USMLE USMLE Certifications USMLE-STEP-2 Questions & Answers

• Question 471:

  A13-year-old girl presents with lethargy, fever, severe headache, and a stiff neck. On examination, a unilateral fixed, dilated pupil and papilledema are noted. Which of the following is the most appropriate initial step in managing this patient?

  A. administration of IV cefotaxime

  B. administration of IV mannitol

  C. CT of the head

  D. intubation and hyperventilation

  E. performance of a lumbar puncture

  Correct Answer: D

  This case most likely represents an adolescent with meningitis who has developed increased intracranial pressure. Intubation and hyperventilation is indicated immediately. Hyperventilation is the most appropriate immediate, nonsurgical treatment of intracranial hypertension. By hyperventilating this patient, you will decrease the PCO2, resulting in vasoconstriction in the CNS. Decreasing the PCO2 510 mmHg will decrease intracranial pressure 2530%. Administering antibiotics, preferably after blood cultures are obtained, is appropriate. Obtaining a CT scan of the head may reveal intracranial lesions which require additional therapy. Mannitol given intravenously also is a highly effective means for lowering intracranial pressure. Mannitol does not cross the blood-brain barrier. It remains in the capillaries and creates an osmotic gradient, causing fluid to shift from intracellular spaces to the vasculature, thereby decreasing intracranial pressure. Although a lumbar puncture may be necessary eventually, it is contraindicated as initial management because of the possibility of brain stem herniation

• Question 472:

  Routine examination of an otherwise healthy kindergarten child with a history of asthma reveals a BP of 140/90 mmHg. Which of the following is the most likely cause of the hypertension?

  A. theophylline toxicity

  B. chronic lung disease

  C. renal disease

  D. coarctation of the aorta

  E. obesity

  Correct Answer: C

  The most common causes of hypertension in young children are renal in origin. Polycystic kidney disease, congenital vascular anomalies, tumors, and infections all are causes. Urologic evaluation is imperative for the child described in the question. Theophylline toxicity that is severe enough to elevate BP significantly would be unlikely in the absence of jitteriness, nausea, or tachycardia. Chronic lung disease would not elevate the systemic BP in an otherwise healthy child. Coarctation of the aorta is a less common cause of hypertension in this age group. BPs taken on all extremities would be helpful in the diagnosis.

• Question 473:

  A 7-year-old child is scheduled for an elective tonsillectomy. The most important instruction to the parents should be to make sure that the child does which of the following?

  A. avoids contact with other children

  B. discontinues antibiotics 72 hour before surgery

  C. avoids aspirin and antihistamines for 2 weeks before surgery

  D. does not drink from siblings' cups

  E. eats iron-laden foods for 3 weeks before surgery

  Correct Answer: C

  Aspirin and antihistamines have been shown to adversely affect platelet aggregation, leading to increased bleeding time. Moreover, this effect may persist for 710 days after discontinuing these medications. When possible, children undergoing surgery should not be receiving aspirin or antihistamines. The use of antibiotics would not be a contraindication to elective surgery. Children undergoing elective surgery should be free of respiratory infection. It is prudent to counsel the parents in ways to minimize infection, but avoiding social contacts and shared eating utensils would likely have little effect in the case described in the question. A child should be free of anemia before elective surgery, but eating iron-rich foods would not significantly elevate Hb in a short period of time.

• Question 474:

  An infant is due for her first dose of polio vaccine.Her parents have heard that there are two different types of vaccine for polio. They want to know why their daughter needs to get another shot rather than just taking the oral form of the vaccine. You tell the parents the major advantage of the injectable vaccine is which of the following?

  A. lower cost

  B. increased mucosal immunity

  C. better efficacy

  D. avoidance of vaccine-associated paralytic poliomyelitis

  E. boosting her immunity through secondary transmission

  Correct Answer: D

  In 1997, the expanded use of IPV in the United States began. Before this, the risk of vaccine-associated paralytic polio was 1 case per 2.4 million doses of oral polio vaccine (OPV); the rate after the first dose was 1 per 750,000 doses, including vaccine recipient and contact cases. This is the main disadvantage of the OPV vaccine. Although it is contraindicated in children or their contacts with immunodeficiencies, they are at high risk in case of inadvertent exposure, because there is feco-oral transmission of the virus for 46 weeks after the vaccine is given. The advantages of the OPV include lower cost, fewer "shots," and boosting herd immunity. The OPV vaccine is still recommended for global polio eradication.

• Question 475:

  A9-year-old boy presents with a several-day history of progressive arm and leg weakness. He has been well except for an upper respiratory infection 2 weeks ago. The patient is alert and oriented. On repeated examination, the heart rate varies between 60 and 140 beats/min, and the blood pressure (BP) varies between 90/60 and 140/90 mmHg. Respirations are shallow, with a rate of 50/min. There is symmetric weakness of the face and all four extremities. Deep tendon reflexes are absent. Sensation is intact.

  Which of the following is the most likely diagnosis?

