USMLE USMLE Certifications USMLE Questions & Answers

• Question 421:

  A 6-year-old male is brought to the physician due to a sore throat, fever and malaise. Physical examination reveals an erythematous tongue and a sandpaper-like body rash. This most likely sequelae of this infection includes all of these except

  A. hematuria

  B. joint pain

  C. muscular spasm

  D. myocarditis

  E. nodules under the skin

  Correct Answer: C

  Explanation:

  Group A Streptococcus pyogenes is a bacitracin sensitive beta-hemolytic gram-positive bacterium which can cause pyogenic, toxigenic and immunologic illnesses. This patient most likely has scarlet fever which presents with streptococcal pharyngitis, circumoral pallor and a sandpaper-like body rash. Streptococcal infections can be complicated with rheumatic fever or post streptococcal glomerulonephritis. Laboratory findings include the presence of anti-DNase B antibodies and elevated anti-streptolysin (ASO) titers. Antibodies to the M protein enhance host defenses but can also cause rheumatic fever due to molecular mimicry. Prophylaxis with penicillin is indicated to prevent rheumatic fever. Rheumatic fever is characterized by myocarditis, migratory polyarthritis, erythema marginatum, Sydenham chorea and subcutaneous nodules. Acute post streptococcal glomerulonephritis presents with hematuria, periorbital edema and hypertension. Muscular spasms are not features of rheumatic fever or post streptococcal glomerulonephritis.

• Question 422:

  A 50-year-old male who is a known alcoholic is brought to the emergency department by police. He complains of a productive cough with thick, bloody sputum. Vitals reveal a temperature of 38°C (100.4 °F). Physical examination reveals dullness to percussion, increased tactile fremitus and decreased breath sounds over the right lung fields. A chest radiograph is obtained which reveals consolidation in the right upper lobe. The most likely cause of these findings is a

  A. gram-negative oxidase-negative bacillus

  B. gram-positive oxidase-positive bacillus

  C. gram-negative pleomorphic bacillus

  D. gram-positive catalase-negative coccus

  E. gram-positive catalase-positive coccus

  Correct Answer: A

  Explanation:

  This patient who is an alcoholic with a productive cough with “currant jelly sputum” and lobar consolidation most likely has pneumonia caused by Klebsiella pneumoniae. Klebsiella pneumoniae is a gram-negative, oxidase-negative rod which is part of the intestinal flora. It produces mucoid colonies due to polysaccharide capsules and causes aspiration pneumonia in diabetics and alcoholics. It is also associated with multidrug resistance. Treatment is with a third-generation cephalosporin with or without an aminoglycoside.

• Question 423:

  A 65-year-old female with end stage renal failure comes to her physician with a rash and is diagnosed with Lyme disease. Review of her medical records reveals severe allergic reactions to penicillin and macrolides. The most appropriate treatment for this patient's current disease is

  A. demeclocycline

  B. doxycycline

  C. metronidazole

  D. oxytetracycline

  E. tetracycline

  Correct Answer: B

  Explanation:

  Tetracyclines such as doxycycline are antibiotics commonly used to treat infections such as Rocky Mountain spotted fever, typhus and Lyme disease, which are all caused by spirochetes. They are also used for the treatment of acne, sexually transmitted diseases and for susceptible organisms in patients who are allergic to penicillin. The treatments for Lyme disease without neurologic symptoms or heart block include doxycycline and amoxicillin. Doxycycline and minocycline are tetracyclines excreted largely by routes other than the kidneys. They are secreted in an inactive form into the intestinal lumen and eliminated in the feces. The other tetracyclines listed are concentrated by the liver in the bile and excreted in the urine and feces unchanged hence, they are not the best treatment option in this patient with renal failure. Metronidazole is not used to treat Lyme disease.

• Question 424:

  A 25-day-old male is brought to the physician due to seizures, rigidity and frequent viral infections. Physical examination reveals a neonate with cyanosis in the lower extremities. The most likely cause of these findings is a

  A. defect in the IL-2R gamma chain

  B. defect in the lysosomal trafficking regulation gene

  C. defect in the tyrosinase kinase gene

  D. deletion in chromosome 22q11.2

  E. mutation in the STAT3 gene

  Correct Answer: D

  Explanation: The patient most likely has thymic aplasia which is also known as DiGeorge syndrome. It is caused by a deletion in chromosome 22q11.2 which leads to failure of the third and fourth pharyngeal pouches to develop. The features of DiGeorge syndrome include conotruncal cardiac anomalies such as tetralogy of Fallot and truncus arteriosus, an absent thymus gland which leads to T-cell deficiency and frequent viral infections, and hypocalcemia due to a hypoplastic parathyroid. The congenital heart defect may lead to cyanosis and the hypocalcemia can present with seizures and tetany. Laboratory findings include decreased T cell levels, decreased parathyroid hormone, decreased calcium levels and a thymic shadow on a chest x-ray.

• Question 425:

  A 35-year-old male comes to the physician due to watery diarrhea of two weeks’ duration. He also has a low-grade fever, fatigue and weight loss of 5kg (11 lbs) over the past month. Laboratory findings include a CD4+ T cell count 70 cells/mm³. To find the cause of his diarrhea, the next best step is a test involving

  A. acid fast staining of the stool

  B. cysts with multiple nuclei in the stool

  C. peripheral blood smears

  D. silver staining of the stool

  E. toxins in the stool

  Correct Answer: A

  Explanation:

  Cryptosporidium is a protozoa commonly associated with chronic watery diarrhea in HIV/AIDS patients with CD4+ cell counts less than < 100 cells/mm³.It causes milder diarrhea in immunocompetent hosts and can be treated with nitazoxanide and prevented by filtering the city water supplies. The diagnosis can be made by acid fast staining of a stool specimen which reveals the presence of acid-fast oocysts.

