USMLE USMLE Certifications USMLE Questions & Answers

• Question 601:

  A 55-year-old hypertensive man develops sudden onset of excruciating pain beginning in the anterior chest, and then radiating to the back. Over the next 2 hours, the pain moves downward toward the abdomen. Which of the following is the most likely diagnosis?

  A. Aortic dissection

  B. Syphilitic aneurysm

  C. Aortic valve stenosis

  D. Atherosclerotic aneurysm

  E. Myocardial infarction

  Correct Answer: A

  Explanation:

  This patient has an aortic dissection (formerly called dissecting aneurysm), a potentially fatal condition that is too often confused clinically with myocardial infarction. The most important clinical clue is that the pain shifts with time. Noninvasive techniques, such as transesophageal echocardiography, CT, and MRI, are increasingly useful in making this diagnosis. Aortic valve stenosis would not be expected to produce severe chest pain of acute onset. This patient's clinical history does not suggest either an atherosclerotic or a syphilitic aneurysm. Even if he had one of either of these types of aneurysms and it had begun to rupture, the distinctive feature of severe pain moving downward would probably not be present. Myocardial infarction is the major diagnosis most often confused with this patient's condition. The movement of the pain is the major clinical tip-off suggesting that this is not the correct answer.

• Question 602:

  A 57-year-old woman with a history of hypertension and arthritis is referred to a rheumatologist for evaluation. A complete blood count (CBC) is normal, and a mini-chem panel shows no electrolyte abnormalities. Her erythrocyte sedimentation rate (ESR) is elevated, and an antinuclear antibody test (ANA) is positive. Further antibody studies are performed, and the results are shown below. Anti-histones high titer Anti-double stranded DNA not detected Anti-single stranded DNA not detected Anti-SSAnot detected Anti-SSB not detected Anti-SCI-70not detected Anti-Smith not detected Anti-centromere not detected Anti-RNP not detected. Which of the following diseases is suggested by these results?

  A. CREST syndrome

  B. Diffuse form of scleroderma

  C. Drug-induced lupus

  D. Sjögren syndrome

  E. Systemic lupus erythematosus (SLE)

  Correct Answer: C

  Explanation: The single finding of high autoantibody titers to histones, without any other autoantibodies, is characteristic of drug-induced lupus. The most commonly implicated drugs are procainamide, hydralazine (given for hypertension), and isoniazid. Patients typically have milder disease than in systemic lupus erythematosus (SLE) and tend to have arthritis, pleuropericardial involvement, and, less commonly, rash. CNS and renal disease are not usually observed. CREST syndrome is a milder variant of scleroderma characterized by calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly and telangiectasia. Anticentromere antibodies are diagnostic. The diffuse form of scleroderma, also known as systemic sclerosis, causes fibrosis of the skin and internal viscera. This disorder is characterized by anti-SCI-70 and often low titers of many other autoantibodies. Sjögren syndrome is characterized by dry eyes and dry mouth. Sjögren syndrome in isolation is characteristically positive for anti-SS-A and anti-SS-B. If it accompanies rheumatoid arthritis, anti-RNP will be positive as well. SLE is a multisystem disorder that is distinguished from drug-induced lupus by the presence of a wide variety of autoantibodies, including anti-double stranded DNA (Anti dsDNA).

• Question 603:

  A 67-year-old woman who has been in very good health is brought to her physician's office by her husband. He states that over the course of the past 5 years she has had difficulty recognizing her grandchildren, she has not been able to plan their daily activities, she has forgotten things left cooking on the stove, and at night she has been wandering through the house with an “absent” look on her face. She is beginning to demonstrate difficulty in recalling the names of common objects, and her speech is limited to simple two- or three-word sentences. Which of the following is the most likely diagnosis?

  A. Alzheimer disease

  B. Vascular dementia

  C. Amnestic disorder

  D. Pseudodementia

  E. Substance-induced persisting dementia

  Correct Answer: A

  Explanation:

  This woman has dementia of the Alzheimer type. A gradual onset of symptoms, general pervasive memory deficit, difficulties with language, and inability to plan, leading to severe impairment of daily functioning, are all characteristic of this dementia. Amnestic disorder is limited to memory problems, and this woman is demonstrating cognitive dysfunction, such as alterations in language and the loss of the ability to plan. Pseudodementia is incorrect since it is a major depressive disorder rather than a dementing condition. There is no evidence for a depressive syndrome in this patient's presentation. The diagnosis of substance-induced persisting dementia requires evidence of a history of substance abuse. However, it is the second most likely diagnosis and should be carefully explored with the husband and other close relatives and friends. Vascular dementia is generally characterized by a stepwise deterioration, not the gradual presentation of this case.