  A. polymyositis

  B. myasthenia gravis

  C. transverse myelitis

  D. Guillain-Barr?syndrome

  E. viral encephalitis

  Correct Answer: D

  Progressive, symmetric motor weakness, areflexia, and autonomic instability, with mild or absent sensory signs, are typical features of Guillain-Barr?syndrome. Frequently, there is a history of infection (often respiratory) in the several weeks preceding clinical onset of the syndrome. Supportive evidence for the diagnosis includes elevation of CSF protein concentration with a mild (10 or fewer cells/mL) mononuclear pleocytosis, and slowing of nerve conduction velocities. In polymyositis, deep tendon reflexes would be intact. Myasthenia gravis is characterized by weakness aggravated by repetitive movement. In transverse myelitis, sensation would also be lost. Viral encephalitis is characterized by mental status abnormalities.

• Question 476:

  A1-year-old child with ALL in remission for 3 months is in the office for a health maintenance visit. He is due for multiple vaccinations including hepatitis B vaccine, inactivated polio vaccine (IPV), varicella vaccine

  A. influenzae B vaccine (Hib), and pneumococcal vaccine (PCV). You remember that some of these vaccines are live attenuated viruses and are contraindicated in immunocompromised patients. Which vaccine will you not give to this patient?

  B. PCV

  C. varicella vaccine

  D. hepatitis B vaccine

  E. Hib

  F. IPV

  Correct Answer: B

  Varicella vaccine is a live vaccine. All others are killed vaccines. Diphtheria and tetanus are both toxoids, the others are from killed microorganisms.

• Question 477:

  An 18-month-old girl is brought to the hospital with a history of 6 days of bloody diarrhea. She has been drinking well but has not been wetting her diaper. She has been irritable. On physical examination, she has periorbital edema. She appears pale and is tachycardic. Her CBC shows a hemoglobin of 6 g/dL and a platelet count of 100,000/mm3. Her blood urea nitrogen (BUN) is 50 mg/dL and creatinine is 5.5 mg/dL. Her urinalysis shows gross hematuria. Which of the following is the most likely causative organism for her clinical problem?

  A. E. coli 0157:H7

  B. group A Streptococci

  C. group B Streptococci (GBS)

  D. S. aureus

  E. the cause of this illness is not known

  Correct Answer: A

  The child most likely has hemolytic-uremic syndrome. This illness is most common in children under 2

  years old. They present with a prodromal illness, bloody diarrhea, and then a sudden onset of lethargy and

  pallor when the hemolytic anemia occurs. Coincident with this is the development of acute renal failure,

  often with low urine output. E. coli 0157:H7 is the most common organism in the United States. Group A

  Streptococci are associated with poststreptococcal acute glomerulonephritis.

  Thrombocytopenia and anemia are not seen in this disease.

• Question 478:

  A 7-year-old boy presents with a rash. His mother states that he was well until 3 days ago when he developed fever and malaise. The next day, the rash started as papules on the trunk, which rapidly changed to vesicles. The lesions have spread all over the body. On physical examination, he has no fever and seems well. You note numerous vesicles all over the body, some of which have crusted over. Which of the following is the most likely diagnosis?

  A. chicken pox

  B. Kawasaki disease

  C. measles

  D. rubella

  E. staphylococcal scalded skin syndrome

  Correct Answer: A

  This is a typical presentation of chicken pox. A prodrome of fever and malaise is followed by the rapid eruption of papules that turn to vesicles and crust over. The rash in measles, rubella, and Kawasaki disease are macular or maculopapular. In staphylococcal scalded skin syndrome, a diffuse, tender erythroderma develops

• Question 479:

  A5-week-old bottle-fed boy presents with persistent and worsening projectile vomiting, poor weight gain, and hypochloremic metabolic alkalosis. Of the following diagnostic modalities, which would most likely reveal the diagnosis?

  A. ultrasound of abdomen

  B. barium enema

  C. evaluation of stool for ova and parasites

  D. testing well water for presence of nitrites

  E. serum thyroxine

  Correct Answer: A

  The case presented is classic of pyloric stenosis. This results from hypertrophy and hyperplasia of smooth muscle in the stomach, causing a narrowed, even, obstructed outlet. Persistent projectile vomiting causes ongoing losses of calories and electrolytes, resulting in growth failure and hypochloremic metabolic alkalosis. Hyponatremia and hypokalemia may also be associated. Often, the diagnosis can be made by physical examination alone. However, if an olive-shaped mass is not palpated, an abdominal ultrasound may confirm the diagnosis

• Question 480:

  A 3-year-old boy was bitten while teasing a neighborhood cat. On examination, there are two puncture wounds on the right hand and some superficial scratch marks. There is erythema, warmth, and induration around the puncture sites. Which of the following organisms most likely caused the infection?

  A. Pasturella multicoda

  B. Bartonella henselae

  C. Eikenella corrodens

  D. Peptostreptococcus species

  E. alpha Streptococci

  Correct Answer: A

  P. multicoda and S. aureus are organisms commonly associated with cat bites. The cat's sharp teeth and claws predispose the victim to puncture wounds. Wound infections are more common in cat bites than dog bites. E. corrodens, Peptostreptococcus species, and alpha Streptococci are more common with human bites. B. henselae causes cat-scratch disease, which presents with subacute lymphadenitis.