NBME 13 Section 4 (Qst 1-50)

Sorbitol is the most likely aberrant metabolite of glucose responsible for the formation of milky opacity in the lenses of the eyes. In diabetes mellitus, excess glucose in the blood is converted to sorbitol by the enzyme aldose reductase. Sorbitol accumulates in the lens and draws water into it, causing swelling and opacity. This condition is known as diabetic cataracts and can lead to vision loss.

Wikipedia http://en.wikipedia.org/wiki/Myasthenia_gravis
Myasthenia gravis (from Greek μύς "muscle", ἀσθένεια "weakness", and Latin: gravis "serious"; abbreviatedMG) is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigability. It is anautoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptorsat the postsynaptic neuromuscular junction,[1] inhibiting the excitatory effects of the neurotransmitteracetylcholine on nicotinic receptors throughout neuromuscular junctions. Myasthenia is treated medically withacetylcholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. The diseaseincidence is 3–30 cases per million per year and rising as a result of increased awareness.[2] MG must be distinguished from congenital myasthenic syndromes that can present similar symptoms but offer no response to immunosuppressive treatments.

B. Botulism would be more acute and lead to flaccid paralysis
C. CRP is a good measure of inflammation, however it is unspecific.
D. Rapid Plasma Reagin test is used to detect antibodies against Treponema Pallidum which is the causative agent in syphilis.
E. Rheumatoid Factor is an antibody active against the Fc portion of immunoglobulins(Ig’s). This level will be elevated in diseases such as Rheumatoid arthritis and Sjogren’s Syndrome.

Struvite stones
About 10–15% of urinary calculi are composed of struvite (ammonium magnesium phosphate, NH4MgPO4·6H2O).[38] Struvite stones (also known as "infection stones", urease or triple-phosphate stones), form most often in the presence of infection by urea-splitting bacteria. Using the enzyme urease, these organismsmetabolize urea into ammonia and carbon dioxide. This alkalinizes the urine, resulting in favorable conditions for the formation of struvite stones. Proteus mirabilis, Proteus vulgaris, and Morganella morganii are the most common organisms isolated; less common organisms include Ureaplasma urealyticum, and some species ofProvidencia, Klebsiella, Serratia, and Enterobacter. These infection stones are commonly observed in people who have factors that predispose them to urinary tract infections, such as those with spinal cord injury and other forms of neurogenic bladder, ileal conduit urinary diversion, vesicoureteral reflux, and obstructive uropathies. They are also commonly seen in people with underlying metabolic disorders, such as idiopathic hypercalciuria, hyperparathyroidism, and gout. Infection stones can grow rapidly, forming large calyceal staghorn (antler-shaped) calculi requiring invasive surgery such as percutaneous nephrolithotomy for definitive treatment.[38]

The most likely diagnosis for this patient is mucormycosis. Mucormycosis is a fungal infection caused by the Mucorales order of fungi. It typically affects immunocompromised individuals, such as those with uncontrolled diabetes. The presence of a black eschar on the nasal mucosa is a characteristic finding in mucormycosis. Proptosis of the left eye and inability to move the eye can be attributed to the invasive nature of the infection, which can spread to the orbit and surrounding structures. Fever is a common systemic symptom seen in mucormycosis.

The patient's symptoms of shortness of breath, night sweats, weight loss, and fatigue, along with the findings of enlarged hilar lymph nodes and nodular infiltrates in both lungs on chest X-ray, are consistent with sarcoidosis. The negative PPD skin test and absence of organisms on staining suggest that tuberculosis is unlikely. Sarcoidosis is characterized by the formation of noncaseating granulomas with giant cells, which were seen on examination of lung tissue obtained on biopsy. Therefore, sarcoidosis is the most likely diagnosis in this case.

The patient's presentation of a markedly increased serum beta-human chorionic gonadotropin (beta-hCG) concentration, a uterus consistent in size with a 20-week gestation, and the presence of echogenic material within the endometrial cavity but no fetus suggests a molar pregnancy, specifically a complete hydatidiform mole. In a complete mole, there is proliferation of trophoblastic tissue, which leads to the characteristic findings seen in this patient. The other answer choices, such as allantois, blastocysts, decidua basalis, and decidua capsularis, are not associated with the specific findings seen in a molar pregnancy.

