USMLE USMLE Certifications USMLE-STEP-3 Questions & Answers

• Question 441:

  A 4-year-old girl is brought in to the office by her mother. She developed chicken pox about 6 days ago. She appeared to be recovering well but mother became concerned because she was persistently scratching at several of the lesions and they were not healing. On examination, the child is afebrile and generally well appearing. On examination of her skin you see the following image What is the most likely responsible agent?

  

  A. Trichophyton rubrum

  B. poison ivy

  C. human papilloma virus

  D. GAS

  E. varicella-zoster virus

  Correct Answer: D Section: (none)

  Explanation:

  The image provided shows a classic case of impetigo. This is a common skin infection of childhood. It frequently occurs following a case of chickenpox and is due to the child picking or scratching at the varicella lesions, resulting in a secondary bacterial infection. GAS infection is the most common cause of impetigo associated with varicella infections. It is markedly more prevalent than the next most common infectious agent, S. aureus. Tinea corporis, often due to T. rubrum, is also known as ringworm. It classically is a circular lesion with a red, raised border, and central clearing. Contact dermatitis, from exposure to an irritant such as poison ivy, often causes plaques of erythema and edema with superimposed vesicles. This is also frequently secondarily infected with GAS from scratching. Warts, caused by the human papilloma virus, do not typically appear as the lesions in the image. Of the options listed, oral cephalexin would be the most appropriate initial therapy. Most GAS isolates are sensitive to first-generation cephalosporins, such as cephalexin. Topical steroids are useful for inflammatory or allergic conditions, topical nystatin for a fungal infection (such as tinea corporis) and oral acyclovir can be used early in the course of a varicella infection

• Question 442:

  A 4-year-old girl is brought in to the office by her mother. She developed chicken pox about 6 days ago. She appeared to be recovering well but mother became concerned because she was persistently scratching at several of the lesions and they were not healing. On examination, the child is afebrile and generally well appearing. On examination of her skin you see the following image What is the most likely current diagnosis?

  

  A. tinea corporis

  B. impetigo

  C. warts

  D. contact dermatitis

  E. reactivated chicken pox

  Correct Answer: B Section: (none)

  Explanation:

  The image provided shows a classic case of impetigo. This is a common skin infection of childhood. It frequently occurs following a case of chickenpox and is due to the child picking or scratching at the varicella lesions, resulting in a secondary bacterial infection. GAS infection is the most common cause of impetigo associated with varicella infections. It is markedly more prevalent than the next most common infectious agent, S. aureus. Tinea corporis, often due to T. rubrum, is also known as ringworm. It classically is a circular lesion with a red, raised border, and central clearing. Contact dermatitis, from exposure to an irritant such as poison ivy, often causes plaques of erythema and edema with superimposed vesicles. This is also frequently secondarily infected with GAS from scratching. Warts, caused by the human papilloma virus, do not typically appear as the lesions in the image. Of the options listed, oral cephalexin would be the most appropriate initial therapy. Most GAS isolates are sensitive to first-generation cephalosporins, such as cephalexin. Topical steroids are useful for inflammatory or allergic conditions, topical nystatin for a fungal infection (such as tinea corporis) and oral acyclovir can be used early in the course of a varicella infection.

• Question 443:

  You are working in a community clinic on a Native American reservation. A mother brings in her 8-year-old son for an ophthalmic evaluation. On examination, you find bilateral corneal ulceration and decreased visual acuity. What is the most common infectious cause of blindness in the world?

  A. HSV

  B. C. trachomatis

  C. GAS

  D. S. pneumoniae

  E. E. coli

  Correct Answer: B Section: (none)

  Explanation:

  The most common infectious cause of blindness in the world is trachoma. Trachoma is the chronic effect of a C. trachomatis infection acquired in the perinatal period. The most common cause of blindness in the world is noninfectious

• Question 444:

  You are working in the emergency department and are called to perform a lumbar puncture on a 3-monthold infant who presented with fever and lethargy. The spinal fluid that you obtain is turbid. The laboratory reports that there are 200 WBCs and 5 RBCs per high-power field (HPF). Ninety-five percent of the WBCs in the spinal fluid are neutrophils

  If the laboratory result showed that 98% of the WBCs in the spinal fluid were lymphocytes, what would be the most likely etiology of the infection?

