acquired pneumonia (particularly in the elderly and in patients with comorbidity), but is not the most frequent cause.

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24.

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

Clavicles
Femurs
Metatarsals
Phalanges
Tibias

Correct Answer

A. Clavicles

Explanation

In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull, and facial and dental anomalies. Note that you could also have answered this question by noting that of the bones listed, only the clavicles form by intramembranous ossification. The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones.

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25.

The cell in the center of the electron micrograph above is important in wound healing and plays a role in the pathological process underlying Dupuytren's contracture. Which of the following cell types is depicted?

Endothelial cell
Myoepithelial cell
Myofibroblast
Pericyte
Smooth muscle cell

Correct Answer

A. Myofibroblast

Explanation

The cell is spindle-shaped like a fibroblast; however, the difference is that the cytoplasm contains several bundles of microfilaments. These bundles are parallel to the long axis of the cell and are seen immediately beneath the cell membrane and within the cytoplasm. Densities, comparable to Z-lines, can be seen along some of these bundles. The microfilaments are responsible for the contractile properties of this cell. These contractile properties, in addition to the cell's ability to link with collagen, function in wound closure in the healing process. Dupuytren's contracture, which is a contracture of the palmar fascia, is caused by interaction of these cells with collagen fibrils of the fascia. The endothelial cell (choice A) lines vessels. There are no vessels in the photomicrograph. The myoepithelial cell (choice B) contains microfilaments and is contractile. However, it is closely associated with glandular epithelium (not apparent here). The pericyte (choice D) is a multipotential connective tissue cell found near or around blood vessels, but it does not contain microfilament bundles such as these. There are no vessels apparent in the photomicrograph. The smooth muscle cell (choice E) is joined by junctions to other smooth muscle cells, arranged in bundles. Microfilaments make up most of the cytoplasm of such cells, with the nucleus in a central location.

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26.

After falling on his laterally outstretched arm, a patient suffered a dislocation of the glenohumeral joint. Which of the following nerves is most likely to have been injured from this dislocation?

Axillary nerve
Dorsal scapular nerve
Lateral pectoral nerve
Medial pectoral nerve
Suprascapular nerve

Correct Answer

A. Axillary nerve

Explanation

When the head of the humerus dislocates from the glenohumeral joint, it exits inferiorly, where the joint capsule is the weakest. Immediately inferior to the glenohumeral joint, the axillary nerve exits from the axilla by passing through the quadrangular space. At this location, the downward movement of the head of the humerus can stretch the axillary nerve. The axillary nerve innervates the deltoid muscle after leaving the axilla. The dorsal scapular nerve (choice B) passes along the medial border of the scapula to innervate the rhomboid muscles. The nerve does not pass in the region of the glenohumeral joint. The lateral and medial pectoral nerves (choices C and D) branch from the lateral and medial cords of the brachial plexus, respectively, and exit through the anterior wall of the axilla to innervate the pectoralis major and minor. These nerves do not pass in the region of the glenohumeral joint. The suprascapular nerve (choice E) is a branch of the upper trunk of the brachial plexus and passes over the superior border of the scapula to innervate the supraspinatus and infraspinatus muscles. This nerve does not pass in the region of the glenohumeral joint.

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27.

A 70-year-old woman with a history of multiple small strokes reports to her physician that she has had multiple recent experiences that something or someone seemed very familiar, when in reality they were not familiar to her. This type of experience is called which of the following?

Anterograde amnesia
Confabulation
Deja vu
Jamais vu
Retrograde amnesia

Correct Answer

A. Deja vu

Explanation

This is deja vu ("seen before"), which is the experience of an event, person, or thing as familiar, even though it has never previously been experienced. Severe cases often accompany an underlying neurologic problem. Anterograde amnesia (choice A) is the inability to learn new facts. Most commonly, it involves both verbal and nonverbal material, but it can involve one or the other. In confabulation (choice B), a patient reports "memories" of events that did not take place at the time in question. In jamais vu (choice D), a patient fails to recognize familiar events that have been encountered before. In retrograde amnesia (choice E), a patient fails to remember facts or events that occurred before the onset of amnesia.

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28.

A woman presents to a dermatologist because she has lost almost all the hair on her body, including scalp hair, eyebrows, eyelashes, armpit, and groin hair, and the fine hairs on her body and extremities. Does she most likely have a variant of which of the following?