• Question 604:

  A premature infant develops progressive difficulty breathing over the first few days of life. Deficient surfactant synthesis by which of the following cell types may be contributing to the infant's respiratory problems?

  A. Alveolar capillary endothelial cells

  B. Bronchial mucous cells

  C. Bronchial respiratory epithelium

  D. Type I pneumocytes

  E. Type II pneumocytes

  Correct Answer: E

  Explanation:

  The child has neonatal respiratory distress syndrome (hyaline membrane disease). This condition is caused by the inability of the immature lungs to synthesize adequate amounts of surfactant. Surfactant, which reduces surface tension, helps keep alveoli dry, and aids in expansion of the lungs, is synthesized by type II pneumocytes. Alveolar capillary endothelial cells are important in maintaining the capillary structure and permitting flow of gases into and out of the bloodstream. Bronchial mucous cells produce the usually thin (in healthy individuals) coat of mucus that lines the bronchi. The ciliated bronchial respiratory epithelium is responsible for moving the dust-coated mucus layer out of the bronchi. Type I pneumocytes are the squamous cells that line alveoli and permit easy gas exchange. These cells tend to be immature (and thick) in premature infants but are not the producers of surfactant.

• Question 605:

  A 2-year-old boy has a CT scan of the head performed after a pediatrician notices a disproportionate growth in his head circumference compared with the rest of the body. The scan demonstrates a large choroid plexus papilloma involving the body of the right lateral ventricle. Which of the following brain structures might be affected by direct extension of this tumor?

  A. Caudate nucleus

  B. Pons

  C. Cerebellum

  D. Hippocampus

  E. Hypothalamus

  Correct Answer: A

  Explanation:

  Tumors of the ventricular system of the brain can affect the brain tissue either directly, via pressure on or invasion into a physically close structure, or indirectly, by obstructing CSF flow and causing hydrocephalus. Choroid plexus papillomas are highly differentiated, benign tumors that can involve any ventricle but have a predilection for involving the lateral ventricles of small children, particularly boys. The caudate nucleus is a C-shaped structure that comprises part of the wall of the lateral ventricle throughout its extent. The only structure listed that is adjacent to the body of the lateral ventricle, and would therefore be directly affected by the large tumor described in the question, is the caudate nucleus. The cerebellum overlies the fourth ventricle. The hippocampus is adjacent to the inferior (temporal) horn of the lateral ventricle. The hypothalamus abuts the third ventricle. The pons forms part of the floor of the fourth ventricle.

• Question 606:

  A patient consults a physician because of a small lesion on the lips that, on biopsy, proves to be a mucosal neuroma. The patient's mother had medullary carcinoma of the thyroid. In addition to medullary carcinoma of the thyroid, to which of the following conditions would this patient be particularly vulnerable?

  A. Gastrinoma

  B. Insulinoma

  C. Parathyroid adenoma

  D. Pheochromocytoma E. Pituitary adenoma

  Correct Answer: D

  Explanation:

  You should recognize this as a probable case of multiple endocrine neoplasia, specifically, MEN III (formerly MEN II b). Features of this autosomal dominant condition include medullary carcinoma of the thyroid, pheochromocytoma, and oral and intestinal ganglioneuromatosis (including mucosal neuromas). Gastrinomas, insulinomas, and pituitary adenomas are found in MEN I. Parathyroid adenomas are found in MEN I and II.

• Question 607:

  A man brings his 45-year-old wife to the emergency department. He states she has been ill for 3 days and has been running a temperature of 99.8 to 100.5 F. Today she is having difficulty staying awake, is talking to persons who are not there, and at times appears to be frightened of something. She is restless and somewhat combative when restrained. What is the most likely diagnosis?

