USMLE USMLE-STEP-2 Online Practice Questions and Exam Preparation

USMLE USMLE-STEP-2 Online Questions & Answers

• Question 471:

  Select the appropriate incubation period of the Rubella infectious disease of childhood.

  A. 16 days
  B. 78 days
  C. 810 days
  D. 1021 days
  E. 3050 days
  F. 120180 days
  D. 1021 days

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  Explanation

  The incubation period for diphtheria is 17 days. The incubation period for chicken pox is 1021 days, average 14. Infectious mononucleosis, caused by the Epstein-Barr virus, has an estimated incubation period of 3050 days. The incubation period following infection by the mumps virus is usually 1618 days but, like chicken pox, may vary from 14 to 25 days. Pertussis has a shorter incubation period, usually 710 days, with a variation of 421 days. The usual period from contamination with tetanus spores to clinical symptoms is generally 68 days. For rubella, the incubation period is from 14 to 21 days, but usually ranges from 16 to 18 days.

• Question 472:

  Catfish caught in a freshwater stream in Florida has been identified as exceeding the action level for polychlorinated biphenyls in fish (PCBs). Which regulatory agency is responsible for defining these action levels?

  A. Food and Drug Administration (FDA)
  B. United States Department of Agriculture (USDA)
  C. Environmental Protection Agency (EPA)
  D. United Nations Food and Agriculture Organization (FAO)
  E. World Health Organization (WHO)
  C. Environmental Protection Agency (EPA)

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  Explanation

  In the United States, the organization of food and water control is complex. Among the federal control agencies, the EPA is the most recent, and in many ways the most active and powerful. This agency has now set up an elaborate system of regulation and control of the use of pesticides (which until 1970 was the responsibility of the USDA) and has banned the marketing of chlorphenothane (DDT) for use in the home. The FDA has authority to remove food from the market if it contains pesticides (e.g., PCBs in fish) in excess of the action levels set by the EPA. The FDA also retains the authority to remove from the market any food with inappropriate additives, that contains substances harmful to human health, that is stored in unsanitary conditions, that has decomposed, or that is not fit for consumption.

  The USDAenforces wholesomeness standards that it sets for the production and sale of meat. International control is assisted by the WHO. This agency has mounted control programs for the eradication of communicable disease with conspicuous success in the case of smallpox. It also publishes the International Statistical Classification of Disease (ICD-9).

• Question 473:

  A 7-month-old patient presents with a history of 3 days of fever to 104°F, which resolved the same day that an exanthem erupted. The exanthema is prominent on the neck and trunk. It is macular, with discrete lesions 35 mm in diameter.

  Which of the following is the most likely diagnosis?

  A. erythema infectiosum
  B. measles
  C. roseola infantum
  D. rubella
  E. scarlet fever
  C. roseola infantum

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  Explanation

  Roseola infantum, or sixth disease, is a common acute illness of young children. Human herpesvirus 6 is the most common etiologic agent. The rash of erythema infectiosum presents initially on the face. It is intensely red with a "slapped-cheek" appearance. Rubella and measles are not commonly seen because of routine vaccination. The rash of scarlet fever is on the trunk and is described as sandpaper like.

• Question 474:

  An 11-month-old girl presents to your office with a fever of 39°C she has had for 2 days. She has also vomited frequently and had decreased fluid intake. She looked tired and ill but on examination, had no apparent source of infection. She appeared to be 510% dehydrated. Her urinalysis shows a urine specific gravity of 1.030, trace blood, and protein. Nitrite and leukocyte esterase are both positive. Microscopic examination of unspun urine shows >100 white blood cells (WBCs) and 05 red blood cells (RBCs) per high-power field, as well as many bacteria. Aurine culture is sent. Which of the following is the most appropriate management plan?