Alopecia areata
Androgenic alopecia
Chronic cutaneous lupus erythematosus
Lichen planopilaris
Trichotillomania

Correct Answer

A. Alopecia areata

Explanation

Alopecia areata is caused by an autoimmune attack on hair follicles. It has a wide range of clinical severity, with most cases involving a localized patch of hair (which regrows within 1 year in half of the patients). The hair that does regrow may be gray or depigmented. More severe cases can involve the entire scalp (alopecia totalis) or, as in this patient, the entire body surface (alopecia universalis). These more severe cases are less likely to resolve adequately. Treatment of alopecia areata is often unsuccessful, but topical steroids are typically tried. Androgenic alopecia (choice B) is common male pattern baldness. Chronic cutaneous lupus erythematosus (choice C) can produce localized baldness. Lichen planopilaris (choice D) can produce localized baldness. Trichotillomania (choice E), also called traumatic alopecia, is alopecia due to trauma, such as hair pulling or tight braids.

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1

29.

During embryological development, hematopoiesis occurs in different organs at different times. Which of the following are the correct organs, in the correct sequence, at which hematopoiesis occurs embryologically?

Amnion, yolk sac, placenta, bone marrow
Placenta, liver and spleen, yolk sac, bone marrow
Placenta, spleen and lymphatic organs, bone marrow
Yolk sac, bone marrow, liver and spleen
Yolk sac, liver, spleen and lymphatic organs, bone marrow

Correct Answer

A. Yolk sac, liver, spleen and lymphatic organs, bone marrow

Explanation

By the third week of development, hematopoiesis begins in the blood islands of the yolk sac. Beginning at 1 month of age and continuing until 7 months of age, blood elements are also formed in the liver. Hematopoiesis occurs in the spleen and lymphatic organs between 2 and 4 months, and in the bone marrow after 4 months.

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30.

A 42-year-old female presents with a recent onset of fatigue, malaise, constipation, and a 12-pound weight gain. On examination, her thyroid is firm and enlarged. What laboratory test is most likely to confirm the expected diagnosis?

Antithyroid antibodies
Serum thyroid-stimulating hormone (TSH) measurement
Serum thyroxine (T4) measurement
Serum triiodothyronine (T3) measurement
T3 resin uptake

Correct Answer

A. Serum thyroid-stimulating hormone (TSH) measurement

Explanation

The patient's presentation is consistent with hypothyroidism. Serum thyroid-stimulating hormone (TSH) measurement (choice B) is most likely to confirm the empiric diagnosis. TSH levels usually rise above normal before serum thyroxine (T4; choice C) and serum triiodothyronine (T3; choice D) levels do, even in mild cases of hypothyroidism. Therefore, TSH measurement would be the most accurate test to determine the presence of hypothyroidism regardless of the severity. A high titer of antithyroid antibodies (choice A) is characteristic of chronic thyroiditis, which is the most common cause of hypothyroidism. However, detection of these antibodies would not indicate if hypothyroidism was present.T3 resin uptake (choice E) measurement is not an accurate test of thyroid function; it is primarily used to exclude various abnormalities in the thyroid-hormone binding proteins

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31.

5 mL of synovial fluid is aspirated from an inflamed knee joint. The fluid is yellow-white and cloudy and contains 200,000 WBC/mm3 (85% neutrophils). Needle-shaped, strongly negatively birefringent crystals are seen both within and outside neutrophils. These crystals most likely have which of the following compositions?

Basic calcium phosphate
Calcium oxalate
Calcium pyrophosphate dihydrate
Cholesterol
Monosodium urate

Correct Answer

A. Monosodium urate

Explanation

All the compounds listed can produce crystals in joint fluid, but only monosodium urate (associated with gout) and calcium pyrophosphate dihydrate (associated with CPPD crystal deposition disease, also called pseudogout), and to lesser degree basic calcium phosphate (apatite-associated arthropathy), have a high likelihood of being encountered on a step 1 USMLE exam. The crystals described are those of monosodium urate. Be careful not to answer "uric acid" if that is listed as an alternative choice on an exam, since the sodium salt is the predominant species in vivo. Basic calcium phosphate (choice A) is seen in apatite-associated arthropathy and produces spherical clumps of nonbirefringent submicroscopic crystals. Calcium oxalate crystals (choice B) are seen in primary oxalosis and are bipyramidal, positively birefringent crystals. Calcium pyrophosphate dihydrate crystals (choice C) are a feature of pseudogout and are rod-to-rhomboidal-shaped, weakly positively birefringent crystals. Cholesterol crystals (choice D) are seen in chronic and chylous effusions in inflammatory and degenerative arthritis, where they form large, flat, rhomboidal plates with notched corners. --------------------------------------------------------------------------------

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32.

