USMLE USMLE-STEP-3 Online Practice Questions and Exam Preparation

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 651:

  A27-year-old nulligravid single White female presents to your office for an annual examination. In taking her history, you learn that her mother died of ovarian cancer at the age of 63. There is no other family history ofbreast or ovarian cancer. The patient asks you to tell her what she can do to reduce her own ovarian cancer risk. What is the most effective strategy appropriate for this patient to reduce her risk?

  A. bilateral laparoscopic salpingooophorectomy
  B. daily aspirin use
  C. oral contraceptive therapy
  D. bilateral tubal ligation
  E. avoidance of breast-feeding following pregnancy
  C. oral contraceptive therapy

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  Explanation

  A meta-analysis of 20 studies published from 1970 to 1991 demonstrated a significant reduction in the risk of ovarian epithelial carcinoma with the use of oral contraceptives. The risk of ovarian cancer decreased with increasing duration of oral contraceptive use: a 1012% decrease in lifetime risk was noted with 1 year of use, a 50% decrease in lifetime risk noted with 5 years of use, and an 80% decrease in lifetime risk associated with 10 years of use. Oral contraceptive therapy has consistently demonstrated in epidemiologic studies the ability to decrease a woman's lifetime risk for the development of ovarian cancer. It is the most effective means of primary prevention in women at high risk for the development of ovarian cancer, short of physically removing the ovaries themselves. Both hysterectomy and bilateral tubal ligation have been associated with a 30% decrease in the lifetime risk for the development of ovarian cancer. However, in women yet to complete their childbearing neither is a realistic option.

  Breast-feeding and increasing parity have been shown to decrease a woman's lifetime risk for the development of ovarian cancer. There are some data to suggest that anti- inflammatory medications (aspirin, NSAID) may decrease the risk of ovarian cancer, but this has yet to be substantiated in epidemiologic studies.

• Question 652:

  A 14-year-old boy is brought to the emergency department for evaluation of fever and headache. The mother relates that her son has had a worsening headache for 56 days. She says that she took him to a walk-in clinic, and he was put on amoxicillin for a sinus infection. His headaches have been getting worse and that he is now having fevers as high as 103.6 . The mother says that he normally is very active and that he currently has a summer job at a local park clearing out underbrush. Since he has become ill, he has had such a decrease in energy that he cannot go to work. He has had a decrease in his appetite and has been sleeping more. He denies any sore throat, abdominal pain, chest pain, dysuria, vomiting, or diarrhea. On examination, he is an uncomfortable young man whose vital signs are: temp 101.9, RR 26, HR 124, and BP 79/56. is head, ear, eye, nose, and throat examination reveals normal TMs, a mildly erythematous hypopharynx, and some shotty cervical lymphadenopathy. His lungs are clear. His cardiac examination is normal. His liver edge is palpable just below the right costal margin and is mildly tender. His spleen is not palpable. His skin examination is normal with the exception of scattered petechiae around his ankles and wrists. A CBC reveals WBC 13,000 with 65% segs and 22% lymphs, hematocrit of 35, and platelet count of 95,000. His electrolytes reveal a Na 125, K 5.1, Cl 102, and bicarbonate 21. His BUN and Cr are normal.

  The best treatment course would include which of the following?

  A. continue amoxicillin only
  B. begin oral doxycycline
  C. add acyclovir to the amoxicillin
  D. begin oral corticosteroids
  E. stop all antimicrobials
  B. begin oral doxycycline

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  Explanation

  Typical symptoms include a summertime fever, headache, petechial rash, thrombocytopenia, and hyponatremia. This may be mistaken for a systemic enteroviral infection, or enteroviral encephalitis, but the presence of thrombocytopenia and hyponatremia would exclude this diagnosis. Still disease (systemic- onset JRA) would have an elevation of acute-phase reactants, including the WBC and platelet count. Fourteen years old is an unlikely age for Kawasaki disease, and the acute phase reactants would likewise also be elevated.

  RMSF is a very serious infectious illness. Appropriate antimicrobial therapy, usually doxycycline, needs to be started as soon as the diagnosis is seriously considered, as this can prevent some of the more severe sequelae. The use of systemic corticosteroids has no place in the management of RMSF. Confirmation of RMSF is serologic. Rising IgG titers or the presence of IgM titers to R. rickettsii is a confirmation of RMSF

• Question 653:

  Routine screening is advocated by numerous authorities for many different types of cancer. These screening programs have resulted in various degrees of success in terms of reduction in mortality. Cytologic screening for cancer of which of the following organs has successfully produced a marked reduction in mortality?

