USMLE USMLE Certifications USMLE Questions & Answers

• Question 461:

  A 15-year-old female is brought to the physician by her mother because she is concerned that she has not started menstruating. Physical examination reveals the patient's vagina is very shallow without a palpable uterus. There are also palpable masses in the labia majora. Karyotype analysis reveals a 46, XY genotype. Which of the following was most likely present during the early fetal life of this patient?

  A. A uterus

  B. An oviduct

  C. Decreased androgen levels

  D. Mullerian inhibiting factor

  E. Streak ovaries

  Correct Answer: D

  Explanation:

  Androgen insensitivity syndrome also known as testicular feminization is a disorder of sexual development characterized by uterovaginal agenesis. Patients appear phenotypically female and may have breasts but lack a uterus and other female internal reproductive organs. They also have XY chromosomes and are genotypically males. The gene for testes-determining factor (TDF) is on the Y chromosome and it causes the indifferent gonads to develop into testis-containing Sertoli cells. Sertoli cells secrete Mullerian inhibitory factor (MIF), a substance that suppresses the development of paramesonephric ducts, preventing the formation of female internal reproductive organs.

• Question 462:

  A 5-month-old male is brought to the physician by his parents due to twitching of his facial muscles. Review of his medical records reveals that he has previously been treated for several episodes of Candida infections. Physical examination reveals low set ears, hypertelorism and a shortened philtrum. The most likely additional finding in this patient is

  A. absence of type IV hypersensitivity

  B. decreased alpha fetoprotein

  C. elevated IgE levels

  D. elevated IgM levels

  E. prominent telangiectasias around the eyes

  Correct Answer: A

  Explanation:

  This patient most likely has thymic aplasia which is also known as DiGeorge syndrome. It is caused by a 22q11 deletion and failure of the 3rd and 4th pharyngeal pouches to develop which leads to the absence of the thymus and parathyroid glands. Patients may present with tetany, usually seen in the facial muscles, due to hypocalcemia secondary to hypoparathyroidism. Recurrent infections due to defective cellular immunity and abnormal facies are due to decreased levels of T cells since patients without a thymus are unable to complete normal T-lymphocyte development. Type IV hypersensitivity which is totally dependent on T lymphocytes is absent in these patients. Other findings include tetralogy of Fallot and truncus arteriosus.

• Question 463:

  A 34-year-old female comes to the physician with nausea and abdominal pain. She indicates that the pain is epigastric and it improves with food intake. She also reports recent weight gain. A urease breath test is obtained which is positive. The most likely cause of these findings has all the following characteristics except

  A. catalase positivity

  B. gram negativity

  C. gram positivity

  D. oxidase positivity

  E. urease positivity

  Correct Answer: C

  Explanation:

  This patient most likely has a duodenal ulcer caused by infection with Helicobacter pylori. Duodenal ulcers present with epigastric pain which improves with eating hence patients tend to gain weight. Helicobacter pylori is a urease positive, catalase positive, oxidase positive, curved shaped gram-negative bacterium. The urease it possesses produces ammonia which creates an alkaline environment that promotes the survival of the bacteria in acidic mucosa. It may colonize the antrum of the stomach and cause gastric ulcers or colonize the first part of the duodenum causing duodenal ulcers. Infection with H. pylori increases the risk for gastric adenocarcinomas and MALT lymphomas. The diagnosis can be made with a positive urea breath test or fecal antigen test. Treatment regimens include triply therapy with amoxicillin, clarithromycin and omeprazole or alternatively quadruple therapy with bismuth subsalicylate, metronidazole, tetracycline and omeprazole.