Which of the following renal structures is most medially located?

Major calyx
Minor calyx
Renal cortex
Renal pelvis
Renal pyramid

Correct Answer

A. Renal pelvis

Explanation

This is a relatively simple question that requires you to visualize the relationship among the key parts of the kidney and to identify the one that lies most medially. If you think about it for a second, since the kidneys ultimately drain into the ureter at their medial poles, you are looking for the structure that is closest to the ureter. The correct answer is the renal pelvis. The renal pelvis is the dilated upper portion of the ureter that receives the major calyces. In terms of the other answer choices, the order from most lateral to most medial is: renal cortex (choice C), renal pyramid (choice E), minor calyx (choice B), major calyx (choice A), and then the renal pelvis (choice D).

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33.

A Guatemalan child with a history of meconium ileus is brought to a clinic because of a chronic cough. The mother notes a history of respiratory tract infections and bulky, foul-smelling stools. After assessment of the respiratory tract illness, the physician should also look for signs of

Cystinuria
Hypoglycemia
Iron deficiency anemia
Sphingomyelin accumulation
Vitamin A deficiency

Correct Answer

A. Vitamin A deficiency

Explanation

The child is likely suffering from cystic fibrosis. In this disorder, an abnormality of chloride channels causes all exocrine secretions to be much thicker, and more viscous than normal. Pancreatic secretion of digestive enzymes is often severely impaired, with consequent steatorrhea and deficiency of fat-soluble vitamins, including vitamin A. Cystinuria (choice A) is a relatively common disorder in which a defective transporter for dibasic amino acids (cystine, ornithine, lysine, arginine; COLA) leads to saturation of the urine with cystine, which is not very soluble in urine, and precipitates out to form stones. Hypoglycemia (choice B) is not a prominent feature of children with cystic fibrosis who are on a normal diet. Hyperglycemia may occur late in the course of the disease. Iron deficiency anemia (choice C) is not found with any regularity in children with cystic fibrosis. Sphingomyelin accumulation (choice D) is generally associated with deficiency of sphingomyelinase, as seen in Niemann-Pick disease.

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34.

A liver biopsy from a 54-year-old man shows many Mallory bodies. This finding is most suggestive of which of the following diseases?

Alcohol abuse
Alpha1-antitrypsin deficiency
Hepatitis A
Hepatitis B
Wilson's disease

Correct Answer

A. Alcohol abuse

Explanation

Mallory bodies are eosinophilic cytoplasmic inclusions ("alcoholic hyaline") that are found in the largest numbers in alcoholic hepatitis. They were originally considered to be pathognomic of alcohol abuse, but have since been found (in much smaller numbers) in many other liver conditions. Alpha1-antitrypsin deficiency (choice B) involvement of the liver is characterized by periodic acid Schiff (PAS)-positive cytoplasmic granules in hepatocytes. Hepatitis A (choice C) and hepatitis B (choice D) infections are definitively established with serologic markers. In Wilson's disease (choice E), there is excess copper deposition in the liver

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35.

A 38-year-old pregnant woman with a past medical history significant for chronic hypertension presents with a blood pressure of 158/105 mm Hg. Which of the following antihypertensive agents would be most suitable for initial therapy in this patient?