The most likely diagnosis in this case is Gilbert syndrome. This is supported by the patient's mild scleral icterus, which is a common finding in this condition. Gilbert syndrome is a benign, inherited disorder characterized by a deficiency of the enzyme glucuronyl transferase, leading to impaired bilirubin conjugation and mild unconjugated hyperbilirubinemia. It is often asymptomatic but can be triggered by factors such as fasting, stress, and certain medications, which may explain the patient's symptoms. The absence of other symptoms such as clay-colored stools or dark urine, as well as the lack of risk factors for other liver diseases, further support this diagnosis.

The patient's symptoms of pain, swelling, and stiffness in both hands, along with the presence of nodules on the extensor surfaces of the arms and tenderness and swelling of the metacarpophalangeal and proximal interphalangeal joints, suggest the presence of rheumatoid arthritis (RA). Pannus formation is a characteristic feature of RA and refers to the abnormal growth of synovial tissue in the joints. This pannus tissue can invade and destroy cartilage and bone, leading to joint deformity and functional impairment. Therefore, pannus formation is the most likely pathologic process affecting the patient's joints in this case.

Lippincott’s Pharmacology E
Triptans: This class of drugs includes sumatriptan [SOO-ma-triptan], naratriptan [NAR-a-trip-tan], rizatriptan [rye-za-TRIP-tan], eletriptan [EH-leh-trip-tan], almotriptan [AL-moh-trip-tan], frovatriptan (frova-TRIP-tan), and zolmitriptan [zole-ma-TRIP-tan]. These agents rapidly and e!ectively abort or markedly reduce the severity of migraine headaches in about 70 percent of patients. The triptans are serotonin agonists, acting at a subgroup of serotonin receptors found on small peripheral nerves that innervate the intracranial vasculature. The nausea that occurs with dihydroergotamine and the vasoconstriction caused by ergotamine (see below) are much less pronounced with the triptans, particularly rizatriptan and zolmitriptan. Sumatriptan is given subcutaneously, intranasally, or orally. Zolmitriptan is available orally and by nasal spray. [Note: All other agents are taken orally.] The onset of the parenteral drug (which is indicated for treatment of cluster headaches) is about 20 minutes, compared with 1 to 2 hours when the drug is administered orally. The drug has a short duration of action, with an elimination half-life
of 2 hours. Headache commonly recurs within 24 to 48 hours after a single dose of drug, but in most patients, a second dose is e!ective in aborting the headache. Rizatriptan and eletriptan are modestly more efective than sumatriptan, the prototype drug, whereas, naratriptan and almotriptan are better tolerated. Frovatriptan is the longest-acting triptan, with a half-life of more than 24 hours. Individual responses to triptans vary, and more than one drug trial may be necessary before treatment is successful. Significant elevation of blood pressure and cardiac events have been reported with triptan use. Therefore, triptans should not be administered to patients with risk factors for coronary artery disease without performing a cardiac evaluation prior to administration. Other adverse events with the use of triptans include pain and pressure sensations in the chest, neck, throat, and jaw.

The patient's symptoms of cramping abdominal pain, diarrhea, and weight loss, along with a history of swimming in lakes and hiking in the mountains, suggest a possible parasitic infection. Microscopic examination of the stool for ova (eggs) and parasites is the most appropriate diagnostic test to identify the causal organism in this patient's condition. This test can help identify the presence of parasites such as Giardia lamblia, which is commonly associated with recreational water activities and can cause symptoms similar to those described by the patient.

The risk for this couple's next child to have Tay-Sachs disease is 25%. Tay-Sachs disease is an autosomal recessive disorder, meaning that both parents must be carriers of the gene mutation in order for the child to inherit the disease. Since both the woman and the man have a family history of Tay-Sachs disease, it is likely that they are carriers. When two carriers have a child, there is a 25% chance that the child will inherit the disease.