  A. Treat only if the culture is positive.
  B. Admit for intravenous (IV) hydration and IV antibiotics.
  C. Treat with intramuscular ceftriaxone and have her follow-up in the office the following day.
  D. Treat with trimethoprimsulfamethoxazole, and have her followup in the office the following day.
  E. Prescribe amoxicillin and start oral hydration.
  B. Admit for intravenous (IV) hydration and IV antibiotics.

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  Explanation

  Urine for urinalysis and culture must be properly obtained. Catheterization is the most reliable method of the choices offered. Suprapubic tap is considered the "gold-standard" but is not always technically feasible, especially in an outpatient office setting. Amidstream, clean catch specimen would be acceptable in an older, toilet-trained child. "Bagged" specimens are not recommended because of possible skin or fecal contamination of the specimen. Similarly, obtaining a sample from a diaper or potty would be unacceptable. Urinalysis includes dipstick method and microscopic examination. Leukocyte esterase (an enzyme in WBC) and nitrites suggest probable infection. Microscopic analysis of unspun urine for WBC (>10/ highpower field) or bacteria is also predictive of infection. RBCs are often present in a UTI. The patient is vomiting and dehydrated; this may indicate possible pyelonephritis. The most appropriate course would be IV hydration and empiric treatment with antibiotics (ceftriaxone) while awaiting cultures. Children with pyelonephritis are at increased risk of renal scarring, especially younger children, and should be treated early. E. coli is the most common organism cultured; others include Proteus, Klebsiella, S saprophyticus, and Enterococcus. The occurrence of a UTI in a girl under age 35 years and in a boy of any age may be a marker for an underlying congenital anatomic abnormality, in particular, vesicourethral reflux. Radiologic investigation with renal ultrasound and VCUG is recommended

• Question 475:

  For which of the following circumstances would you consider initiating chelation, such as with CaEDTA, to treat workers for workplace exposure to lead and other heavy metals?

  A. as prophylaxis for all employees exposed to metal dust and fumes
  B. only after waiting for toxic effects of heavy metal exposure to resolve on their own
  C. only for patients with symptomatic disease
  D. when metal is being absorbed through the gastrointestinal (GI) tract
  E. when patients remain in a workplace where exposure occurs
  C. only for patients with symptomatic disease

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  Explanation

  Chelating drugs are given as treatment for symptomatic poisoning by lead and other heavy metals. They should not be given prophylactically, since the agents themselves have some possible toxic side effects. These toxic effects may add to those already caused by ingestion of the metals and may actually increase absorption of the metal. For these reasons, advice should be given to workers to seek employment away from exposure to the offending agent while therapy continues. Removal from exposure is essential if levels are high.

• Question 476:

  A 53-year-old woman with five adult children complains of losing urine shortly after coughing or jumping. She occasionally loses urine while lying in bed if she happens to cough vigorously. She is unable to stop the urine once it has begun to flow.

  Which of the following would most likely confirm the cause of this woman's incontinence?

  A. a urine culture
  B. a Q-tip test
  C. urethroscopy
  D. urethrocystometry
  E. an intravenous pyelography (IVP)
  D. urethrocystometry

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  Explanation

  Although a urine culture is a standard part of the evaluation of women with loss of urine, this woman's history is not consistent with acute cystitis. AQ-tip test is done to assess the angle the urethra makes with the horizontal in the relaxed and voiding circumstances. Though intended to differentiate GSI from other causes of incontinence, it has not proved to be sufficiently sensitive to make this distinction reliably. Urethroscopy is appropriate if a urethrovaginal fistula or urethral diverticulum is suspected.

  Urethrocystometry is one name for a test that measures the pressure-volume relationship in the bladder. It should be done in most women with incontinence as the most sensitive test to distinguish the various causes of incontinence. An IVP is of little value in determining the cause of incontinence.

