NBME 13 Section 3 (Qst 1-50)

The patient's symptoms, such as difficulty breathing, excess salivation, and diarrhea, suggest that he is experiencing symptoms of organophosphate poisoning. Atropine is the most appropriate treatment for organophosphate poisoning as it acts as an antidote by blocking the effects of acetylcholine, the neurotransmitter affected by organophosphates. Atropine can help reverse the excessive stimulation of the parasympathetic nervous system caused by organophosphates, relieving symptoms such as excessive salivation and sweating.

The patient's symptoms of intermittent heartburn, especially after lying down and accompanied by a bitter taste, suggest gastroesophageal reflux disease (GERD). The patient's obesity and alcohol consumption are contributing factors to GERD. Omeprazole, a proton pump inhibitor, is the most appropriate drug for this patient as it reduces gastric acid secretion and provides relief from heartburn. Weight loss and decreased alcohol consumption are also important lifestyle modifications to manage GERD. Loperamide is an antidiarrheal, misoprostol is a prostaglandin analog used for preventing gastric ulcers, prochlorperazine is an antiemetic, and sucralfate is a mucosal protective agent, none of which are indicated for GERD.

The patient's symptoms of chronic abdominal pain, weight loss, and malodorous stools, along with a pruritic rash, are consistent with dermatitis herpetiformis (DH). DH is a skin manifestation of celiac disease, which is an autoimmune disorder triggered by gluten ingestion. The fact that the patient's mother also has a similar illness controlled by restricting wheat, barley, and rye in her diet further supports the diagnosis of DH. Bullous pemphigoid, epidermolysis bullosa, erythema nodosum, and pemphigus vulgaris are unrelated conditions and do not fit with the patient's symptoms.

The most likely mechanism of the newborn's condition is hypertrophy of the pyloric sphincter. This condition, known as pyloric stenosis, is characterized by the thickening and narrowing of the pyloric sphincter, which leads to difficulty in food passing from the stomach to the small intestine. The persistent nonbilious projectile vomiting and prominent peristalsis are typical clinical manifestations of pyloric stenosis. Metabolic alkalosis is also commonly seen in this condition due to the loss of hydrochloric acid through vomiting.

The most appropriate response to encourage the patient to quit smoking is to ask if they have ever thought about quitting. This response shows empathy and allows the patient to reflect on their smoking habit without being judgmental or forceful. It opens up a conversation about quitting smoking and allows the physician to provide information and support to the patient.

The description of the murmur in this patient is consistent with a systolic ejection murmur, which is characteristic of aortic stenosis. The murmur is best heard in the second interspace at the right sternal border and is transmitted to the carotid arteries. The timing of the murmur, beginning immediately after S1 and ceasing before S2, is also consistent with aortic stenosis. Atrial septal defect, mitral regurgitation, pulmonary regurgitation, and tricuspid stenosis would not typically present with this specific pattern of murmur.

The most likely causal organism in this scenario is Group A Streptococcus, which produces a toxin called streptococcal pyrogenic exotoxin A (SpeA). This toxin causes ADP-ribosylation of elongation factor-2 (EF-2). ADP-ribosylation of EF-2 inhibits protein synthesis, leading to the characteristic symptoms of this infection, such as sore throat, fever, and difficulty swallowing. Acetylcholinesterase is not the target in this case, and the other options are not associated with the causal organism or its toxin.

The correct answer is hyperuricemia. In this case, the patient's self-mutilating behavior, along with the presence of spasticity, chorea, and mutilation of the digits, suggests the diagnosis of Lesch-Nyhan syndrome. This is a rare genetic disorder that results in the deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT), leading to the accumulation of uric acid. Hyperuricemia is a hallmark feature of this condition. Laboratory studies would likely show elevated levels of uric acid, confirming the diagnosis.