Bumetanide
Fosinopril
Hydrochlorothiazide
Methyldopa
Valsartan

Correct Answer

A. Methyldopa

Explanation

Pregnant women with chronic hypertension "require" antihypertensive therapy when the diastolic pressure is greater than 100 mm Hg; however, some clinicians may decide to treat patients with diastolic blood pressures less than 100 mm Hg. For the initiation of therapy, methyldopa is still considered to be the agent of choice. Methyldopa is converted intraneuronally to a-methylnorepinephrine, an alpha-2 adrenergic agonist, which is subsequently released. Release of a-methylnorepinephrine in the medulla leads to a decrease in sympathetic outflow, thus lowering blood pressure. Methyldopa has been safely used in the treatment of hypertension during pregnancy; this agent is not associated with the development of teratogenic or other fetal abnormalities. Diuretics, such as bumetanide (choice A) and hydrochlorothiazide (choice C), are often avoided since these agents can produce hypovolemia, leading to reduced uterine blood flow. Although these agents can be used during pregnancy, methyldopa and hydralazine are the drugs of choice for hypertension during pregnancy. Fosinopril (choice B) is an angiotensin-converting enzyme (ACE) inhibitor that should not be administered to pregnant women, especially in the second or third trimesters. These agents have been associated with severe fetal and neonatal injury, such as hypotension, neonatal skull hypoplasia, anuria, renal failure, and death. Along the same lines, the use of the angiotensin II receptor antagonists, such as valsartan (choice E), is not recommended since these agents cause fetal complications similar to the ACE inhibitors

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36.

A surgical pathology specimen from a 24-year-old woman seen at a reproductive medicine clinic demonstrates a ciliated columnar epithelium. From which of the following locations in the female genital tract was the biopsy obtained?

Cervix
Endometrium
Fallopian tube
Ovary
Vagina

Correct Answer

A. Fallopian tube

Explanation

The fallopian tube is the only structure in the female genital tract with a ciliated columnar epithelium; the beating of the cilia helps move the egg into the uterus. This fact is also sometimes clinically helpful since dilated and deformed fallopian tubes can be microscopically distinguished from cystic ovarian tumors by the presence of the cilia. The cervix (choice A) and vagina (choice E) are lined by squamous epithelium. The endometrium (choice B) is lined by columnar epithelium (although a few ciliated cells may be present). The covering of the ovary (choice D) is cuboidal epithelium, and cysts within the ovary can be lined by cuboidal or non-ciliated columnar epithelium.

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37.

A 54-year-old male with acute lymphocytic leukemia develops a blast crisis. He is treated with intensive systemic chemotherapy. Following treatment, the patient will be at increased risk for the development of

Bile pigment gallstones
Cholesterol gallstones
Cystine kidney stones
Struvite kidney stones
Uric acid kidney stones

Correct Answer

A. Uric acid kidney stones

Explanation

Uric acid kidney stones in patients with leukemia are secondary to increased production of uric acid from purine breakdown during periods of active cell proliferation, especially following treatment. Vigorous hydration and diuresis are generally instituted after the diagnosis of acute leukemia is made. Uric acid kidney stones are also associated with inborn errors of purine metabolism, such as gout. Pigment gallstones (choice A) are associated with hemolytic disease. The incidence of this type of gallstone is not increased in treated leukemias. Cholesterol gallstones (choice B) are associated with diabetes mellitus, obesity, pregnancy, birth control pills, and celiac disease. Cystine kidney stones (choice C) are rare; they are found in cystinuria. Struvite kidney stones (choice D) are associated with infection by urea-splitting organisms, such as Proteus

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38.

A 65-year-old man with mild heart failure is treated with a loop diuretic . A few days later the man complains of muscle weakness. Laboratory results are shown below. Arterial PCO2: 48 mm Hg Arterial pH: 7.49 Plasma HCO3-: 35 mEq/L Which of the following is most likely decreased in this man?

Plasma aldosterone
Plasma potassium
Potassium excretion
Renin secretion
Sodium excretion

Correct Answer

A. Plasma potassium

Explanation

The data shown in the table indicate that the man has developed metabolic alkalosis (increased PCO2, pH, and HCO3-), which occurs commonly with overuse of diuretics (thiazides and loop diuretics). The overuse of a loop diuretic increases the excretion of sodium (choice E) and potassium (choice C) by the kidneys. The increase in potassium excretion leads to a decrease in plasma potassium levels (choice B). The decrease in plasma potassium stimulates aldosterone secretion, which raises plasma aldosterone levels (choice A). The sodium depletion stimulates renin secretion (choice D), which in turn raises angiotensin II levels in the plasma (which also stimulates aldosterone secretion

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39.

Which of the following hormones is secreted by anterior pituitary cells that stain with acidic dyes?

