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

USMLE USMLE-STEP-2 Online Questions & Answers

• Question 281:

  A 30-year-old man presents to the emergency department with sudden onset of severe epigastric pain and vomiting 3 hours ago. He reports a 6-month history of chronic epigastric pain occurring nearly every day and relieved by antacids. On examination, he appears sweaty and avoids movement. Vital signs reveal a temperature of 100°F, BP of 100/60 mmHg, pulse rate of 110/min, and respiratory rate of 12/min. The remainder of his examination reveals diminished bowel sounds and a markedly tender and rigid abdomen. A chest x-ray and abdominal films reveal pneumoperitoneum Which of the following is the most appropriate next step in management?

  A. immediate laparotomy
  B. nonoperative management with NG decompression and antibiotics
  C. fluid resuscitation
  D. administration of H2 blockers
  E. placement of a central venous line
  C. fluid resuscitation

  ---

  Explanation

  Perforated duodenal ulcer usually presents as a sudden onset of acute abdominal pain.Examination usually reveals severe abdominal tenderness with rigidity of the abdominal musculature (i.e., an acute abdomen). With a prior history of abdominal pain relieved by antacids, a chronic ulcer that has now perforated is strongly suggested. Perforated colon cancer occurs in an older age group, as well as gastric ulcer. Following plain radiographs that show pneumoperitoneum, no additional diagnostic tests are required and serve only to delay treatment. The treatment is laparotomy and either patch closure of the perforation or definitive operation, the latter being preferred, depending on operative findings. However, the patient must receive fluid resuscitation before laparotomy to avoid hypotension and its consequences. Although nonoperative management for contained perforations has been suggested by some authors, an acute abdomen is an indication for operative management.

• Question 282:

  Select the appropriate incubation period of the Mumps 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

  ---

  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 283:

  For each of the diseases listed, select the arthropod vector responsible for its transmission.

  Dengue fever

  A. aegypti
  B. Anopheles species
  C. Pediculus humanus corporis
  D. Dermacentor andersoni
  E. Sarcoptes scabiei
  A. aegypti

  ---

  Explanation

  Epidemic typhus (classical typhus fever, or louse-borne typhus) has disappeared from most areas of the world but might reappear in conditions of famine, war, or other disasters. There are small areas where it is endemic. The responsible organism, a rickettsia, is conveyed from case to case by the human body louse, P. humanus corporis. Malaria, in its various forms (Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae), is spread from human to human by females of the various Anopheles group of mosquitoes. Dengue fever has a worldwide distribution in tropical and subtropical areas. In addition to producing the classical fever with severe myalgia (breakbone fever), it can also cause a hemorrhagic fever. The causative agent, a group B arbovirus with four distinct serogroups, is virus- conveyed from case to case by the A aegypti mosquito. Colorado tick fever occurs mainly in mountainous areas of the United States within the range of its vector, D. andersoni. The highest incidence is in May and June. Several hundred cases are recorded annually, but it is likely that the actual incidence is much higher. Avoidance of tick bites is the principal control measure. Yellow fever, the prototypical viral hemorrhagic fever, is African in origin but has spread to and remains endemic in equatorial regions of Central and South America. The vector, A. aegypti, has also spread worldwide, but surprisingly, cases have not been reported in India and Southeast Asia. The illness varies in severity from a mild, nonspecific fever to a more severe condition with hemorrhagic, hepatic, and renal manifestations.

• Question 284:

  A 16-year-old girl presents because she has not begun to menstruate. Also, breast development and pubic hair have not developed. She is 59 in. (150 cm) tall and weighs 115 lbs (52 kg). On examination, her vital signs are normal. She has skin folds on the lateral sides of her neck. She has evidence of cubitus valgus. Breasts are Tanner stage 1 and the nipples appear to be spaced wider than average. Pubic hair is Tanner stage 1. The external genitalia are normal. The vagina is of normal depth and a small cervix is seen on speculum examination. The uterus is present but small. There are no adnexal masses. Which of the following is the treatment of choice for this patient?