The patient's symptoms and laboratory findings suggest a diagnosis of hypogonadotropic hypogonadism, which is characterized by decreased libido, erectile dysfunction, decreased facial hair growth, and low testosterone levels. The presence of a pituitary lesion on MRI further supports this diagnosis. Bromocriptine is a dopamine agonist that inhibits prolactin secretion, which can be elevated in patients with pituitary tumors. By reducing prolactin levels, bromocriptine can restore normal gonadotropin secretion and stimulate testosterone production, thereby improving the patient's symptoms of hypogonadism.

The positive predictive value (PPV) of a test is the probability that a positive result is truly positive. In this case, as the prevalence of prostate cancer increases in the second population, the likelihood of a positive result being a true positive also increases. This is because a higher prevalence means there are more true positives in the population, increasing the chances of a positive result being a true positive. Therefore, the PPV of the test is expected to increase as the prevalence increases.

Staphylococcus aureus is the most likely causal organism in this patient. The presence of a tunneled central venous catheter and a vegetation on the tricuspid valve suggests infective endocarditis, which is commonly caused by Staphylococcus aureus in patients with end-stage renal disease and hemodialysis. The history of fever and shaking chills further supports the diagnosis.

Interleukin-1 (IL-1) is most likely causing this patient's fever and leukocytosis. IL-1 is a pro-inflammatory cytokine that is released by activated macrophages and other cells in response to infection or tissue injury. It acts on the hypothalamus to increase body temperature, resulting in fever. IL-1 also stimulates the production of acute phase reactants, including leukocytes, leading to leukocytosis. The patient's symptoms of fever and elevated leukocyte count, along with the presence of cramping periumbilical pain that shifts to the right lower quadrant, suggest acute appendicitis, which is commonly associated with an inflammatory response mediated by IL-1.

The patient's presentation of skin blistering and crusted denuded areas, along with the biopsy findings of intraepidermal vesicle formation and deposits of IgG on keratinocytes, suggests a diagnosis of pemphigus vulgaris. Pemphigus vulgaris is an autoimmune disorder that affects desmosomes, which are specialized cell junctions that provide strong adhesion between epithelial cells. Disruption of desmosomes leads to separation of the epidermis, resulting in the formation of blisters. Therefore, desmosomes (maculae adherentes) are most likely involved in the skin disorder in this patient.

After recovering from a stroke, individuals may experience a range of emotional and psychological changes. The man in this scenario lives alone, which can contribute to feelings of isolation and loneliness. Major depressive disorder is a psychiatric disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest in activities. Given the man's age, recent stroke, and living situation, he is at an increased risk for developing major depressive disorder.

The patient's presentation of progressive facial abnormalities, slow growth, coarse facial features, hepatosplenomegaly, and joint stiffness are consistent with a lysosomal storage disorder known as mucopolysaccharidosis (MPS). The increased urine concentrations of dermatan sulfate and heparan sulfate further support this diagnosis. The most likely enzyme deficiency causing these findings is iduronate sulfatase, which is responsible for the degradation of dermatan sulfate and heparan sulfate. This enzyme deficiency leads to the accumulation of these substances in various tissues, resulting in the clinical manifestations observed in the patient.

The patient in this case has a BMI of 29 kg/m2, which falls into the category of overweight. He also has a protuberant abdomen and increased waist circumference, indicating central obesity. Additionally, his blood pressure is elevated at 140/90 mm Hg. These findings suggest that the patient may have metabolic syndrome, a cluster of conditions that increase the risk of heart disease, stroke, and diabetes. The most likely set of additional laboratory findings in this patient would be elevated triglyceride levels, decreased HDL cholesterol levels, and increased fasting plasma glucose levels, as seen in option C. These findings would further support the diagnosis of metabolic syndrome.

Based on the patient's symptoms of flushing, hypotension, and crampy diarrhea, along with the presence of a heart murmur and hepatomegaly, the most likely site of a primary neoplasm in this patient is the small intestine. These symptoms are consistent with a condition called carcinoid syndrome, which is commonly caused by a neuroendocrine tumor (carcinoid tumor) in the small intestine. The tumor secretes serotonin and other vasoactive substances, leading to the symptoms described.