ACTH
FSH
LH
Prolactin
TSH

Correct Answer

A. Prolactin

Explanation

The cells of the anterior pituitary can be classified as chromophils (love dyes) or chromophobes (do not stain with dyes). The chromophils can be further divided into acidophils (stain with acidic dyes) and basophils (stain with basic dyes). The acidophils include the somatotropes, which secrete growth hormone, and the mammotropes, which secrete prolactin. The basophils include the corticotropes, which secrete ACTH (choice A), the gonadotropes, which secrete FSH and LH (choices B and C), and the thyrotropes, which secrete TSH (choice E).

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40.

A 45-year-old homeless man has a chronic cough, a cavitary lesion of the lung, and is sputum positive for acid-fast bacilli. Which of the following is the principle form of defense by which the patient's body fights this infection?

Antibody-mediated phagocytosis
Cell-mediated immunity
IgA-mediated hypersensitivity
IgE-mediated hypersensitivity
Neutrophil ingestion of bacteria

Correct Answer

A. Cell-mediated immunity

Explanation

The principle host defense in mycobacterial infections (such as this patient's tuberculosis) is cell-mediated immunity, which causes formation of granulomas. Unfortunately, in tuberculosis and in many other infectious diseases characterized by granuloma formation, the organisms may persist intracellularly for years in the
granulomas, only to be a source of activation of the infection up to decades later. While antibody-mediated phagocytosis (choice A) is a major host defense against many bacteria, it is not the principle defense against Mycobacteria. IgA-mediated hypersensitivity (choice C) is not involved in the body's defense against Mycobacteria. IgE-mediated hypersensitivity (choice D) is not involved in the body's defense against Mycobacteria. It is important in allergic reactions. Neutrophil ingestion of bacteria (choice E) is a major host defense against bacteria, but is not the principle defense against Mycobacteria.

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41.

Which of the following would shift the oxygen-hemoglobin dissociation curve to the right?

Carbon monoxide poisoning
Decreased PCO2
Decreased pH
Decreased temperature
Decreased 2,3-DPG

Correct Answer

A. Decreased pH

Explanation

The loading of O2 is facilitated when the oxygen dissociation curve shifts to the left, and the unloading of O2 is facilitated when the oxygen dissociation curve shifts to the right. A good way to remember the conditions that promote dissociation of O2 is to think of exercising muscle, which has decreased pH (choice C) because of the accumulation of lactic acid, increased PCO2 (compare with choice B) because of the increased rate of aerobic metabolism, increased temperature (compare with choice D), and increased 2,3-DPG (2,3-diphosphoglycerate; compare with choice E) because of increased glycolysis. Carbon monoxide poisoning (choice A) left-shifts the oxygen dissociation curve, which interferes with the unloading of O2. Carbon monoxide also strongly binds to available sites on hemoglobin.

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42.

A 27-year-old woman is giving birth. During the birth, the placental membranes tear and amniotic fluid is expressed into a lacerated cervical vein. Which of the following is the woman most likely to experience immediately following this event?

Hemiplegia
Placental abruption
Renal failure
Respiratory distress
Splinter hemorrhages

Correct Answer

A. Respiratory distress

Explanation

Respiratory distress immediately follows amniotic fluid embolism as the emboli consisting of squamous cells, lanugo, and mucus deposit in the pulmonary microcirculation, producing numerous tiny pulmonary infarcts. The dramatic respiratory distress may also reflect the action of prostaglandins and other bioactive compounds present in high concentrations in the amniotic fluid embolus. Hemiplegia (choice A) would reflect an ischemic injury to one hemisphere of the cerebrum or the brainstem. A venous embolus would not produce such an insult. Placental abruption (choice B) is partial, premature separation of the placental disc from the endometrium. Although abruption may occur in this setting, it is not a result of an amniotic fluid embolism. There are numerous causes of renal failure (choice C); the most likely ones in the peripartum interval include eclampsia, hypovolemic shock, and ascending infections. Amniotic fluid embolism would be expected to produce severe dyspnea well before shock and renal failure might arise. Splinter hemorrhages (choice E) are small hemorrhages seen on toes and fingers due to a shower of microemboli arising in the arterial circulation. Amniotic fluid emboli arise in the veins and deposit in the lungs.

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43.

A 15-year-old boy is evaluated by a clinician for failure to develop norma l male secondary sexual characteristics. Physical examination reveals small testes, a small penis, and gynecomastia. The boy has had some difficulties in school, and the parents say that the school psychometrist said he had an IQ of 90. This patient's condition is most likely to be related to which of the following?

