USMLE USMLE Certifications USMLE Questions & Answers

• Question 591:

  In a hospital cardiac care unit, there are three patients with different cardiac conditions: a 52-year-old man with dilated cardiomyopathy, an 18-year-old girl with mitral valve prolapse, and a 30-year-old man with infective endocarditis of the mitral valve. Which of the following features do all these patients most likely share?

  A. Decreased compliance

  B. Depressed myocardial contractility

  C. Infectious etiology

  D. Mitral valve stenosis

  E. Risk of systemic thromboembolism

  Correct Answer: E

  Explanation:

  Systemic thromboembolism may develop in each of these patients. Vegetations associated with infective endocarditis may undergo fragmentation and result in systemic thromboembolism. Stasis develops in dilated ventricles, which predisposes to formation of thrombi attached to the ventricular walls (mural thrombi). Mural thrombi may also form within the left atrium in the presence of mitral valve prolapse. Thromboemboli may originate from mural thrombi. Decreased compliance is a pathophysiologic alteration present in a variety of cardiac disorders in which there is impediment to expansion or relaxation of ventricular walls, such as restrictive cardiomyopathy, hypertrophic cardiomyopathy, and constrictive pericarditis. This feature is not present in any of the conditions described in the question. Depressed myocardial contractility results from conditions that impair myocardial inotropism, such as dilated cardiomyopathy and ischemic heart disease. Depressed inotropism is not present in infective endocarditis or mitral valve prolapse. Of the three conditions in the question stem, only infective endocarditis is definitely related to an infectious etiology, usually bacteria. Recall that mitral valve prolapse is due to myxomatous degeneration of the mitral valve, sometimes associated with Marfan syndrome. The etiology of dilated cardiomyopathy is heterogeneous, and most cases are idiopathic. Of the remaining cases, viral infections, toxic insults (especially alcohol), metabolic disorders (hemochromatosis), pregnancy, and genetic influences are the underlying causes. Mitral valve stenosis may develop as a result of vegetations forming on the mitral valve and occluding the valvular orifice. Endocarditis of the mitral valve more often leads to mitral insufficiency because of destruction of valve leaflets or rupture of chordae tendineae. On the contrary, both mitral valve prolapse (usually clinically silent) and dilated cardiomyopathy may lead to mitral valve insufficiency and regurgitation.

• Question 592:

  The table below depicts blood pressure values taken from six adults. Which set of values is most consistent with aortic regurgitation?

  Systolic pressure (mmHg) Diastolic pressure (mmHg)

  1.

  50 Undetectable

  2.

  9580

  3.

  12080

  4.

  16050

  5.

  170100

  6.

  220130

  A. 1

  B. 2

  C. 3

  D. 4

  E. 5

  Correct Answer: D

  Explanation:

  A patient with aortic regurgitation, caused by insufficiency of the aortic valve, has a wide pulse pressure (the difference between systolic and diastolic pressure). In fact, during diastole, the systemic pressure precipitously drops as the blood flows from the aorta back into the left ventricle through the incompetent aortic valve. Systolic pressure remains relatively normal since it depends on the left ventricular ejection.

  Aortic stenosis is associated with reduced systolic pressure and relatively preserved diastolic pressure, such as 95/80 mmHg, since the left ventricle is unable to pump a normal amount of blood through a stenotic valvular orifice. A blood pressure of 50/undetectable mmHg is characteristic of acute shock. A blood pressure of 120/80 mmHg is considered within normal limits in healthy adults, whereas 160/95 mmHg is definitely in the range of hypertension, although mild. A blood pressure of 220/130 mmHg is typical of malignant hypertension, a severe condition that may lead to life-threatening complications if not promptly treated.

• Question 593:

  A 61-year-old man presents with a chief complaint of difficulty swallowing. To evaluate his dysphagia, the physician orders a barium swallow with fluoroscopy, as well as an esophagogram. She finds that the anterior wall of the esophagus in the mid-thorax is being compressed. Which of the following structures is most likely responsible for this compression?

  A. Left atrium

  B. Right ventricle

  C. Left ventricle

  D. Pulmonary trunk

  E. Right atrium

  Correct Answer: A

  Explanation:

  The left atrium forms most of the posterior wall of the heart. The esophagus passes immediately posterior to the heart. Enlargement of the left atrium may compress the esophagus and cause dysphagia. The left ventricle forms most of the left border of the heart and most of the diaphragmatic surface of the heart. The left ventricle is not related to the esophagus. The pulmonary trunk emerges from the right ventricle on the anterior surface of the heart. The pulmonary trunk is not related to the esophagus. The right atrium forms the right border of the heart. It is not related to the esophagus. The right ventricle forms most of the anterior wall of the heart and a small portion of the diaphragmatic surface of the heart. It is not related to the esophagus.

• Question 594:

  During a fight, a 32-year-old man is hit on the back of the neck with a chair. A CT scan reveals a bony fragment that penetrated the lateral portion of the dorsal columns. Which of the following functions would most likely be affected by a lesion at this site?