  A. breast
  B. lung
  C. uterine cervix
  D. pancreas
  E. prostate
  C. uterine cervix

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  Explanation

  Mortality from cervical carcinoma has been considerably falling throughout the years and that is secondary to multiple factors, such as cytologic screenings (pap smears), early detection, and treatment of dysplasia.

• Question 654:

  A 45-year-old male has received intravenous contrast dye prior to CT scan of the abdomen. Twenty minutes later the patient reports severe pruritus. He denies respiratory distress, syncope, or palpitations. His blood pressure is 98/54, pulse is 90, and respiratory rate is 22. On physical examination, he has widespread urticaria. His lungs are clear to auscultation. The next appropriate step would be which of the following This intervention works well in cases such as this due to activity directed toward which of these receptors?

  A. dopaminergic receptors
  B. muscarinic receptors
  C. nicotinic receptors
  D. adrenergic receptors
  E. N-methyl D-aspartate (NMDA) receptors
  D. adrenergic receptors

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  Explanation

  Anaphylaxis is an acute multisystem allergic reaction to a particular antigen in a sensitized patient. The reaction may be mild or severe. Clinical manifestations may include urticaria and angioedema; laryngeal edema with dyspnea; bronchospasm; tachycardia and hypotension; and vomiting and diarrhea. The correct initial step in the treatment of mild anaphylaxis is the administration of 0.30.5 mL of 1:1000 epinephrine subcutaneously. (Kaspar et al., 2005, pp. 19491950) Epinephrine is the drug of choice for treating severe anaphylactic shock because it is active at both alpha- and beta- adrenergic receptors. The alpha- adrenergic effects constrict the smaller arterioles and precapillary sphincters, thereby markedly reducing cutaneous blood flow. Veins and large arteries also respond to epinephrine. The beta-adrenergic effects of epinephrine cause relaxation of the bronchial smooth muscle and induce a powerful bronchodilation, which is most evident when the bronchial muscle is contracted, as in anaphylactic shock

• Question 655:

  A43-year-old Black female (gravida 3, para 3) with a previous tubal ligation, presents to your office complaining of increasing menorrhagia, dysmenorrhea, and fatigue over the past 6 months. On examination, her vital signs are normal, and on abdominal examination you palpate a firm, mobile mass just below the umbilicus. On pelvic examination, there is a moderate amount of old blood coming from the cervical os. A urine pregnancy test is negative, her last pap smear was normal and her spun HCT today is 28%.

  Which pharmacologic agent would potentially result in an improvement in her HCT and help to decrease uterine size?

  A. oral contraceptive pills (OCPs)
  B. medroxyprogesterone
  C. nonsteroidal anti-inflammatory agents
  D. narcotics
  E. GnRH agonists
  E. GnRH agonists

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  Explanation

  Pelvic ultrasound is the least invasive and most cost-effective test to diagnose uterine fibroids. MRI is useful but not always readily available and much more expensive. Plain radiographs would not be helpful, and office laparoscopy is impractical and potentially dangerous given the presumed size of her uterus. A hysterosalpingogram would only note filling defects within the uterine cavity and miss intramural or subserosal fibroids.

  GnRH agonists have been used widely for preoperative treatment of uterine fibroids. They work by inducing amenorrhea, which improves hematologic parameters and decreases uterine volume. Although nonsteroidal anti-inflammatory drugs (NSAIDs) may help decrease bleeding for some patients with fibroids, they have not been reliably shown to decrease fibroid size. The other agents (OCPs, progesterone, and narcotics) do not have these effects and generally are not effective in treating dysfunctional uterine bleeding caused by anatomic lesions such as fibroids

• Question 656:

  Polyarteritis nodosa (PAN) typically involves which of the following?

  A. large elastic arteries
  B. small- or medium-sized muscular arteries
  C. arterioles
  D. capillaries
  E. venules
  B. small- or medium-sized muscular arteries

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  Explanation

  PAN typically involves small- to mediumsized muscular arteries. In contrast, large arteries and the aorta are involved in Takayasu arteritis. Small arteries and arterioles are involved in a number of other diseases, including systemic lupus erythematosus. Active lesions in PAN demonstrate a neutrophilic infiltration of the involved vessel wall with thrombosis and segmental, fibrinoid necrosis. Intermittent healing produces fibrosis of the arterial wall and intimal thickening, which may lead to obstruction and infarction. Aneurysmal dilations may arise as a result of asymmetrical involvement. Although the lesions in PAN resemble other immunemediated vascular lesions, the exact etiology of the disorder has not been elucidated. PAN generally affects middle-aged men and has a poor prognosis, although steroids may be beneficial.