The most likely process responsible for the large irregular area in the left ventricle is coagulation necrosis. Coagulation necrosis occurs when there is a lack of blood supply to the tissue, leading to cell death. In this case, the complete occlusion of the left coronary artery would have caused ischemia and subsequent necrosis of the tissue in the left ventricle. The description of the area being soft and pale is consistent with coagulation necrosis.

The patient's symptoms of sneezing, coughing, watery eyes, and the development of a red rash immediately after mowing the lawn suggest an allergic reaction. The presence of soft, raised, pruritic, erythematous lesions with wheal and flare eruptions is characteristic of a type I (immediate) hypersensitivity reaction. Type I hypersensitivity reactions involve the release of histamine and other mediators from mast cells and basophils, resulting in the symptoms seen in this patient.

Based on the information provided, the 59-year-old man's smoking history is a significant risk factor for developing squamous cell carcinoma of the larynx. Smoking is strongly associated with the development of squamous cell carcinomas in various parts of the body, including the larynx. Therefore, it is most likely that the examination of the tissue obtained on biopsy of the ulcerated laryngeal neoplasm will show squamous cell carcinoma.

Although it does not produce any exotoxins, Neisseria gonorrhoeae has a wide range of virulence determinants. The first stages of infection, which includes adherence and invasion, are mediated by surface components. The bacterium first attaches to epithelial cells by means of its fimbriae, SPECIFICALLY N-METHYLPHENYLALANINE (TYPE IV) PILI, with the main subunit PilE. After initial attachment, the bacteria enter a second stage of binding mediated by the outer membrane protein P.II (also known as Opa) which is needed for tight binding and invasion of epithelial cells. Also, P.II from one bacterium will bind to LOS of an adjacent bacterium, which allows for the construction of a small colony that may function similarly to a biofilm. Neisseria gonorrhoeae also produces an IgA1 protease that may take part in the colonization stage.
The outer membrane porin of N. gonorrhoeae P.I (also known as Por) is equivalent to the ompC and ompF porins of E. coli. They are involved in the passage of solutes through the outer membrane. However, P.I apparently has a role in virulence that allows the gonococci to survive inside of phagocytes. Purified P.I has also been shown to inhibit the ability of phagocytes to kill ingested bacteria. The lipooligosaccharide (LOS) is thought to be responsible for most of the symptoms of gonorrhea. Gonococcal LOS triggers an intense inflammatory response. The activation of complement, attraction and feeding by phagocytes, and the lysing of the phagocytes themselves, contributes to the purulent discharge. The local production of TNF is thought to be the main cause of damage to the fallopian tubes. In addition, in strains that cause systemic infection, LOS binds sialic acid from the serum forming a microcapsule of sialylated LOS, which allows the gonococci to resist the host immune response and serum bactericidal reaction

The reason for including IL-2 in the regimen is to stimulate T lymphocytes. IL-2 is a cytokine that plays a crucial role in the activation and proliferation of T lymphocytes, which are important for the immune response against cancer cells. By stimulating T lymphocytes, IL-2 can enhance the immune system's ability to target and destroy cancer cells, potentially improving the outcome of the treatment.

The patient is presenting with urinary frequency and urgency, difficulties with walking, conversation, and memory, and a wide-based, shuffling gait. These symptoms, along with the marked enlargement of the ventricles seen on the CT scan, are consistent with normal-pressure hydrocephalus (NPH). NPH is characterized by the accumulation of cerebrospinal fluid in the ventricles, leading to increased pressure and enlargement of the ventricles. This can cause a triad of symptoms including urinary incontinence, gait disturbance, and cognitive decline. Parkinson's disease can also present with gait disturbance, but it is less likely in this case as the patient does not have any other characteristic symptoms of Parkinson's, such as tremor or rigidity.

