USMLE USMLE Certifications USMLE Questions & Answers

• Question 441:

  A 65-year-old male who had a cholecystectomy at a local hospital experiences nausea and vomiting two days later. He is prescribed metoclopramide by the resident physician. Metoclopramide is contraindicated in patients with:

  A. coronary artery disease

  B. liver cirrhosis

  C. migraine headaches

  D. Parkinson disease

  E. urinary tract infections

  Correct Answer: D

  Explanation:

  This patient most likely has post-surgery gastroparesis. Metoclopramide is a D_2 receptor antagonist which increases intestinal motility, contractility and lower esophageal sphincter tone. It also promotes gastric emptying. Metoclopramide is commonly used to treat diabetic and post-surgical gastroparesis, gastroesophageal reflux disease and chemotherapy induced nausea and vomiting. Its side effects include parkinsonism, tardive dyskinesia, diarrhea, depression and restlessness. It is contraindicated in patients with Parkinson disease and small bowel obstruction.

• Question 442:

  A 17-year-old female is brought to the emergency department by her parents due to right foot pain. She denies recent trauma and has no history of major illnesses. She is physically active and walks for at least one hour daily. She says that she is doing well in high school and gets along well with her parents except that they keep telling her to eat more especially since her boyfriend broke up with her a year ago. Vitals reveal a weight 47.6 kg (105 lbs) and BMI of16 kg/m². The most likely diagnosis is

  A. conversion disorder

  B. depressive disorder

  C. gonococcal arthritis

  D. injured medial ankle tendon

  E. metatarsal fracture

  Correct Answer: E

  Explanation: This patient's low BMI and a year long history of poor eating habits are consistent with anorexia nervosa. Anorexic patients have an unreasonable fear of gaining weight and “feel fat" even when overweight and engage in prolonged physical activity in order to lose weight. This patient most likely started eating poorly after her breakup with her boyfriend. Metatarsal stress fractures are a complication of rigorous physical activity in patients with anorexia due to chronic malnourishment which results in low bone density. Other findings include amenorrhea, electrolyte disturbances, lanugo, anemia and coexisting depression. Psychotherapy and nutritional rehabilitation are first line treatments.

• Question 443:

  A 35-year-old female comes to the physician due to headaches of two months’ duration. She has no history of pre-existing medical illnesses. Vital signs are within normal limits. A head CT reveals a mass above the left petrous bone and biopsy reveals a malignant schwannoma on the left trigeminal nerve. The patient undergoes surgery for resection of the mass. If there is damage to the involved nerve during the surgery, there will be

  A. decreased accommodation in the left eye

  B. decreased corneal reflex in the left eye

  C. decreased gag reflex

  D. decreased taste from the anterior two thirds of the tongue

  E. inability to adduct the left eye

  Correct Answer: B

  Explanation:

  The trigeminal nerve (CN V) is a mixed (sensory and motor) nerve. It provides sensory innervation to the face, cornea, mucous membranes of the nasal and oral cavities, frontal sinus, anterior two-thirds of the tongue, teeth, and hard palate. It also provides motor innervation for the muscles of mastication (temporalis, masseter, lateral and medial pterygoids). If this patient's left trigeminal nerve is injured during surgery, she could lose the corneal reflex on the left. The afferent (sensory) limb for this reflex is transmitted by CN V (unilaterally) and the efferent (motor) limb (bilaterally) is transmitted by the facial nerve, CN VII. Additional symptoms that patient could also have include left facial anesthesia, ipsilateral flaccid paralysis of muscles of mastication, deviation of the jaw to the left, hypoacusis and trigeminal neuralgia.

• Question 444:

  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 exposure of a fetus to ciprofloxacin can result in:

  A. cartilage damage

  B. discolored teeth

  C. gray baby syndrome

  D. kernicterus

  E. ototoxicity

  Correct Answer: A

  Explanation:

  Fluoroquinolones are a class of antibiotics which work by inhibiting topoisomerase II 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 445:

  A 61-year-old male is admitted to the hospital with worsening shortness of breath and fatigue. Physical examination reveals dullness to percussion and decreased breath sounds in the right lung. A chest x-ray is obtained which reveals a large right-sided pleural effusion. Thoracentesis yields 250 mL of fluid with a pleural fluid protein/serum protein ratio of 0.7 and a lactate dehydrogenase level of 240 U/L. The most likely diagnosis is:

  A. bacterial pleuritis

  B. cirrhosis of the liver

  C. congestive heart failure

  D. nephrotic syndrome

  E. protein losing enteropathy

  Correct Answer: A

  Explanation:

  Exudative effusions are characterized by one or more of the following: pleural fluid protein/serum protein ratio > 0.5, pleural fluid LDH/serum LDH ratio > 0.6, or pleural fluid LDH more than two-thirds the normal upper limit for serum (Light's criteria). An exudate results from leakage of protein-rich fluid from the plasma into the interstitium. It is usually the result of increased vascular permeability caused by inflammation. Exudates also contain numerous acute or chronic inflammatory cells, depending on the inciting event. When the pleural effusion is unilateral, always consider a bacterial cause. Of the listed options, only bacterial pleuritis would produce an exudate. If pleuritis is caused by pyogenic organisms, the exudate is purulent (neutrophil-rich). If pleural inflammation is due to mycobacterial infection or neoplastic infiltration, the resulting exudate will contain chronic inflammatory cells such as lymphocytes, macrophages.