• Question 657:

  A meta-analysis of randomized-controlled trials was published comparing two methods of managing postterm pregnancies. The question studied was whether the routine induction of labor at 41 weeks' gestation would result in improved maternal or fetal outcomes compared with expectant management. The authors reported that the odds ratio for caesarian delivery rate in the induction group compared to the expectant management group was 0.88 with a 95% confidence interval (CI) of 0.780.99. A second outcome studied was perinatal mortality. For this outcome, the odds ratio for the induction group compared to the expectant management group was 0.41 with a 95% CI of 0.141.18.

  Which of the following statements is true?

  A. There was a statistically significant reduction in the number of caesarian deliveries in the induction group compared to the expectant management group.
  B. There was a statistically significant reduction in perinatal mortality in the induction group.
  C. There was no statistically significant difference for either outcome.
  D. There was a statistically significant increase in the number of caesarian deliveries in the induction group compared to the expectant management group.
  E. There was a statistically significant decrease in both the number of caesarian deliveries and perinatal mortality in the induction group.
  A. There was a statistically significant reduction in the number of caesarian deliveries in the induction group compared to the expectant management group.

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  Explanation

  Explanations:

  The odds ratio is a frequently published statistic. The odds of an event occurring are the number of times an event occurred divided by the number of times that it did not. In medical studies, it is calculated by dividing the number of subjects who achieved a certain outcome by the number of subjects who did not. An odds ratio is calculated by dividing the odds of an event in one group by the odds of the same event in another group. This is frequently an experimental group and a control group. In the study presented in this question, the "experimental" group is the induction of labor group and the control is the expectant management group. An odds ratio of less than one means that the outcome in question occurred less often in the experimental group than in the control group. Conversely, an odds ratio of greater than one reveals that the outcome occurred more often in the experimental group than the control group. In the study presented, the odds ratios for both the outcomes of caesarian delivery and perinatal mortality are less than one, suggesting that these outcomes occurred less often in the group of women treated with induction of labor at 41 weeks' gestation compared to those treated with expectant management. A CI is a range within which the "true" result is likely to be found. A95% CI states that there is a 95% probability that the true answer exists within these bounds.

  For statistics, such as odds ratios or relative risks, a 95% CI that includes the number 1 within its bounds is considered not statistically significant. This is because an odds ratio of 1 means that there is no difference in the odds of an event occurring in either group. For the outcome of caesarian delivery, the odds ratio is 0.88 with a 95% CI that does not include 1. Therefore, one can say that there is a statistically significant reduction in the number of caesarian deliveries in the induction group compared to the expectant management group. For the outcome of perinatal mortality, the odds ratio is 0.41 but the 95% CI extends up to 1.18. This result cannot be considered statistically significant.

• Question 658:

  A 48-year-old woman complaining of dysuria is diagnosed with a UTI by urinalysis. Urine culture and sensitivities reveal that the causative organism belongs to the genus Klebsiella and is resistant to multiple antibiotics. Based upon the results available, you decide to begin therapy with gentamicin.

  Which of the following would lead to the classification of this patient's infection as "complicated?"

  A. a history of recurrent UTIs
  B. a diagnosis of type II DM
  C. the patient's gender
  D. a history of undergoing a laparoscopic appendectomy 1 month ago
  E. a postvoid residual volume of 25 cc
  B. a diagnosis of type II DM

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  Explanation

  Aminoglycosides such as gentamicin accumulate in the proximal tubular cells of the kidney, resulting in a defect in renal concentrating ability and reduced glomerular filtration after several days. This renal impairment is almost always reversible. Of all the aminoglycosides, gentamicin and tobramycin are the most nephrotoxic. Aminoglycosides may also cause ototoxicity in the form of irreversible auditory or vestibular damage. There is a direct relationship between aminoglycoside dosage and the risk for development of ototoxicity, so doses should be adjusted according to a patient's baseline renal function. Complicated UTIs involve metabolic or hormonal abnormalities such as those seen in M or during pregnancy; the presence of foreign bodies such as calculi, tumors, or catheters; the presence of strictures causing turbulent urine flow or vesicoureteral reflux; incomplete voiding such as that seen in neurogenic bladder, prostate hyperplasia or cancer; and, the presence of unusual infecting microorganisms.

  A history of recurrent UTI does not in itself lead to the classification of subsequent infections as complicated. Due to anatomic differences in urethral length between males and females, any UTI in a male is considered complicated. A history of recent surgery does not correlate with development of a complicated UTI unless the surgical procedure resulted in the creation of some anatomic abnormality which increased the risk of infection; examples of such abnormalities include adhesions or strictures.

  Apostvoid residual volume greater than 50100 mL suggests abnormal bladder emptying, which would predispose an individual to development of UTIs.