  A. Fine motor control of the ipsilateral fingers

  B. Motor control of the contralateral foot

  C. Proprioception from the ipsilateral leg

  D. Sweating of the ipsilateral face

  E. Vibratory sense from the ipsilateral arm

  Correct Answer: E

  Explanation:

  At this level, the lateral portion of the dorsal columns (funiculus) is composed of the fasciculus cuneatus. Axons carrying tactile, proprioceptive, and vibratory information from the ipsilateral arm enter the spinal cord via the dorsal root, ascend the cord in the fasciculus cuneatus, and synapse in the nucleus cuneatus of the caudal medulla. Secondary neurons from this nucleus give rise to internal arcuate fibers, which decussate and ascend to the thalamus (ventral posterolateral nucleus, VPL) as the medial lemniscus. Tertiary neurons from the VPL project to the ipsilateral somatosensory cortex. Therefore, damage to the fasciculus cuneatus would result in a deficit in tactile, proprioceptive, and vibratory sense in the ipsilateral arm, because the fibers that carry this information do not cross until they reach the medulla. Fine motor control of the fingers would be carried principally by the ipsilateral lateral corticospinal tract in the lateral funiculus of the cord. Motor control of the contralateral foot is carried by the ipsilateral corticospinal tract in the lateral funiculus of the cord. Proprioception from the ipsilateral leg is carried by the fasciculus gracilis in the medial part of the dorsal columns. Hemianhidrosis (lack of sweating) of the face could be produced by interruption of sympathetic innervation to the face. The hypothalamospinal tract projects from the hypothalamus to the intermediolateral cell column at levels T-1 to T-2. It descends the cord in the lateral funiculus of the cord. Interruption of this tract results in Horner syndrome (miosis, ptosis, hemianhidrosis).

• Question 595:

  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 practitioner should also look for signs of:

  A. cystinuria

  B. hypoglycemia

  C. iron deficiency anemia

  D. sphingomyelin accumulation

  E. vitamin A deficiency

  Correct Answer: E

  Explanation:

  The child likely has cystic fibrosis. In this disorder, an abnormality of chloride channels causes all exocrine secretions to be 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 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 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 is not typically found in children with cystic fibrosis. Sphingomyelin accumulation is generally associated with deficiency of sphingomyelinase, as seen in Niemann-Pick disease.

• Question 596:

  A 44-year-old businessman presents to a physician because of a markedly inflamed and painful right great toe. He states that he just returned from a convention, and noticed increasing pain in his right foot during his plane trip home. Physical examination is remarkable for swelling and erythema of the right great toe as well as small nodules on the patient's external ear. Aspiration of the metatarsal-phalangeal joint of the affected toe demonstrates needle-shaped negatively birefringent crystals. Which of the following agents would provide the most immediate relief for this patient?

  A. Allopurinol

  B. Aspirin

  C. Colchicine

  D. Probenecid

  E. Sulfinpyrazone

  Correct Answer: C

  Explanation:

  The patient has gout, which is due to precipitation of monosodium urate crystals in joint spaces (notably the great toe) and soft tissues (causing tophi, which are often found on the external ears). Colchicine reduces the inflammation caused by the urate crystals by inhibiting leukocyte migration and phagocytosis secondary to an effect on microtubule assembly. Allopurinol and its metabolite, oxipurinol, inhibit xanthine oxidase, the enzyme that forms uric acid from hypoxanthine. Therapy with this agent should be begun 1-2 weeks after the acute attack has subsided. Aspirin competes with uric acid for tubular secretion, thereby decreasing urinary urate excretion and raising serum uric acid levels. At high doses (more than 2 gm daily) aspirin is a uricosuric. Probenecid and sulfinpyrazone are uricosuric agents, increasing the urinary excretion of uric acid, hence decreasing serum levels of the substance. Therapy with these agents should be begun 1-2 weeks after the acute attack has subsided.

• Question 597:

  An oncologist tells his patient that her laboratory results support a diagnosis of advanced malignant melanoma with multiple metastases to the liver and brain. He also advises her that the prognosis is poor. Which of the following is most likely to be the first statement that the patient will make?

  A. "Can you keep me alive until my daughter graduates from medical school?"

  B. "Damn you doctor, you should have caught this earlier!"

  C. "Doctor, you must be wrong."

  D. "I think it is time that I make a will and say good-bye to everyone."

  E. "It's no use, I always lose and get the short end of the stick."

  Correct Answer: C

  Explanation:

  Kubler-Ross's Death and Dying sequence is a stepwise process with five identified stages, which occur in the following order: 1) Denial, 2) Anger, 3) Bargaining, 4) Sadness, and 5) Acceptance. "Doctor you must be wrong" is the correct answer since it reflects the patient's inability to accept the information and indicates the denial of the first stage. "Can you keep me alive until my daughter graduates from medical school", is a statement from the third, or bargaining, stage. "Damn you doctor, you should have caught this earlier" is a statement from the second, or anger, phase. "I think it is time that I make a will and say goodbye to everyone" reflects the patient's acceptance of the reality and is a statement from the fifth phase (acceptance). "It's no use, I always lose and get the short end of the stick" is a statement from the fourth phase (sadness).