Deletion
Nondisjunction of an autosomal chromosome
Nondisjunction of a sex chromosome
Non-Robertsonian translocation
Robertsonian translocation

Correct Answer

A. Nondisjunction of a sex chromosome

Explanation

The boy probably has Klinefelter's syndrome (47, XXY), which has the typical presentation described in the question. The condition arises as a result of failure of separation (nondisjunction) of the sex chromosomes, and can be related to either paternal nondisjunction (slightly more common) or maternal nondisjunction. Deletions (choice A) are a common form of genetic disease and contribute to many genetic recessive diseases. Examples of nondisjunction of autosomes (choice B) include trisomies such as most cases of Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18), and Patau syndrome (trisomy 13). There are two types of translocations: non-Robertsonian (choice D) and Robertsonian (choice E). Non-Robertsonian (reciprocal) translocations result when two non-homologous chromosomes exchange genetic material. Robertsonian translocations are a special type of translocation that involve exchange of genetic material from the long arms of one acrocentric chromosome to the long arms of another acrocentric chromosome, with fusion of the centromeres. Four percent of cases of Down's syndrome are caused by this mechanism.

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44.

A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?

Legionella pneumophila
Listeria monocytogenes
Spirillium minus
Staphylococcus aureus
Streptococcus pneumoniae

Correct Answer

A. Legionella pneumophila

Explanation

The patient has a severe, potentially fatal, pneumonia with prominent systemic symptoms. Culture on BCYE is the specific clue that the organism is Legionella pneumophila. The disease is respiratory Legionellosis, also known as Legionnaire's disease, because the disease was first described when it occurred in epidemic form following an American Legion convention at a Philadelphia hotel. Patients tend to be older (40-70 years old) and may have risk factors including cigarette use, alcoholism, diabetes, chronic illness, or immunosuppressive therapy. Listeria monocytogenes (choice B) causes listeriosis and is not a notable cause of pneumonia. Spirillium minus (choice C) is a cause of rat-bite fever and is not a notable cause of pneumonia. Staphylococcus aureus (choice D) can cause pneumonia, but is easily cultured on routine media. Streptococcus pneumoniae (choice E) can cause pneumonia, but is easily cultured on routine media

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45.

A 27-year-old male is brought into the emergency room by the police, who found him walking aimlessly, shouting the names of former Presidents. Urine toxicology is negative, and the man appears to be oriented with respect to person, place, and time. He has had five similar admissions over the past year. Attempts to interview the patient are fruitless, as he seems easily derailed from his train of thought. A phone call to a friend listed in the chart provides the additional information that the man is homeless, and unable to care for himself. This patient is exhibiting the signs and symptoms of

Schizoaffective disorder
Schizoid personality disorder
Schizophrenia
Schizophreniform disorder
Schizotypal personality disorder

Correct Answer

A. Schizophrenia

Explanation

The patient is suffering from schizophrenia. The key to the diagnosis of psychosis is that there has been a marked decline in the level of functioning (i.e., the man is homeless and cannot care for himself). Although hallucinations or delusions are not mentioned in the case history, the presence of disorganized speech, grossly disorganized behavior, and the duration of symptoms (longer than six months) suggest a diagnosis of schizophrenia. In schizoaffective disorder (choice A), alterations in mood are present during a substantial portion of the illness. Although schizoid personality disorder (choice B) produces detachment from social relationships and is characterized by restriction of emotional expression, it is not accompanied by a marked decline in occupational functioning. Schizophreniform disorder (choice D) is characterized by schizophrenic-like symptoms, but the duration of symptoms is, by definition, less than six months. Schizotypal personality disorder (choice E) is characterized by eccentricities of behavior, odd beliefs or magical thinking, and difficulties with social and interpersonal relationships. Unlike schizophrenia, schizotypal personality disorder is not characterized by a formal thought disorder.

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46.

A young boy presents with failure to thrive. Biochemical analysis of a duodenal aspirate after a meal reveals a deficiency of enteropeptidase (enterokinase). The levels of which of the following digestive enzymes would be affected?