The most appropriate response by the emergency department physician is to encourage the patient to make an appointment with his physician to communicate his concerns. This response acknowledges the patient's complaints and suggests a direct approach to address them. It allows the patient to express his concerns and potentially resolve any issues with his physician.

The most appropriate initial statement by the physician regarding this patient's breast finding is "This is a common condition for teenage boys and should resolve in time." This is because the patient's presentation is consistent with physiologic gynecomastia, which is a common occurrence during puberty. It is characterized by the development of a palpable breast bud in one or both breasts, usually resolving within 6 months to 2 years. The absence of any concerning findings, such as family history of breast cancer or other symptoms, suggests that this is a benign condition that does not require further testing or intervention.

Metformin is a medication commonly used to treat type 2 diabetes. In overdose, it can cause a condition called lactic acidosis, which is characterized by an increased level of lactic acid in the blood. Lactic acidosis is a potentially life-threatening condition that can lead to metabolic acidosis and organ dysfunction. In this scenario, the 3-year-old girl consumed a large number of metformin tablets, putting her at risk for developing lactic acidosis. The other serum abnormalities listed in the answer choices are not typically associated with metformin overdose.

The correct answer is endothelium because a hemangioma is a benign growth that originates from the endothelial cells, which line the blood vessels. The raised, red area on the newborn's neck is likely a result of abnormal proliferation of these endothelial cells.

The suspensory ligament is most likely affected in this patient. The patient's symptoms of acute, sharp, right-sided lower abdominal pain that radiates to her back, along with an enlarged right ovary and decreased adnexal flow on Doppler ultrasonography, suggest ovarian torsion. Ovarian torsion occurs when the ovary twists on its suspensory ligament, leading to compromised blood flow and subsequent ischemia. This condition typically presents with sudden onset of severe pain and can result in ovarian infarction if not promptly treated.

The correct answer is Myasthenic (Lambert-Eaton) syndrome. This is supported by the description of a 42-year-old man with an autoimmune disorder and proximal muscle weakness of the lower extremities. Myasthenic (Lambert-Eaton) syndrome is a neuromuscular disorder characterized by muscle weakness and fatigue, particularly in the proximal muscles. It is caused by an autoimmune attack on the presynaptic voltage-gated calcium channels at the neuromuscular junction, leading to impaired release of acetylcholine and subsequent muscle weakness.

This patient's symptoms and findings are consistent with a mitochondrial disorder, specifically a mitochondrial encephalomyopathy. The presence of ragged red fibers on muscle biopsy is a characteristic finding in mitochondrial disorders. Oxidative phosphorylation is the process by which ATP is generated in the mitochondria, and impairment of this process can lead to a decrease in ATP production, resulting in the symptoms seen in this patient. Fatty acid oxidation, gluconeogenesis, glycolysis, and the pentose phosphate pathway are not directly involved in ATP production in the mitochondria.

The patient's history of decreasing urine output and recent use of gentamicin suggests the possibility of acute tubular necrosis (ATN), a common cause of acute kidney injury. ATN primarily affects the proximal tubules of the nephron. Therefore, histologic examination of the patient's kidneys would most likely show necrotic cells in the proximal tubule.

This patient's symptoms, including fever, severe rib pain, and a history of similar symptoms in her paternal aunt and uncle, are consistent with sickle cell disease. Sickle cell disease is caused by a mutation in the hemoglobin beta (B) chain, resulting in the substitution of valine for glutamic acid at position 6. This amino acid substitution leads to the polymerization of hemoglobin under hypoxic conditions, causing the characteristic sickle shape of red blood cells. This can lead to vaso-occlusive crises and tissue ischemia, explaining the patient's symptoms.

Gemfibrozil is known to inhibit the cytochrome P450 enzyme system, which is responsible for the metabolism of many drugs, including simvastatin. By inhibiting the metabolism of simvastatin, gemfibrozil can increase its concentration in the body, leading to a higher risk of adverse effects. In this case, the patient's myalgia is likely a result of the increased concentration of simvastatin due to the inhibition of its metabolism by gemfibrozil.