The patient's presentation of macroglossia and enlargement of the anterior neck at the midline is consistent with a thyroglossal duct cyst. The thyroglossal duct is a structure that connects the developing thyroid gland to the tongue during embryonic development. Normally, the thyroglossal duct obliterates and disappears by birth, but in some cases, it persists and can give rise to cysts. These cysts typically present as painless, midline neck masses that move with swallowing or protrusion of the tongue. CT scan findings of a well-defined, cystic structure further support the diagnosis of a thyroglossal duct cyst.

Analysis of class I MHC allele expression would be most appropriate for the patient's two children to evaluate their susceptibility to ankylosing spondylitis. Ankylosing spondylitis is strongly associated with the human leukocyte antigen (HLA)-B27 allele, a class I MHC allele. Therefore, analyzing the expression of class I MHC alleles can help determine if the children have inherited the HLA-B27 allele and are at an increased risk of developing ankylosing spondylitis.

The patient's presentation is consistent with iron deficiency anemia. The red, swollen, tender tongue and angular stomatitis are characteristic findings of iron deficiency. Spoon-shaped nails, known as koilonychia, are also commonly seen. Additionally, the decreased hemoglobin and mean corpuscular volume support the diagnosis of iron deficiency anemia. Vitamin B12 deficiency can cause similar symptoms, but it typically presents with neurological symptoms as well. Folic acid deficiency can cause megaloblastic anemia, but it does not typically cause the specific findings mentioned in the question. Sickle cell disease and vitamin B1 deficiency are not associated with the specific findings mentioned in the question.

The patient's history of recurrent urinary tract infections and the presence of 3+ blood, 1+ leukocytes, and few bacteria in the urinalysis suggest an infection-related stone. Struvite stones are commonly associated with urinary tract infections caused by urease-producing bacteria, which can hydrolyze urea to ammonia and increase the urine pH. The alkaline urine pH promotes the precipitation of magnesium ammonium phosphate crystals, leading to the formation of struvite stones. Therefore, the large calculus filling the right renal pelvis in this patient is most likely composed of struvite.

The patient's symptoms of burning pain with urination, uterine prolapse, and mild increase in leukocytes on urinalysis suggest a urinary tract infection (UTI). The ultrasonography findings of bilateral dilation of the renal collecting system indicate hydronephrosis, which is commonly seen in cases of UTI involving the upper urinary tract. Pyelonephritis, which is a bacterial infection of the kidneys, is the most likely diagnosis in this case. Therefore, the patient is at greatest risk for pyelonephritis.

The patient's symptoms and physical examination findings are consistent with hypothyroidism. Hypothyroidism can cause weight gain, irregular menstrual periods, constipation, fatigue, difficulty with concentration and memory, dry skin, and decreased reflexes. The low blood pressure and high cholesterol are also associated with hypothyroidism. Thyroid-stimulating hormone (TSH) is the most appropriate test to confirm the diagnosis of hypothyroidism. In this case, an elevated TSH level would indicate primary hypothyroidism, where the thyroid gland is not producing enough thyroid hormone.

Dextromethorphan is the most likely drug for short-term cough suppressant treatment in this patient. It is a commonly used over-the-counter cough suppressant that does not cause constipation and has a low potential for substance abuse. Codeine, hydromorphone, oxycodone, and tramadol are opioids that can cause constipation and have a higher potential for substance abuse, making them less suitable for this patient. The patient's lack of smoking history, absence of asthma or chronic pulmonary disease, and normal physical examination findings further support the use of dextromethorphan as the appropriate choice.

The patient's symptoms of shortness of breath and wheezing, which occur after taking certain over-the-counter medications containing aspirin, suggest that he may have aspirin-exacerbated respiratory disease (AERD). AERD is characterized by an excessive production of leukotrienes, which are inflammatory mediators involved in the pathogenesis of asthma. This excessive production is due to the dysregulation of the arachidonic acid pathway, leading to increased production of leukotrienes and decreased production of prostaglandins. The absence of eosinophilia and normal IgE levels in this patient further support the diagnosis of AERD. Therefore, the excessive production of leukotrienes is the most likely cause of this patient's symptoms.