• Question 464:

  A 24-year-old female comes to the physician due to urinary frequency and burning with urination. She is diagnosed with a urinary tract infection and prescribed ciprofloxacin. The mechanism of action of ciprofloxacin is by

  A. creation of transmembrane channels

  B. inhibition of cell wall synthesis

  C. inhibition of dihydrofolate reductase

  D. inhibition of DNA gyrase

  E. inhibition of protein synthesis

  Correct Answer: D

  Explanation:

  Fluoroquinolones are a class of antibiotics which work by inhibiting topoisomerase II also called DNA gyrase and IV in prokaryotes. These drugs include ciprofloxacin, ofloxacin, gemifloxacin and enoxacin. They should not be taken together with antacids. They are used in the treatment of urinary and GI tract infections with gram-negative bacteria. They are contraindicated in pregnant women, nursing mothers and children < 18 years old due to possible cartilage damage. Other side effects of fluoroquinolones include QT interval prolongation, tendon rupture in patients over 60 years old, skin rashes, dizziness and inhibition of cytochrome P-450 enzymes.

• Question 465:

  A 2-hour-old female who is born at 37 weeks' gestation has purple patches on her skin as well as hepatosplenomegaly and jaundice. A CT of the head is obtained which reveals periventricular calcifications. The most likely cause of these findings is also responsible for:

  A. hairy oral leukoplakia

  B. heterophile negative mononucleosis

  C. Hodgkin lymphoma

  D. Kaposi sarcoma

  Correct Answer: B

• Question 466:

  A 53-year-old man comes to the physician because of a 6-month history of intermittent blood in his stool. He has had no pain with defecation. Physical examination shows a 1-cm, visible anal mass located below the dentate line. A biopsy of the mass is scheduled. If the mass if found to be malignant, it is most appropriate to evaluate which of the following lymph nodes for possible metastasis?

  A. Internal iliac

  B. Popliteal

  C. Sacral

  D. Superficial inguinal

  E. Superior rectal

  Correct Answer: D

• Question 467:

  A 59-year-old man is brought to the emergency department because of a 4-day history of nausea, vomiting, and diarrhea. He also has been confused and agitated during this period. He has a history of mild hypertension. His current medication is a diuretic. His temperature is 37°C (98.6°F), pulse is 108/min, respirations are 26/min, and blood pressure is 70/47 mmHg. Physical examination shows delayed capillary refill of the lips and nail beds and cool extremities. His oxyhemoglobin saturation in a central vein is 60% (N = 70 - 75). These findings are most consistent with which of the following types of shock?

  A. Cardiogenic

  B. Distributive

  C. Hypovolemic

  D. Obstructive

  E. Septic

  Correct Answer: C

• Question 468:

  A 31-year-old woman comes to the physician because of a 2-week history of malaise, nausea, vomiting, and decreased appetite. She is a known user of intravenous heroin. She appears chronically ill. She is 165 cm (5 ft 5 in) tall and weighs 47kg (103 lb); BMI is 17 kg/m2. Her temperature is 36.7°C (98.1°F), pulse is 90/min, respirations are 18/min, and blood pressure is 114/68 mmHg. Physical examination shows scleral icterus and a liver span of 16 cm. The spleen is not palpable. Serum studies show: Which of the following is the most likely outcome of this patient's infection?

  

  A. Complete resolution of infection

  B. Latent infection with intermittent viremia

  C. Lifelong persistent infection

  D. Patient death from acute infection

  Correct Answer: C

• Question 469:

  A 57-year-old man receives radiation therapy for a squamous cell carcinoma of the lung. Despite therapy, the tumor progressively increases in size, and he dies 6months later. His tumor cells contain a point mutation in the p53 gene (TP53), leading to an inactive gene product. Based on this finding, the progressive tumor growth despite irradiation therapy is most likely to be related to a defect in cell cycle arrest in which of the following phases of the cell cycle?

  A. G0

  B. G1

  C. G2

  D. M

  E. S

  Correct Answer: B

• Question 470:

  A 55-year-old man comes to the physician for a routine physical examination. He is currently taking no medications. His pulse is 80/min, and blood pressure is 165/95 mmHg. Physical examination shows no other abnormalities. The presence of which of the following mechanisms is most likely to increase this patient's blood pressure further?

  A. Decreased cardiac output

  B. Decreased pulse

  C. Decreased stroke volume

  D. Increased peripheral vascular resistance

  E. Increased pulmonary artery pressure

  Correct Answer: D