• Question 477:

  A 75-year-old man is brought to the emergency department for severe pain in the left flank and back of 1 hour duration. He has a prior history of a myocardial infarction and coronary artery bypass grafting 8 years ago. On examination, he is found to have a BP of 80/50 mmHg, pulse rate of 110/min, respiratory rate of 15/min, and a pulsatile, tender abdominal mass. He has had two large-bore IV lines placed by the paramedics. He is alert and oriented, and gives consent for surgery. Which of the following is the most appropriate next step in management of this patient?

  A. immediate consultation with cardiology to assess cardiac risk for surgery, followed by transfer to the operating room
  B. resuscitation in the emergency department with IV fluids, transfer to radiology for a CT scan to assess for the location and degree of rupture, followed by transfer to the operating room
  C. resuscitation in the emergency department with IV fluids to achieve a systolic BP greater than 100, followed by transfer to the operating room
  D. immediate transfer to the operating room with concomitant resuscitation and laparotomy
  E. resuscitation in the emergency department with IV fluids, transfer to radiology for immediate aortic angiogram for assessment of the location of the rupture, followed by transfer to theoperating room
  D. immediate transfer to the operating room with concomitant resuscitation and laparotomy

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  Explanation

  The clinical manifestations of ruptured abdominal aneurysm are back, flank, or abdominal pain; hypotension; and a pulsatile abdominal mass. The treatment should be immediate transfer to the operating room for laparotomy. Ultrasound can be done quickly in the ER to confirm the diagnosis. If the patient is hemodynamically stable, and the diagnosis is in doubt, a CT scan can be performed, but is generally not needed. Angiogram is not indicated unless endovascular repair is being considered, and then it should be performed in the operating room. Following successful treatment, diarrhea may suggest ischemic colitis, and urgent sigmoidoscopy is indicated. Adelay in diagnosis of bowel ischemia caused by numerous other diagnostic tests may increase the mortality rate. If bowel ischemia is found, immediate colon resection should be undertaken.

• Question 478:

  A 23-year-old pregnant woman at 5 postmenstrual weeks took coumadin until about 3 days after her menses was due. She has monthly menses. A home pregnancy test was positive on the day she took coumadin. She takes coumadin because of a history of deep vein thrombosis and pulmonary embolism. She is concerned that the coumadin will cause birth defects.

  You tell her that the conceptus is most susceptible to teratogenesis at what stage of pregnancy?

  A. between menses and ovulation
  B. from ovulation to implantation
  C. between implantation and the day of expected menses
  D. between the day of expected menses and 12 postmenstrual weeks
  E. during the second and third trimesters
  D. between the day of expected menses and 12 postmenstrual weeks

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  Explanation

  The conceptus is remarkably resistant to the toxic and teratogenic effects of most drugs until about 2 postconceptual weeks (4 postmenstrual weeks). Although certain drugs may be toxic to oocytes, their effect will be to prevent conception or cause an early spontaneous abortion. The developing conceptus is not exposed to maternal toxins or teratogens until after implantation and establishment of a blood supply from mother to fetus. Even after implantation, the fetus is relatively resistant to teratogens for about 1 week. Organogenesis is complete by the end of the first trimester. Congenital abnormalities are, therefore, unlikely in the second and third trimesters.

• Question 479:

  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
  D. avoidance of vaccine-associated paralytic poliomyelitis

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  Explanation

  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 480:

  A 45-year-old man presents to the physician's office for evaluation of a posterior neck mass. The mass has been present for years, but has slowly enlarged over the last 2 years. Examination reveals a subcutaneous mass that is soft, nontender, and movable. For the above patient with a neck mass, select the most likely diagnosis.

  A. thyroid carcinoma
  B. cystic hygroma
  C. acute suppurative lymphadenitis
  D. thyroglossal duct cyst
  E. lipoma
  F. carotid artery aneurysm
  G. mixed parotid tumor (pleomorphic adenoma)
  H. laryngeal carcinoma
  I. parathyroid adenoma
  J. branchial cleft cystK. tuberculosis
  E. lipoma

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  Explanation

  Lipomas present as soft, subcutaneous masses that arise in all areas of the body. They are treated by simple excision.