Reactivating the genes that code for the chains of fetal hemoglobin would increase the production of fetal hemoglobin. Fetal hemoglobin has a higher affinity for oxygen compared to adult hemoglobin. Therefore, this treatment is most likely to increase the affinity of hemoglobin for oxygen.

The most likely causal organism in this case is Pneumocystis jiroveci (formerly P. carinii). This is indicated by the patient's seropositivity for HIV, which puts them at a higher risk for opportunistic infections. Pneumocystis jiroveci is a common opportunistic infection in individuals with HIV and can cause a nonproductive cough and diffuse interstitial infiltrate on chest x-ray. The silver stain of the lung biopsy specimen would likely show characteristic cysts or trophozoites of Pneumocystis jiroveci, confirming the diagnosis.

The most likely cause of the hip abnormality in this 19-year-old woman is aseptic necrosis. Aseptic necrosis, also known as avascular necrosis, is the death of bone tissue due to a lack of blood supply. It can be caused by corticosteroid use, which this patient has been taking for her refractory inflammatory bowel disease. The x-ray findings of collapse of the superior half of the right femoral head with preservation of the articular cartilage are consistent with aseptic necrosis. Ankylosing spondylitis, gouty arthritis, multiple myeloma, and septic arthritis are less likely causes in this clinical scenario.

Lymph node involvement by cells originating in the lesion is the best predictor of prognosis in this case. Lymph node involvement indicates that the cancer cells have spread beyond the breast and into the lymphatic system, increasing the risk of metastasis to other parts of the body. This suggests a more advanced stage of breast cancer and a poorer prognosis. The other characteristics listed may also be important factors in determining prognosis, but lymph node involvement is considered a stronger predictor.

The correct answer is "Release of virus from infected epithelial cells." This is because a neuraminidase inhibitor is a medication that specifically targets and inhibits the neuraminidase enzyme, which is responsible for the release of newly formed virus particles from infected cells. By inhibiting this process, the spread of the virus can be limited, leading to a decrease in the duration of the patient's symptoms.

The patient's symptoms of watery diarrhea, flushing, and dehydration, along with the low potassium concentration and high stool volume, are consistent with vasoactive intestinal polypeptide (VIP) secretion. VIP is a hormone that stimulates intestinal secretion and vasodilation, leading to increased fluid and electrolyte secretion in the intestines. This results in watery diarrhea and dehydration. Bacterial overgrowth, cholera, inactivation of lipase, and lactose intolerance do not typically cause such severe and prolonged watery diarrhea.

The most likely cause of the patient's pain is the accidental ligation of the ureter on the right. This is because the patient developed right flank pain after the surgery, and physical examination showed mild right flank tenderness. The ureter is a tube that carries urine from the kidneys to the bladder, and ligation of the ureter can cause obstruction and lead to pain in the affected area.

Tretinoin is a retinoid that works by activating nuclear gene transcription. It binds to retinoic acid receptors in the nucleus of cells, leading to increased gene expression. This increased gene expression promotes collagen synthesis, which can help improve the appearance of wrinkles in photodamaged skin. The other answer choices are not directly related to collagen synthesis.

The physician violated the principle of informed consent. Informed consent requires that the patient be provided with all relevant information about a medical procedure, including its benefits, risks, and alternatives, in order to make an informed decision. In this case, the physician only provided cursory information about the risks and follow-up of the pacemaker procedure, which does not meet the standard of informed consent.

The superior oblique muscle is most likely to remain intact in this patient. The patient's symptoms, including ptosis, lateral strabismus, and mydriasis, are consistent with damage to the oculomotor nerve (cranial nerve III). The oculomotor nerve innervates most of the extraocular muscles, including the superior rectus, inferior rectus, inferior oblique, and pupillary constrictor muscles. However, the superior oblique muscle is innervated by the trochlear nerve (cranial nerve IV), which is not affected in this patient. Therefore, the superior oblique muscle is the only muscle listed that would remain intact in this patient.