  A. Mycobacterium tuberculosis

  B. HSV

  C. C. trachomatis

  D. RSV

  E. nonpolio enteroviruses

  Correct Answer: E Section: (none)

  Explanation:

  In children over 1 month of age, the most common causes of bacterial meningitis are S. pneumoniae and Neisseria meningitidis. HIB was also a frequent cause of this disease prior to the widespread use of the HIB vaccine. GBS, E. coli, and HSV would be more common causes of CNS infections in neonates. (McMillin et al., 1999, Chap. 142) Nonpolio enteroviruses are the most common causes of aseptic meningitis in childhood. There are approximately 65 nonpolio enteroviruses, including the Coxsackieviruses, echoviruses, and enteroviruses. Children are the main susceptible population and transmission is from child to child, via fecal-oral or oraloral (respiratory) contact. Meningitis may result from viremic spread of the virus. Treatment of this is supportive.

• Question 445:

  You are working in the emergency department and are called to perform a lumbar puncture on a 3-monthold infant who presented with fever and lethargy. The spinal fluid that you obtain is turbid. The laboratory reports that there are 200 WBCs and 5 RBCs per high-power field (HPF). Ninety-five percent of the WBCs in the spinal fluid are neutrophils.

  Which of the following is the most probable cause of this illness?

  A. GBS

  B. HSV

  C. GAS

  D. S. pneumoniae

  E. E. coli

  Correct Answer: D Section: (none)

  Explanation:

  In children over 1 month of age, the most common causes of bacterial meningitis are S. pneumoniae and Neisseria meningitidis. HIB was also a frequent cause of this disease prior to the widespread use of the HIB vaccine. GBS, E. coli, and HSV would be more common causes of CNS infections in neonates. (McMillin et al., 1999, Chap. 142) Nonpolio enteroviruses are the most common causes of aseptic meningitis in childhood. There are approximately 65 nonpolio enteroviruses, including the Coxsackieviruses, echoviruses, and enteroviruses. Children are the main susceptible population and transmission is from child to child, via fecal-oral or oraloral (respiratory) contact. Meningitis may result from viremic spread of the virus. Treatment of this is supportive.

• Question 446:

  A 4-year-old is brought to your office by his mother for evaluation. She is concerned because the child has been spiking fevers and pulling on his left ear. Your examination reveals a bulging and erythematous tympanic membrane (TM).

  You determine that the child should receive antibiotics. The initial antibiotic of choice should be?

  A. amoxicillin

  B. azithromycin (Zithromax)

  C. erythromycin

  D. trimethoprim/sulfamethoxazole (Septra)

  E. tetracycline

  Correct Answer: A Section: (none)

  Explanation: The most common cause of otitis media in children is pneumococcus (S. pneumoniae). This is also the most common cause of sinusitis and pneumonia. Otitis media is usually seen in conjunction with an upper respiratory tract infection. Pressure from extensive use of antimicrobials has resulted in a dramatic increase in penicillin resistance in pneumococcus. Amoxicillin remains the recommended initial antibiotic of choice for the treatment of otitis media in children. In an effort to reduce the incidence of antibiotic resistance, and because of the high spontaneous cure rate of otitis media, many authorities are advocating withholding antimicrobial treatment unless symptoms persist for several days in spite of symptomatic treatment.

• Question 447:

  Which of the following has a carrier state that is not considered contagious?

  A. E. coli

  B. HSV

  C. Chlamydia trachomatis

  D. GAS

  E. RSV

  Correct Answer: D Section: (none)

  Explanation:

  GAS pharyngitis ("strep throat") is a common cause of tonsillitis requiring antibiotics. GAS continues to be very susceptible to penicillin, which still remains the treatment of choice. Occasionally, children will have a persistently positive throat culture for GAS and are considered carriers. This carrier state is not a risk for rheumatic disease and is felt not to be contagious to others. The presence of E. coli in the intestinal tract is considered colonization and not carrier state. An example of an enteric bacterium which does have a carrier state would be Salmonella typhi (typhoid fever).