• Question 446:

  A 45-year-old male is brought to the emergency department by the police who found him wandering around a park at midnight. Physical examination reveals bilateral hand tremors. Laboratory tests reveal elevated serum gamma-glutamyl transferase. Thirty hours after he is admitted to the hospital he develops generalized seizures. The most appropriate treatment for this patient's seizures is

  A. carbamazepine

  B. lorazepam

  C. phenytoin

  D. thiopental

  E. zolpidem

  Correct Answer: B

  Explanation:

  The patient is most likely experiencing alcohol withdrawal. Signs of alcohol intoxication include ataxia, slurred speech and emotional lability. Laboratory findings sensitive for alcohol use include serum gammaglutamyl transferase (GGT) and an AST to ALT ratio greater than 2:1 in chronic alcoholics. Alcohol withdrawal may present with tremors, insomnia, diaphoresis, agitation, delirium tremens 48–96 hours after the last drink, alcoholic hallucinosis 12–48 hours after the last drink and withdrawal seizures 6-48 hours after the last drink. The treatment of these seizures is with a benzodiazepam such as lorazepam.

• Question 447:

  A 45-year-old female comes to the physician with joint pain, swelling and morning stiffness which improves with use. She also reports weight loss of 3 kg (6.6 lbs). Laboratory tests reveal the presence of serum rheumatoid factor. The most likely other finding in this patient is:

  A. anti-acetylcholine receptor antibodies

  B. anti-centromere antibodies

  C. anti-cyclic citrullinated peptide antibodies

  D. anti-smooth muscle antibodies

  E. anti-U1 ribonucleoprotein antibodies

  Correct Answer: C

  Explanation:

  This patient most likely has rheumatoid arthritis (RA) which is an autoimmune disease characterized by inflammation and erosion of articular cartilage and bone. It presents with weight loss, fatigue, joint pain, swelling and morning stiffness which lasts longer than an hour and improves with use. It usually involves the metacarpophalangeal joints, proximal interphalangeal joints and the wrist joints. Laboratory findings in patients with RA include IgM antibodies against the Fc region of IgG (rheumatoid factor), HLA-DR4 and anti-cyclic citrullinated peptide antibodies which are more specific for RA. Synovial fluid analysis also reveals joint inflammation unlike in osteoarthritis which is non-inflammatory. Management of RA includes treatment with NSAIDs, glucocorticoids, methotrexate, leflunomide, hydroxychloroquine and biologic agents like TNF-alpha inhibitors such as etanercept.

• Question 448:

  A 35-year-old male comes to the physician due to fatigue. He recently returned from a trip to Japan. Laboratory results are as follows:

  Hemoglobin – 9 g/dL Mean corpuscular volume – 108 fl MCHC – 33 g/dL Mean corpuscular hemoglobin – 35 pg A peripheral blood smear is obtained which reveals enlarged red blood cells and hyper segmented neutrophils. If these findings were caused by an infection, the most likely source of the infection is via:

  A. blackfly bite

  B. dog feces

  C. raw fish

  D. snails

  E. undercooked pork

  Correct Answer: C

  Explanation:

  Diphyllobothrium latum is a tapeworm which can cause vitamin B12 deficiency because it competes for this vitamin in the small intestine. Infection with this tapeworm occurs after consumption of raw or undercooked freshwater fish. Vitamin B12 deficiency may occur in infected patients and presents with fatigue due to the macrocytic megaloblastic anemia with hyper segmented neutrophils. Treatment of the infection is with praziquantel.

• Question 449:

  A 40-year-old male is brought to the emergency department due to progressive memory loss, confusion, and urinary incontinence. Laboratory studies reveal a CD4 cell count of 25/mm³. A MRI reveals moderate brain atrophy. Although the patient is admitted for treatment he eventually dies of disseminated aspergillosis. Microscopic examination of an autopsy specimen from his brain shows multifocal lymphohistiocytic infiltrates with numerous microglial nodules and scattered multinucleated giant cells. His histologic and MRI findings were most likely caused by

  A. aspergillosis

  B. HIV encephalitis

  C. mycobacterial infection

  D. progressive multifocal leukoencephalopathy

  E. vacuolar myelopathy

  Correct Answer: B

  Explanation:

  Patients with AIDS and a CD4 cell count of 25/mm³ can develop many complications, including opportunistic infections, lymphomas, polyneuropathies, and subacute encephalitis. HIV gains access to the CNS through incoming macrophages and may cause a subacute inflammation of the brain parenchyma known as HIV encephalitis, which typically occurs in AIDS patients with CD4 counts less than 200/mm³. The presence of multinucleated giant cells is typical of HIV encephalitis.

• Question 450:

  A 9-month-old male is evaluated for lactic acidosis and increased levels of serum alanine. He is diagnosed with pyruvate dehydrogenase complex deficiency and placed on a special diet by the physician. This special diet most likely consists of

  A. alanine

  B. asparagine

  C. histidine

  D. leucine

  E. serine

  Correct Answer: D

  Explanation: Pyruvate dehydrogenase complex deficiency (PDCD) is a neurodegenerative disorder associated with abnormal mitochondrial metabolism. It can present in infants with hypotonia, poor feeding, lethargy, seizures, elevated serum alanine and lactic acidosis. Management is with ketogenic diets such as meals with increased lysine and leucine content and high fat intake.