The correct answer is DNA gyrase. DNA gyrase is the target enzyme of ciprofloxacin, an antibiotic from the fluoroquinolone class. It is responsible for introducing negative supercoils into bacterial DNA, which is essential for DNA replication and transcription. Mutations in the genes encoding DNA gyrase can lead to resistance to ciprofloxacin, as the antibiotic is no longer able to bind and inhibit the enzyme effectively. This allows the bacteria, in this case Streptococcus pneumoniae, to survive and continue to cause infection despite treatment with ciprofloxacin.

Orlistat is the most likely cause of the steatorrhea and changes in lipid serum studies in this patient. Orlistat is a weight loss medication that works by inhibiting pancreatic lipase, the enzyme responsible for breaking down dietary fats. This leads to decreased absorption of fat in the intestines, resulting in oily, fatty bowel movements (steatorrhea). The weight loss and changes in lipid serum studies can be attributed to the decreased absorption of dietary fats.

The medical student's ability to effectively control his emotions by recognizing and dealing with his distress when working with patients with alcoholism suggests the mental mechanism of suppression. Suppression involves consciously pushing unwanted thoughts, feelings, or impulses out of awareness in order to cope with them. In this case, the student acknowledges his distress and actively learns methods to deal with it, indicating a conscious effort to suppress his negative emotions and work more effectively with these patients.

The correct answer is "Inhibition of renin release." In congestive heart failure, there is increased fluid volume and pressure in the atria. Atrial myocytes secrete atrial natriuretic peptide (ANP) in response to this increased pressure. ANP acts to counterbalance the effects of the renin-angiotensin-aldosterone system by inhibiting the release of renin from the kidneys. This leads to decreased levels of angiotensin II and aldosterone, which helps to reduce fluid retention and lower blood pressure.

Bupivacaine is a local anesthetic that works by blocking sodium channels in the cell membrane. By decreasing the permeability to sodium ions (Na+), bupivacaine prevents the generation and conduction of nerve impulses, leading to numbness and loss of sensation in the area where it is injected. This mechanism of action explains how bupivacaine can effectively block the transmission of pain signals in the median nerve, providing relief for carpal tunnel syndrome.

The presence of a disproportionate fear of serious disease is consistent with a diagnosis of hypochondriasis rather than undifferentiated somatoform disorder. Hypochondriasis is characterized by excessive worry and fear about having a serious medical condition, despite having little or no medical evidence to support the belief. This disproportionate fear is a key feature of hypochondriasis and distinguishes it from undifferentiated somatoform disorder, which is characterized by physical symptoms without a clear medical explanation. The other options, such as frequent health care visits, past history of unexplained symptoms, persistence of symptoms longer than 6 months, and presence of depressive symptoms, may be common in both hypochondriasis and undifferentiated somatoform disorder and do not specifically differentiate between the two.

This patient's disorder is most likely due to a defect in phagolysosome function. The clinical presentation of multiple bacterial infections since birth, along with neutropenia, suggests an immunodeficiency disorder. The presence of giant granules in the neutrophils indicates a defect in phagolysosome function, which is responsible for the intracellular killing of bacteria. This defect can lead to recurrent bacterial infections. Bone marrow suppression, defect in leukocyte adhesion, myeloperoxidase deficiency, and NADPH oxidase deficiency are not consistent with the clinical findings in this patient.

Based on the information provided, the most likely finding on neurologic examination of the patient prior to his death would be gait ataxia. This is because the patient had a long history of alcoholism, which can lead to damage to the cerebellum. Gait ataxia is a common manifestation of cerebellar dysfunction, causing unsteady and uncoordinated movements while walking. The other options, such as dysdiadochokinesia, dysmetria, essential tremor, and Romberg sign, are not specifically associated with alcoholism or pneumonia.