Amylase
Colipase
Lactase
Pepsin
Trypsin

Correct Answer

A. Trypsin

Explanation

Enteropeptidase, formerly called enterokinase, activates trypsinogen by limited proteolytic digestion to give trypsin. Trypsin is itself capable of activating trypsinogen, which produces a positive feedback effect. Trypsin also activates chymotrypsinogen (and several other proteolytic enzymes), so deficiency of enteropeptidase results in a severe deficiency of enzymes that digest protein. Amylase (choice A) aids in the breakdown of starches to oligosaccharides, maltose, and maltotriose. Colipase (choice B), along with other lipases, functions to digest fats. Lactase (choice C) is a brush-border disaccharidase that hydrolyzes the bond between galactose and glucose in lactose. Pepsin (choice D) is a proteolytic enzyme secreted in an inactive form (pepsinogen) by the chief cells of the stomach. Pepsinogen is activated by stomach acid, and so is not dependent on enteropeptidase. Pepsin alone will not replace the activities of other proteolytic enzymes, partly because food does not remain in the stomach for an extended period of time.

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47.

Which of the following drugs used in the treatment of noninsulin-dependent diabetes mellitus (NIDDM) has no effect on the secretion of insulin?

Acetohexamide
Chlorpropamide
Glyburide
Metformin
Tolbutamide

Correct Answer

A. Metformin

Explanation

Metformin is a drug that is often used in conjunction with oral hypoglycemic agents for the treatment of NIDDM. Its mechanism of action is two-fold: (1) it decreases the production of glucose in the liver; (2) it increases the uptake of glucose in the liver. Metformin has no effect on the secretion of pancreatic insulin. Acetohexamide (choice A) is an oral hypoglycemic agent that is a sulfonylurea derivative. It stimulates secretion of insulin from the pancreas. Chlorpropamide (choice B) is an oral hypoglycemic agent that is a sulfonylurea derivative. It stimulates secretion of insulin from the pancreas. Glyburide (choice C) is a sulfonylurea derivative that stimulates insulin secretion from the pancreas. Tolbutamide (choice E) is a sulfonylurea derivative that stimulates insulin secretion from the pancreas.

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48.

A 7-year-old boy is brought to a physician because of a nearly confluent, fine, erythematous, macular rash that is most pronounced on his trunk. He has had a mild fever for 36 hours, but does not appear very sick, and is happily playing when the pediatrician enters the examining room. Physical examination demonstrates a reddened throat with tonsillar exudates, enlarged cervical nodes including the occipital node, and questionable splenomegaly. The mother says that the boy has not been coughing, and no Koplik spots are noted. Which of the following is the most likely diagnosis?

Bullous pemphigoid
Dermatitis herpetiformis
Herpes simplex
Measles
Rubella

Correct Answer

A. Rubella

Explanation

This presentation (fine, nonblotchy, truncal rash in a not-very-ill child) is characteristic of rubella, or German measles. IgM specific for rubella can often be detected in serum within 1-2 days of developing the rash. The principal significance of this disease is that it can cause a devastating congenital infection characterized by ocular problems (cataracts, retinopathy, microphthalmos, glaucoma), cardiovascular problems (patent ductus arteriosus, ventricular septal defect, pulmonary stenosis), deafness, thrombocytopenic purpura, hepatosplenomegaly, CNS problems, and bony lesions. Bullous pemphigoid (choice A) produces large, tense blisters.
Dermatitis herpetiformis (choice B) causes recurrent crops of small vesicles or papules. Herpes simplex (choice C) is characterized by crops of vesicles on oral or genital sites. Measles (choice D) causes a blotchy, maculopapular erythematous rash that begins on the face and spreads downward. Patients with measles are usually much sicker than those with German measles, and Koplik spots maybe seen on the buccal mucosa

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49.

Administration of an experimental drug that acts on PNS myelin is shown to increase the space constant of an axon in a peripheral nerve. Action potentials traveling down the axon would be predicted to be

Faster
Larger
Slower
Smaller
Unchanged

Correct Answer

A. Faster

Explanation

The space constant of an axon reflects the amount of passive or electrotonic spread of current within an axon. The larger the space constant, the further the current can spread, allowing action potentials to propagate faster. This is why myelin increases the conduction velocity of action potentials down an axon. Conversely, demyelination decreases the space constant and slows action potential conduction.

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Hardest Trivia Questions Quiz On USMLE

Quiz Preview

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

During embryological development, hematopoiesis occurs in different organs at different times. Which of the following are the correct organs, in the correct sequence, at which hematopoiesis occurs embryologically?