• Question 659:

  A22-year-old male presents to an acute care clinic in order to have two genital lesions evaluated. He first noticed the lesions about 2 weeks ago, but delayed seeking medical care because he believed they were harmless due to the lack of any discomfort. He states that he does engage in unprotected sexual intercourse, with the most recent time being 1 month ago. On examination, the glans penis features two distinct nontender papules with elevated edges surrounding ulcerated craters. They each measure 1 cm in diameter. There is also nontender bilateral inguinal lymphadenopathy.

  The drug of choice for treating this patient works by which of the following mechanisms?

  A. interfering with protein synthesis at the ribosome
  B. attaching to sterols in cell membranes
  C. inhibiting bacterial cell wall synthesis
  D. inhibiting the transport of amino acids into bacteria
  E. inhibiting dihydrofolate reductase
  C. inhibiting bacterial cell wall synthesis

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  Explanation

  This patient's presentation is consistent with primary syphilis. Primary syphilis manifests itself usually in the form of solitary or multiple raised, firm papules which eventually erode to form ulcerative craters with raised, indurated margins surrounding the centralized ulcer. These lesions, called chancres, most commonly involve the glans penis in males and the vulva or cervix in females, although they may appear rarely in other areas. Syphilis is caused by the spirochete, T. pallidum, which can be visualized by darkfield microscopy, by silver stain, or by fluorescent antibody microscopy. There is an incubation period of approximately 3 weeks separating the time of initial exposure to T. pallidum and the time of chancre formation. Syphilis is characterized by the presence of latent stages in which there are no signs of clinical disease present. Penicillin is the drug of choice for the treatment of syphilis. In addition to treating patients with diagnosed syphilis, it is recommended that treatment also be administered to all sexual contacts of the past 90 days. It has been demonstrated that up to 30% of asymptomatic sexual contacts of patients with infectious lesions within the past 30 days go on to develop syphilis if left untreated. If left untreated, patients may ultimately develop tertiary syphilis characterized by significant destructive neurologic and cardiovascular symptoms. The mortality rate for untreated tertiary syphilis is approximately 20%.

  Cephalosporins and penicillin antibiotics act by interfering with the late stages of bacterial cell wall synthesis, although the precise biochemical reactions are not entirely understood. Peptidoglycan provides mechanical stability to the cell wall because of its high degree of cross-linking with alternating amino pyranoside sugar residues (N-acetylglucosamine and N-acetylmuramic acid). The completion of the cross- linking occurs by the action of the enzyme transpeptidase. This transpeptidase reaction, in which the terminal glycine residue of the pentaglycine bridge is joined to the fourth residue of the pentapeptide (D- alanine) thereby releasing the fifth residue (D-alanine), is inhibited by beta- lactams.

• Question 660:

  A term infant male is born after an uncomplicated vaginal delivery. The mother's prenatal labs were negative with the exception of being GBS positive at 36 weeks' gestation. The mother received two doses of ampicillin prior to delivery and did not have a fever. The infant had APGAR scores of 9 at 1 minute and 9 at 5 minutes. The infant was brought to the newborn nursery and appears well

  The father tells you that he has hemophilia. His wife neither has hemophilia nor is a carrier.

  What does this mean for the baby?

  A. The baby has a 50% chance of having hemophilia.
  B. The baby neither has hemophilia nor is a carrier of the hemophilia gene.
  C. The baby is a carrier of the hemophilia gene but does not have the disease.
  D. The baby has a 25% chance of being a carrier for hemophilia.
  E. The baby has a 50% chance of being a carrier for hemophilia.
  B. The baby neither has hemophilia nor is a carrier of the hemophilia gene.

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  Explanation

  The most common bacterial infection in the newborn period is GBS. GBS is commonly cultured in the adult vaginal tract, and its vertical transmission can be interrupted with maternal antimicrobial treatment prior to delivery of the infant. Mothers are commonly treated in labor with penicillin, ampicillin, clindamycin, or azithromycin in an attempt to interrupt transmission to the infant while passing through the birth canal. If antimicrobial prophylaxis is initiated greater than 4 hours prior to delivery, the rate of early- onset GBS disease is dramatically decreased. The current recommendation for term infants of GBS-positive women who have received antibiotics in labor (at least two doses or =4 hours prior to delivery) is observation without testing or antibiotics. (American Academy of Pediatrics, 2003, pp. 584591) Classic hemophilia is an X-linked recessive bleeding diathesis. Hemophilia is inherited on the maternal lineage from carrier (or affected) mothers. This infant, being a male, would receive his X chromosome from his mother. He is, therefore, not at risk for having hemophilia. Further, being an X-linked trait, there cannot be a male "carrier" state.