The probability of diarrhea having developed in people who consumed lettuce is 0.2. This is determined by taking the number of people who ate lettuce and became ill (40) and dividing it by the total number of people who ate lettuce (200).

The patient's condition is most likely caused by autosomal dominant inheritance because her brother, father, and paternal grandmother also had similar problems. Autosomal dominant inheritance means that only one copy of the mutated gene is needed to inherit the condition.

Loss of heterozygosity is the most likely explanation for the findings described. Loss of heterozygosity occurs when one allele is lost or inactivated in a tumor, resulting in the presence of only one allele. In this case, the analysis of the neoplastic cells shows the presence of only the m allele, indicating that the n allele has been lost. This loss of heterozygosity could be a result of a genetic event such as a deletion or mutation that specifically affects the n allele in the tumor cells.

The G-to-A transition in the mitochondrial DNA results in an added A:T base pair to the 3' end of the tRNA, which shortens the C loop. This mutation is most likely to affect mitochondrial function by causing decreased protein synthesis. tRNA molecules play a crucial role in protein synthesis by carrying amino acids to the ribosome. Any mutation in the tRNA can disrupt this process and lead to decreased protein synthesis. This can further contribute to the development of dilated cardiomyopathy, as proteins are essential for proper cardiac function.

During the experiment, epinephrine is injected, which is a hormone that activates B2-adrenoreceptors. B2-adrenoreceptors are known to cause relaxation of smooth muscles, including the muscles in the uterus. Therefore, the most likely physiologic effect observed in these animals would be uterine relaxation. This is because epinephrine would activate the B2-adrenoreceptors in the uterus, leading to relaxation of the uterine muscles.

An observational cohort study is the best description for this type of study because it involves following a group of individuals over a period of time (10 years in this case) and collecting data on their blood pressure, serum cholesterol concentration, smoking status, and deaths from coronary artery disease. This type of study allows researchers to observe the relationship between the risk factors (increased blood pressure) and the outcome (mortality from coronary artery disease) without intervening or manipulating any variables.

The most appropriate use of the deceased woman's money would be a program addressing cardiovascular disease. This is because cardiovascular disease is the leading cause of death in women, and the woman's philanthropic efforts were focused on addressing disparities in healthcare. By educating the public about cardiovascular disease, the program can help raise awareness, promote prevention, and improve access to healthcare for women, aligning with the woman's intentions and goals.

In the case of squamous cell carcinoma of the esophagus, surgical removal of the affected portion of the esophagus (esophagectomy) is often necessary. The arrows on the barium swallow indicate the region where the esophagectomy is most likely to be performed. Since the esophagus is located posterior to the trachea and anterior to the vertebral column, the region indicated by the arrows is in close proximity to the aorta. Therefore, ligation of arterial branches of the aorta would be involved in this procedure.

Nitric oxide is the most appropriate therapy for a newborn with persistent pulmonary hypertension. Nitric oxide is a selective pulmonary vasodilator that helps to relax the smooth muscles in the blood vessels of the lungs, improving oxygenation and reducing pulmonary hypertension. It is commonly used in neonatal intensive care units for this purpose. The other options, such as Desflurane, Hyperbaric oxygen, Nitrous oxide, and Oxygen diluted with helium, are not indicated for the treatment of persistent pulmonary hypertension in newborns.

The patient in the question has progressive clumsiness and fatigue, along with difficulty rising from a chair and unable to jump with both feet together. The physical examination shows hypertrophy of the calf muscles. These findings suggest a neuromuscular disorder, specifically weakness in hip adduction. The muscle responsible for hip adduction is the adductor magnus, which inserts onto the femur. The adductor magnus is innervated by the obturator nerve, which arises from the sacral plexus. The ischium is one of the bones that make up the pelvis, and the adductor magnus does not insert onto the ischium. Therefore, dysfunction of the muscle inserting onto the femur is most likely due to a problem with the anterior sacrum, not the ischium.