  A. estrogen replacement therapy
  B. estrogen plus progestin therapy
  C. clomiphene
  D. Follistim (recombinant FSH)
  E. gonadectomy
  B. estrogen plus progestin therapy

  ---

  Explanation

  The streak gonads of women with gonadal dysgenesis will never secrete sex hormones. Combined estrogen plus progestin is the correct choice to stimulate pubertal development. Estrogen alone,in long term, increases the risk that these women will develop endometrial adenocarcinoma. Clomiphene and Follistim are fertility-promoting agents used to stimulate ovulation in anovulatory women who have ovarian follicles. Women with Turner syndrome have few or no follicles and oocytes. Gonadectomy is necessary only when a Y chromosome is present in a woman with gonadal dysgenesis.

• Question 285:

  When making recommendations to a state general assembly against routine premarital screening, the State Health Commissioner used the following data to arrive at his conclusions. The state had a young adult population of 100,000. Their actual prevalence of human immunodeficiency virus (HIV) infection was 1 per 1000. The best screening test available had a sensitivity of 98% and a specificity of 95%. How many people in this population would have screened false positive?

  A. 4995
  B. 98
  C. 2
  D. 100
  E. 5000
  A. 4995

  ---

  Explanation

  The following table was constructed using the data in the question. There would be 4995 FPs, 98 TPs, and 2 FNs.

  

• Question 286:

  An 11-year-old girl has her first menses. Both ovaries contain approximately how many oocytes?

  A. 7 million
  B. 1 million
  C. 500,000
  D. 50,000
  E. 5000
  C. 500,000

  ---

  Explanation

  The maximum number of oocytes is 67 million at approximately 20 gestational weeks. At birth, the number of oocytes has decreased to about 1 million, and the number at puberty is 300,000500,000. Women at menopause still have a small number of oocytes, a number insufficient to produce an amount of estrogen to prevent vasomotor symptoms. By simple mathematics, women lose approximately 1000 oocytes per menstrual cycle: one by ovulation and the remainder by follicular atresia.

• Question 287:

  A 22-year-old woman and her 24-year-old partner have been attempting to conceive for 12 months. They have sexual intercourse two to three times per week and use no contraception or coital lubricants. She has never been pregnant and her husband has fathered no pregnancies. She has no history to suggest damage to her Fallopian tubes and her menses occur at 28- to 31-day intervals.

  The statistic is fecundability. Fecundity is defined as the probability of having a liveborn child per ovulation. What is the fecundity of normally fertile couples?

  A. 5%
  B. 10%
  C. 20%
  D. 35%
  E. 50%
  B. 10%

  ---

  Explanation

  While the probability of conception per ovulation is approximately 20%, about 50% of all conceptions in humans end as a pregnancy loss. Of this percentage, 35% of pregnancies end so early that women never realize they conceived. The remaining 15% are recognized pregnancy losses, most in the first trimester. Stated otherwise, only 10% of women who conceive will have a liveborn child (50% of the 20% conception rate per ovulation). Fecundity in the future (probability of having a liveborn child) is not reduced after a single pregnancy loss.

• Question 288:

  A 37-year-old man and his wife seek help for their 5-year history of primary infertility. Her infertility investigation is normal. However, the husband has an ejaculate volume of 0.4 mL, and there are no sperm in the ejaculate. Aqualitative test for fructose in the semen is negative. Which of the following is the most likely diagnosis?

  A. germ cell aplasia
  B. bilateral occlusion of the vasa deferentia
  C. 17-hydroxylase deficiency
  D. congenital absence of the vasa deferentia
  E. Klinefelter syndrome
  D. congenital absence of the vasa deferentia

  ---

  Explanation

  The normal ejaculate volume is 25 mL, and the bulk of the ejaculate is from the seminal vesicles. The reduced ejaculate volume may be the result of an incomplete collection or may indicate absence of the seminal vesicles. Fructose is the reducing sugar produced by the seminal vesicles, and its absence establishes a diagnosis of congenital bilateral absence of the vasa deferentia and seminal vesicles. This explains the azoospermia (absence of sperm; aspermia is absence of an ejaculate). Men with germ cell aplasia have only Sertoli cells in their seminiferous tubules. Their ejaculate volumes are normal, and fructose is present. Likewise, men with occlusion of the vasa deferentia will be azoospermic but have a normal ejaculate volume containing fructose. Men with 17- hydroxylase deficiency will have hypertension, be sexually infantile, and have azoospermia, because the enzyme deficiency prevents the secretion of normal amounts of cortisol, androgens, and estrogen, but an increased secretion of mineralocorticoids. Men with Klinefelter syndrome have patent vasa deferentia and seminal vesicles; their ejaculate volumes will be normal and contain fructose.