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The patient's symptoms, such as weakness, atrophy of hand muscles, hyperreflexia, and fasciculations, suggest a motor neuron disease. Difficulty swallowing, also known as dysphagia, is a common symptom in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). In ALS, the degeneration of upper and lower motor neurons leads to muscle weakness and atrophy, including the muscles involved in swallowing. Therefore, difficulty swallowing is the most likely finding in this patient.

¢Lymphocytosis
¢Blood smear: Atypical lymphocytes (T cells) = mononuclear cells
—More than 10% atypical lymphocytes
¢ Detection of EBV DNA or RNA by hybridization
¢ In situ methods for visualization of infected cells.
—Some prep on the cell and
¢Serology: Heterophile antibody test
***ATYPICAL LYMPHOCYTES are enlarged lymphocytes that have abundant cytoplasm, vacuoles, and indentations of the cell membrane , CD8+ cells predominate among the atypical lymphocytes.
T cells are activated by infected B cells: TheT cells appear as atypical lymphocytes called Downey cells

The most likely defect in this patient is a ventricular septal defect (VSD). The loud, harsh, high-pitched holosystolic murmur that radiates over the precordium and the palpable thrill at the left sternal border are characteristic findings of a VSD. A VSD is a congenital heart defect where there is an abnormal opening between the ventricles, allowing blood to flow from the left ventricle to the right ventricle. This results in a left-to-right shunt and the murmur and thrill are caused by the increased flow of blood across the defect.

The ability to administer bevacizumab, despite it being a foreign protein, is most likely a result of the agent being a humanized antibody. Humanized antibodies are designed to minimize the immunogenic response by incorporating human sequences into the antibody structure, reducing the likelihood of an immune response against the drug. This allows for better tolerance and prolonged use of the medication in patients.

The monoclonal antibody against the platelet IIb/IIIa receptor is given to prevent binding of fibrinogen to platelets. Fibrinogen is an essential protein for platelet aggregation and clot formation. By blocking the binding of fibrinogen to platelets, the antibody helps to prevent further clot formation and reduce the risk of thrombus formation. This is important in the management of the patient's angina pectoris, as it helps to prevent the progression of his symptoms and reduce the risk of myocardial infarction.

The correct answer is "Anterior to the sternocleidomastoid muscle." Incomplete fusion during embryonic development suggests the presence of a branchial cleft cyst. Branchial cleft cysts are derived from the branchial apparatus, which is a series of arches and clefts that form during embryogenesis. The most common type of branchial cleft cyst is a second branchial cleft cyst, which presents as a painless, slowly enlarging mass on the lateral side of the neck, anterior to the sternocleidomastoid muscle. These cysts often have a cutaneous surface opening, and their location and characteristics are consistent with the findings described in the question.

The statistical power of a study is the probability of correctly rejecting the null hypothesis when it is false. In this case, Trial X has a statistical power of 0.6, while Trial Y has a statistical power of 0.9. Since the statistical power is directly related to the likelihood of a type II error (failing to reject the null hypothesis when it is false), it can be concluded that the likelihood of a type II error is greater in Trial X than in Trial Y.

The most likely cause of this patient's orthostatic hypotension is hypovolemia. The patient's symptoms began after skiing at a high altitude, which can cause fluid loss and dehydration. Additionally, the patient has been taking a carbonic anhydrase inhibitor, which can lead to increased urinary bicarbonate excretion and subsequent volume depletion. The low blood pressure while standing further supports the diagnosis of hypovolemia. High-altitude sickness, hypoxia, impaired sympathetic nerve activity, and respiratory alkalosis are less likely causes in this scenario.

Erythromycin interferes with translocation in protein synthesis. Translocation is the process in which the ribosome moves along the mRNA strand, allowing for the addition of the next amino acid to the growing peptide chain. By interfering with this process, erythromycin disrupts protein synthesis and inhibits the growth of bacteria, including group A Streptococcus. This is why the boy's condition improves after starting treatment with erythromycin.