  A. Acute stress disorder

  B. Bipolar I disorder, manic type

  C. Brief psychotic disorder

  D. Delirium

  E. Dementia

  Correct Answer: D

  Explanation:

  This is a psychotic level disorder (the patient is hallucinating). The patient has a fluctuating level of consciousness and is disoriented. Also, there is a clear history of a febrile condition that developed rather rapidly, all of which suggest delirium. In acute stress disorder a traumatic event occurs that precipitates an anxiety-type reaction, not a change in the sensorium. In both bipolar I disorder, manic type and brief psychotic disorder, patients may reach a level of behavioral disruption of psychotic proportion. They do not, however, demonstrate changes in level of consciousness or major disorientation. Persons with dementia demonstrate a clear sensorium with no fluctuations in the level of consciousness. In addition, persons with dementia predominantly show symptoms of impairment of cognitive functions (e.g., memory impairment).

• Question 608:

  A patient presents to a physician with jaundice. Physical examination reveals a nodular, enlarged liver. CT of the abdomen shows a cirrhotic liver with a large mass. CT-guided biopsy of the mass demonstrates a malignant tumor derived from hepatic parenchymal cells. Infection with which of the following viruses would most likely be directly related to the development of this tumor?

  A. Epstein-Barr virus (EBV)

  B. Hepatitis B virus (HBV)

  C. Human herpesvirus type 8 (HHV 8)

  D. Human papillomavirus (HPV)

  E. Human T-lymphocyte virus (HTLV-1)

  Correct Answer: B

  Explanation:

  The tumor is hepatocellular carcinoma, which usually develops in the setting of cirrhosis owing to a variety of damaging agents, including hepatitis B virus (HBV) infection, alcohol use, and hemachromatosis. Epstein-Barr virus (EBV) is associated with Burkitt lymphoma and nasopharyngeal carcinoma. Human herpesvirus type 8 (HHV 8), a member of the herpes family, is associated with Kaposi sarcoma. Human papillomavirus (HPV) is associated with cervical, penile, and anal carcinoma. Human T-lymphocyte virus (HTLV-1) is associated with adult T-cell leukemia.

• Question 609:

  A new antifungal medication is being tested in Phase I clinical trials. Examination of the pharmacokinetic

  properties of the drug reveals that the half-life of the drug is 6 hours.

  If a continuous intravenous infusion of this drug were started on a research subject, how long

  would it take to reach 75% of steady state?

  A. 3 hours

  B. 6 hours

  C. 9 hours

  D. 12 hours

  E. 18 hours

  F. 24 hours

  Correct Answer: D

  Explanation:

  The rule of thumb is that the plasma concentration will reach 50% in one half-life, 75% in two half-lives, 87.5% in three half-lives, etc., so that the difference between the current drug level and 100% halves with each half-life. In this instance, it takes two half-lives to reach 75%. The half-live of this drug is 6 hours, so two half-lives is 12 hours.

• Question 610:

  A 5-year-old girl is thoroughly evaluated because of growth failure. The child has been complaining of headaches, which are exacerbated when she tries to read. Funduscopic examination reveals papilledema. CT scan demonstrates a mass involving the area above and within the sella turcica. Surgical resection of the mass yields a multiloculated cystic and solid tumor containing dark brown, oily fluid. This tumor is thought to arise from epithelial rests derived from which of the following structures?

  A. Hypothalamus

  B. Pineal gland

  C. Posterior pituitary gland

  D. Rathke's pouch

  E. Superior colliculus

  Correct Answer: D

  Explanation:

  The tumor described is a craniopharyngioma, which is one of the more common brain tumors of children. These tumors arise from epithelial rests derived from Rathke's pouch, which is an oral invagination that gives rise to the cells that form the anterior pituitary gland. Histologically, craniopharyngiomas can resemble ameloblastomas, which are tumors derived from dental epithelium. Note that this question could also have been answered very simply by noting that the hypothalamus, pineal gland, pituitary gland, and the superior colliculus are all adult structures; only Rathke's pouch is an embryonic structure. Therefore, only Rathke's pouch could be the source of epithelial rests, which are remnants of embryonic tissues that persist in the adult. Although craniopharyngiomas often occur near the hypothalamus and posterior portion of the pituitary gland, they do not arise from neural tissue. The pineal gland and superior colliculus are found on the posterior aspect of the brain stem.