• Question 289:

  A25-year-old man presents in the emergency department for a 2-week problem of worsening urinary hesitancy. He has had problems getting his urine stream started and has noted a decrease in the force of the stream. Now it seems to just "dribble out." He denies any pain or burning, any medical problems, and any exposure to sexually transmitted diseases. For approximately 1 month, he has been taking thioridazine, 200 mg bid, and benztropine, 2 mg qid, and "sometimes one or two benztropine" prn.Given the above information, which of the following is the most likely cause of this man's problem?

  Which of the following is a safer choice of medication for this man?

  A. amitriptyline
  B. risperidone
  C. chlorpromazine
  D. mesoridazine
  E. imipramine
  B. risperidone

  ---

  Explanation

  Given the temporal relationship in the start of two anticholinergic drugs and the onset of the urinary hesitancy in an otherwise healthy young male, it would be reasonable to conclude that he drugs are causing the problem. Certainly, a rapid assessment regarding the possibility of other causes (e.g., infection, trauma, stricture) is important. Careful, attentive listening for any hint of psychotic delusion involving urination is important to screen for. The manner in which the patient describes his symptoms is invaluable in facilitating diagnosis. Also remember that a real medical condition can be described in bizarre, distorted terms, making assessment more difficult and complicated. Drug-induced urinary hesitancy may be treated by discontinuing the causative medications. In addition, bethanechol, 1030 mg three to four times each day, may be administered. Bethanechol acts by stimulating the parasympathetic nervous system. The tone of the detrusor urinae muscle increases, producing a contraction strong enough to initiatemicturition and emptying of the bladder. Giving benztropine, an anticholinergic, would only heighten the problem. Unfortunately, some patients understand that benztropine is "for the side effect" of their antipsychotic medication but do not understand the difference between the extrapyramidal effect and the anticholinergic effects. Increased thioridazine would also increase the urinary problem. Calling in a urologist would be indicated if the initial treatment failed to work or if the emergency department physician were not able to "get beyond" an extremely distorted, disorganized presentation by the patient. If the bladder were extremely distended and the patient very uncomfortable, insertion of a urinary catheter would be a reasonable course of action. In the patient described, the bladder is not distended.

  Of the medications listed, risperidone is a reasonable and safe choice because its anticholinergic effects are low compared to the other drugs listed, and much lower than thioridazine. Chlorpromazine and mesoridazine have substantial anticholinergic effects. Amitriptyline and imipramine have substantial anticholinergic effects, and, in addition, they are tricyclic antidepressants, not antipsychotics.

• Question 290:

  A 44-year-old woman had a normal Pap smear 3 years ago. Her menstrual periods occur monthly and last 5 days. She has had intermenstrual and postcoital spotting intermittently for the past 6 months. The pelvic examination is normal.

  Which of the following is the most appropriate test to perform?

  A. an endometrial biopsy
  B. an endocervical curettage
  C. a conization of the cervix
  D. a Pap smear
  E. a hysteroscopy
  D. a Pap smear

  ---

  Explanation

  Postcoital spotting and intermenstrual spotting in a woman with cyclic menses is suggestive of a cervical abnormality, rather than an endometrial hormonal abnormality. In the absence of a visible lesion, a Pap smear that includes cells from both the ectocervix and endocervix is the preferred method of evaluation, especially when the woman has no history of cervical pathology or a normal Pap smear in the recent past. Endometrial biopsy and hysteroscopy assess the endometrium, not the cervix. A conization of the cervix should be reserved for women with documented cervical neoplasia when determination of the extent ofthe lesion is necessary. An endocervical curettage is usually reserved for women with unsatisfactory Pap smears and persistent abnormal bleeding.