A 37-year-old woman who was diagnosed with AIDS 3 years earlier is unable to work, is physically debilitated, and requests her physician to provide her with medications with which to take her own life. The most common emotional disorder that results in such requests by patients is

The blood from an 8-year-old boy was analyzed by flow cytometry . The exact number of B cells was counted. Which of the following cell surface markers was likely used to identify the B cells in this blood sample?

A 27-year-old white male presents with a 3-week history of several swollen and painful toes and knees. He has a past history of conjunctivitis. He also describes some low back stiffness that is more severe in the morning. Which of the following is the most likely diagnosis?

An otherwise healthy 3-year-old child is brought to the pediatrician with umbilicated, flesh-colored papules on his trunk. This condition is related to infection with which of the following viruses?

During a routine physical examination of a 74-year-old man, a physician palpates a large, pulsating mass in the lower abdomen. To which of the following is this mass most likely etiologically related?

Which of the following organisms is the most common cause of community-acquired pneumonia?

A child who has had abnormal development of the membranous bones has a broad skull with associated facial and dental anomalies. Which other bones are most likely to also be affected?

The cell in the center of the electron micrograph above is important in wound healing and plays a role in the pathological process underlying Dupuytren's contracture. Which of the following cell types is depicted?

After falling on his laterally outstretched arm, a patient suffered a dislocation of the glenohumeral joint. Which of the following nerves is most likely to have been injured from this dislocation?

A 70-year-old woman with a history of multiple small strokes reports to her physician that she has had multiple recent experiences that something or someone seemed very familiar, when in reality they were not familiar to her. This type of experience is called which of the following?

A woman presents to a dermatologist because she has lost almost all the hair on her body, including scalp hair, eyebrows, eyelashes, armpit, and groin hair, and the fine hairs on her body and extremities. Does she most likely have a variant of which of the following?

During embryological development, hematopoiesis occurs in different organs at different times. Which of the following are the correct organs, in the correct sequence, at which hematopoiesis occurs embryologically?

A 42-year-old female presents with a recent onset of fatigue, malaise, constipation, and a 12-pound weight gain. On examination, her thyroid is firm and enlarged. What laboratory test is most likely to confirm the expected diagnosis?

Which of the following renal structures is most medially located?

A Guatemalan child with a history of meconium ileus is brought to a clinic because of a chronic cough. The mother notes a history of respiratory tract infections and bulky, foul-smelling stools. After assessment of the respiratory tract illness, the physician should also look for signs of

A liver biopsy from a 54-year-old man shows many Mallory bodies. This finding is most suggestive of which of the following diseases?

A 38-year-old pregnant woman with a past medical history significant for chronic hypertension presents with a blood pressure of 158/105 mm Hg. Which of the following antihypertensive agents would be most suitable for initial therapy in this patient?

A surgical pathology specimen from a 24-year-old woman seen at a reproductive medicine clinic demonstrates a ciliated columnar epithelium. From which of the following locations in the female genital tract was the biopsy obtained?

A 54-year-old male with acute lymphocytic leukemia develops a blast crisis. He is treated with intensive systemic chemotherapy. Following treatment, the patient will be at increased risk for the development of

A 65-year-old man with mild heart failure is treated with a loop diuretic . A few days later the man complains of muscle weakness. Laboratory results are shown below. Arterial PCO2: 48 mm Hg Arterial pH: 7.49 Plasma HCO3-: 35 mEq/L Which of the following is most likely decreased in this man?

Which of the following hormones is secreted by anterior pituitary cells that stain with acidic dyes?

A 45-year-old homeless man has a chronic cough, a cavitary lesion of the lung, and is sputum positive for acid-fast bacilli. Which of the following is the principle form of defense by which the patient's body fights this infection?

Which of the following would shift the oxygen-hemoglobin dissociation curve to the right?

A 27-year-old woman is giving birth. During the birth, the placental membranes tear and amniotic fluid is expressed into a lacerated cervical vein. Which of the following is the woman most likely to experience immediately following this event?

A young boy presents with failure to thrive. Biochemical analysis of a duodenal aspirate after a meal reveals a deficiency of enteropeptidase (enterokinase). The levels of which of the following digestive enzymes would be affected?

Which of the following drugs used in the treatment of noninsulin-dependent diabetes mellitus (NIDDM) has no effect on the secretion of insulin?

Administration of an experimental drug that acts on PNS myelin is shown to increase the space constant of an axon in a peripheral nerve. Action potentials traveling down the axon would be predicted to be