The presence of a mature core in the virus is an important step in the replication of HIV. A mature core is formed when the viral protease cleaves the viral polyprotein into its individual components. Therefore, if there is a lack of a mature core, it suggests that the compound is specifically inhibiting the protease activity, preventing the cleavage of the polyprotein and the formation of a mature core. This finding indicates that the compound is working specifically as a protease inhibitor.

The sequence AATAAA is known as the polyadenylation signal sequence, which is involved in the cleavage and polyadenylation of mRNA. Cleavage and polyadenylation is an important step in mRNA processing, where the pre-mRNA is cleaved and a poly(A) tail is added to the 3' end. This poly(A) tail protects the mRNA from degradation and is important for mRNA stability and translation. In this case, the point mutation in the sequence AATAAA leads to a decrease in the amount of mRNA for B-globin, indicating a defect in the cleavage and polyadenylation process.

Myasthenia gravis is the most likely underlying cause of this patient's condition. Myasthenia gravis is an autoimmune disorder characterized by muscle weakness and fatigue, which can affect the muscles involved in breathing. The patient's symptoms of progressive shortness of breath and difficulty taking a long, deep breath are consistent with respiratory muscle weakness. The arterial blood gas analysis shows an elevated Pco2 and a decreased Po2, indicating respiratory acidosis and impaired gas exchange, which can occur in myasthenia gravis due to respiratory muscle weakness. The pulmonary function testing findings of decreased vital capacity, tidal volume, and expiratory reserve volume further support the diagnosis of myasthenia gravis.

The correct answer is the glucagon receptor. The fact that administration of glucagon does not correct the hypoglycemia suggests that there is a problem with the receptor that normally binds to glucagon. This receptor is responsible for activating adenylyl cyclase, which in turn stimulates the production of glucose. Since administration of epinephrine, which acts through a different pathway, results in an increase in serum glucose concentration, it indicates that the problem lies specifically with the glucagon receptor.

A low-calorie diet is most likely to be effective in decreasing this patient's risk for type 2 diabetes mellitus. This is because obesity is a major risk factor for developing type 2 diabetes, and this patient has a BMI that indicates obesity. By reducing calorie intake, the patient can achieve weight loss, which can improve insulin sensitivity and reduce the risk of developing diabetes. Additionally, a low-calorie diet can help control blood sugar levels and prevent excessive weight gain, further reducing the risk of diabetes.

The process shown in the photograph is most likely associated with an increase in Interleukin-1 (IL-1). IL-1 is a pro-inflammatory cytokine that plays a role in bone resorption. It stimulates the activation of osteoclasts, which are responsible for breaking down bone tissue. In conditions such as osteoporosis or chronic inflammation, there can be an increase in IL-1 levels, leading to increased bone resorption and potentially resulting in structural changes in the vertebral column, as seen in the photograph.

Cervical cancer and the human papillomavirus type 16 E6 protein are most likely to produce the highest antibody titer. This is because cervical cancer is caused by the human papillomavirus (HPV) type 16, and the E6 protein is a viral protein produced by HPV 16. The immune response against the E6 protein in cervical cancer is expected to be strong, leading to a high antibody titer.

The patient's symptoms, along with the presence of bright red venous blood and elevated carboxyhemoglobin saturation, indicate carbon monoxide (CO) poisoning. CO binds to hemoglobin with a higher affinity than oxygen, leading to impaired oxygen delivery to tissues. In the electron transport pathway, complex IV (cytochrome c oxidase) is primarily affected by CO poisoning, as it is responsible for transferring electrons to oxygen to form water. Therefore, the correct answer is E.

The patient's symptoms of numbness, loss of touch graphesthesia, and loss of two-point discrimination in the left hand suggest a sensory deficit. The sensory cortex is responsible for processing sensory information, including touch and discrimination. Therefore, a lesion in the sensory cortex, which is located in the parietal lobe, would most likely cause these symptoms. Answer B shows the parietal lobe, which is the correct location for the lesion.