• Question 448:

  A 4-year-old is brought to your office by his mother for evaluation. She is concerned because the child has been spiking fevers and pulling on his left ear. Your examination reveals a bulging and erythematous tympanic membrane (TM).

  Which of the following is most likely to be the cause of his illness?

  A. Haemophilus influenzae, type B (HIB)

  B. Moraxella catarrhalis

  C. Mycoplasma pneumoniae

  D. GAS

  E. S. pneumoniae

  Correct Answer: E Section: (none)

  Explanation:

  The most common cause of otitis media in children is pneumococcus (S. pneumoniae). This is also the most common cause of sinusitis and pneumonia. Otitis media is usually seen in conjunction with an upper respiratory tract infection. Pressure from extensive use of antimicrobials has resulted in a dramatic increase in penicillin resistance in pneumococcus. Amoxicillin remains the recommended initial antibiotic of choice for the treatment of otitis media in children. In an effort to reduce the incidence of antibiotic resistance, and because of the high spontaneous cure rate of otitis media, many authorities are advocating withholding antimicrobial treatment unless symptoms persist for several days in spite of symptomatic treatment.

• Question 449:

  You are called to see a 12-hour-old male infant who was born to a 19-year-old G1 woman with no prenatal care. She presented to the emergency room completely dilated and crowning. The baby was born minutes later. On examination, the baby is febrile and tachypneic. A CXR confirms the presence of pneumonia.

  What is the most likely infectious agent?

  A. group B Streptococcus (GBS)

  B. HSV

  C. E. coli

  D. respiratory syncytial virus (RSV)

  E. Streptococcus pneumoniae

  Correct Answer: A Section: (none)

  Explanation: GBS is the most common cause of infection in the newborn infant, followed by E. coli and L. monocytogenes. GBS is the most common cause of pneumonia, septicemia, UTI, and meningitis. The risk of early-onset (within the first 7 days of life) GBS infection can be reduced with the antenatal administration of appropriate antimicrobials. The use of perinatal antimicrobials has no effect on the occurrence of late-onset (after 7 days of life) GBS disease.

• Question 450:

  On a Monday morning you see a 12-year-old otherwise healthy boy in the emergency department. The parents brought the boy in because they noticed that he started to have an abnormal gait in the past few days. He seems to be shuffling his feet. The boy complains that his legs feel heavy and are tingling. He relates that his arms feel fine. His past history is significant for attention deficit/hyperactivity disorder (ADHD) for which he is taking methylphenidate. He denies trauma or taking any other medicines or drugs. On examination, he is afebrile with normal vital signs. His entire physical examination is normal with the exception of the examination of is lower extremities. He has 3/5 strength throughout both of his lower extremities with a normal muscle mass. His all joints have a full range of motion, without any pain or swelling. His reflexes are absent and he describes some paresthesias of his feet and ankles

  Which of the following is the most appropriate initial management plan?

  A. hospitalization and close observation for progression of his weakness

  B. high-dose corticosteroids

  C. gastric lavage and activated charcoal

  D. outpatient family counseling

  E. plasmaphoresis

  Correct Answer: A Section: (none)

  Explanation: Acute inflammatory demyelinating polyneuropathy, commonly called Guillain-Barré syndrome, is an ascending paralysis with a hallmark of absent reflexes. There may also be some nominal sensory deficits as well, but they are not as striking as the paresis. Methylphenidate toxicity usually results in seizures and tachycardia. In children with malingering, reflexes are usually present, as they are not under cognitive control. Reflexes are also present in children with polymyositis. Children with polymyositis will usually have fever and muscle pain with weakness, as well. With the use of the polio vaccines (OPV or IPV), poliomyelitis is no longer present in wild type in the United States. Guillain-Barré is usually a self-limited disease. The most common complication is respiratory failure. The paresis usually advances for 4872 hours and then will slowly recede. The use of corticosteroids is not recommended. Plasmaphoresis is used in the following situations: progressive paresis, nonambulatory patients, or bulbar or respiratory involvement. As this child's disease has plateaued at the time of evaluation, plasmaphoresis would be of little benefit.