• Question 598:

  A 67-year-old man is evaluated for persistent shooting pains, lower limb ataxia, and bladder dysfunction. Physical examination demonstrates small irregular pupils that constrict with accommodation but not in response to light. A VDRL test is positive. A CT scan of the spinal cord would most likely demonstrate atrophy of which of the following structures?

  A. Dorsal column

  B. Ventral horn

  C. Dorsal horn

  D. Lateral column

  E. Ventral column

  Correct Answer: A

  Explanation: The patient has tabes dorsalis, which is a form of neurosyphilis seen 10 to 25 years or longer after primary disease. The pupils described are Argyll Robertson pupils and are considered diagnostic for neurosyphilis. Characteristically, the dorsal columns, which contain the ascending tracts for sensory information, become atrophic, probably as a result of damage to the dorsal root ganglion cells. The dorsal gray horn contains neurons that respond to sensory input. The lateral column contains both descending (e.g., lateral corticospinal, rubrospinal tracts) and ascending (e.g., spinocerebellar tracts, spinothalamic tracts) tracts. The ventral column contains both descending (e.g., anterior corticospinal, tectospinal) and ascending (e.g., spinothalamic) tracts. The ventral horn contains lower motor neurons.

• Question 599:

  A 54-year-old African-American woman undergoes a routine insurance physical examination. Chest x-ray film reveals bilateral hilar masses. Biopsy of the masses shows granulomata, but acid-fast and fungal stains are negative for organisms. Which of the following is the most likely diagnosis?

  A. Caroli disease

  B. Raynaud disease

  C. Sarcoidosis

  D. Scleroderma

  E. Systemic lupus erythematosus

  Correct Answer: C

  Explanation:

  Sarcoidosis is a multisystem disease characterized by noncaseating granulomata in a variety of organs. The disease may be symptomatic (respiratory and constitutional symptoms) or may be discovered incidentally when chest x-ray or autopsy reveals bilateral hilar adenopathy. Definitive diagnosis is based on biopsy, which reveals noncaseating granulomata that are negative for fungi or acid-fast bacilli. Sarcoidosis is more common in individuals of African-American descent. Caroli disease is a congenital malformation of the bile duct system. Raynaud disease is a vasospasm of vessels that causes temporary ischemia in the hands. Scleroderma, or progressive systemic sclerosis, is characterized by progressive fibrosis of skin and internal organs. Systemic lupus erythematosus is an autoimmune disease characterized by vasculitis (which may produce a variety of symptoms depending on the site of the lesion), rash, renal disease, hemolytic anemia, and neurologic disturbances.

• Question 600:

  A 22-year-old woman presents to her physician with amenorrhea, weight loss, anxiety, tremor, heat intolerance, and palpitations. Laboratory examination is consistent with hyperthyroidism, and the physician prescribes propylthiouracil. The patient's response to propylthiouracil is disappointing, and the symptoms recur, then worsen. Subtotal thyroidectomy is successfully performed, but following the surgery, the woman is extremely hoarse, and can barely speak above a whisper. This hoarseness is most probably related to damage to a branch which of the following cranial nerves?

  A. Facial

  B. Glossopharyngeal

  C. Hypoglossal

  D. Trigeminal

  E. Vagus

  Correct Answer: E

  Explanation: The recurrent laryngeal nerves are branches of the vagus (CN X) and supply all intrinsic muscles of the larynx except the cricothyroid. The right recurrent laryngeal nerve recurs around the right subclavian artery. The left recurrent laryngeal nerve recurs in the thorax around the arch of the aorta and ligamentum arteriosum. Both nerves ascend to the larynx by passing between the trachea and esophagus, near the thyroid gland. The recurrent laryngeal nerves are therefore particularly vulnerable during thyroid surgery, and damage may cause extreme hoarseness. The facial nerve innervates the muscles of facial expression, the stapedius muscle, and the lacrimal, submandibular and sublingual glands. It also mediates taste sensation from the anterior two thirds of the tongue. The glossopharyngeal nerve innervates the stylopharyngeus muscle and the parotid gland. Visceral afferents supply the carotid sinus baroreceptors and carotid body chemoreceptors, and mediate taste from the posterior one third of the tongue. Somatosensory fibers supply pain, temperature, and touch information from the posterior one third of the tongue, upper pharynx, middle ear, and eustachian tube. The hypoglossal nerve innervates the intrinsic muscles of the tongue, the genioglossus, hypoglossus, and styloglossus muscles. The trigeminal nerve receives sensory information from the face and innervates the muscles of mastication.