• Question 426:

  A 12-year-old female is brought to the physician by her mother due to a severe sore throat. She has significant pain with swallowing and generally feels tired. Her mother also reports that the patient has had a high fever for the past four days. Physical examination reveals an erythematous patch on the upper posterior pharynx and tenderness of the cervical lymph nodes. Vitals reveal a temperature of 39.5°C (103.1°F). The nerve responsible for this patient's throat pain is also involved in

  A. head rotation to opposite side

  B. movement of intrinsic tongue muscles

  C. sensation of the lower jaw

  D. sensory input from carotid sinus baroreceptors

  E. taste in the anterior two thirds of the tongue

  Correct Answer: D

  Explanation:

  Afferent nerve fibers (sensory) travel to the central nervous system (CNS) while efferent nerve fibers (motor) travel away from the CNS. The glossopharyngeal nerve (cranial nerve IX) carries general somatic sensation from the posterior part of the upper pharynx, eustachian tube, middle ear and posterior one third of the tongue. It also conveys afferent fibers from the carotid sinus baroreceptors, carotid body chemoreceptors and taste sensation from the posterior one third of the tongue as well as parasympathetic efferents to the parotid gland via the otic ganglion. Difficulty swallowing (dysphagia) and painful swallowing (odynophagia) can result from a variety of causes including abnormal motor innervation to the muscles of the pharynx or esophagus (vagus nerve), disorders of esophageal motility and of the lower esophageal sphincter (achalasia) and compression of the pharynx or esophagus from nearby structures such as in left atrial enlargement.

• Question 427:

  A 55-year-old female comes to the physician with a dry cough of three weeks’ duration. The cough is not associated with sputum or blood production and she is afebrile. She has a medical history of rheumatoid arthritis, peptic ulcer disease and hypertension for which is receiving treatment. The most likely cause of her chief complaint is:

  A. aspirin

  B. hydrochlorothiazide

  C. infliximab

  D. lisinopril

  E. metronidazole

  Correct Answer: D

  Explanation:

  ACE inhibitors such as lisinopril block the conversion of angiotensin I to angiotensin II which leads to decreased arteriolar resistance, decreased aldosterone levels, decreased glomerular filtration rates and increased renin levels. They are used to treat hypertension, diabetic nephropathy and heart failure. Inhibition of the angiotensin converting enzyme (ACE) also prevents inactivation of bradykinin which can cause a persistent dry cough and angioedema due to elevated bradykinin levels. Other side effects of ACE inhibitors include teratogenesis, increased creatinine, hyperkalemia and hypotension. They are contraindicated in patients with bilateral renal stenosis and C1 esterase inhibitor deficiency. This patient who has developed a cough due to lisinopril use should be switched to an angiotensin II receptor blocker such as losartan.

• Question 428:

  A 30-year-old female is brought to the emergency department after being involved in a motor vehicle accident. She was not wearing a seatbelt and was ejected from her car seat upon collision with a tree. Physical examination reveals several lacerations on her face and chest as well as an inability to open her mouth against resistance. The muscle which was most likely injured is the

  A. lateral pterygoid muscle

  B. masseter muscle

  C. medial pterygoid muscle

  D. orbicularis oris muscle

  E. temporalis muscle

  Correct Answer: A

  Explanation:

  The lateral pterygoid muscles consist of two heads: an upper head arising from the infratemporal surface of the greater wing of the sphenoid bone and a lower head arising from the lateral pterygoid plate. The lateral pterygoids act to pull the mandible forward in the process of opening the jaw against resistance. Its other actions include protracting the mandible and moving it from side to side while chewing food.

• Question 429:

  A 30-year-old Caucasian male with HIV/AIDS develops right-sided weakness involving his right leg. A MRI of his brain reveals multiple ring enhancing lesions within the white matter in his left frontal lobe. The most likely source of this infection in the United States is

  A. Anopheles mosquito bite

  B. bird droppings

  C. cooling systems

  D. poorly cooked pork

  E. rodent droppings

  Correct Answer: D

  Explanation:

  This patient has AIDS which predisposes him to opportunistic infections such as toxoplasmosis. The classic presentation of the reactivation of toxoplasmosis in AIDS patients is the presence of brain abscesses which are seen as multiple ring enhancing lesions on a MRI. Toxoplasma gondii is a protozoan which infects humans who ingest the oocysts from cat feces or improperly cook lamb or pork. Although cats are the necessary definitive host, the most common source of infection in the United States is poorly cooked pork. Immunocompromised hosts and fetuses are vulnerable to severe infection. In the fetus, toxoplasmosis causes extensive damage to the brain parenchyma and retina. Treatment is with sulfadiazine and pyrimethamine. In AIDS patients, the most frequent causes of ring enhancing lesions are primary brain lymphoma and toxoplasmosis.

• Question 430:

  A 50-year-old male with AIDS develops a fever, headache and stiff neck. A sample of his cerebrospinal fluid reveals the presence of lymphocytes, glucose levels of 35 mg/dL and protein levels of 75 mg/dL. The test which would most likely confirm this patient's diagnosis is the:

  A. India ink test

  B. latex particle agglutination test

  C. molecular probe test

  D. polymerase chain reaction test

  E. Tzanck smear

  Correct Answer: B

  Explanation:

  This patient with AIDS most likely has meningitis caused by Cryptococcus neoformans, which is a heavily encapsulated yeast found in pigeon droppings and acquired through inhalation. The fungi can be highlighted with India ink and mucicarmine but latex particle agglutination testing is more specific. It detects the polysaccharide capsular antigens shed into the CSF. Cryptococcal meningitis is an opportunistic infection and treatment is with amphotericin B and flucytosine followed by fluconazole.