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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 531:

  Which of the following risk factors has the strongest association with the development of malignant melanoma?

  A. dark skin and hair color with tendency to tan easily and not to burn easily
  B. personal history of sunburn, especially early in life
  C. pigmented lesion with asymmetric irregular borders, color variegation, and diameter 8 mm
  D. family history of non-melanoma skin cancer
  E. development of actinic keratosis
  C. pigmented lesion with asymmetric irregular borders, color variegation, and diameter 8 mm

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  Explanation

  History of excess sun exposure and sunburn early in life is associated with increased incidence of skin cancers, including melanoma, but the highest risk would be the development of a suspicious pigmented lesion. Clinicians can be guided by the "ABCD" rules: asymmetry, irregular borders, color variegation within the same lesion, and diameter >6 mm. Other risk factors for melanoma would include fair skin and hair with tendency to burn easily and a family history of melanoma. Actinic keratoses are premalignant lesions, but can develop into cutaneous squamous cell malignancies, not melanoma.

• Question 532:

  You are evaluating a journal article describing a test for the diagnosis of congestive heart failure (CHF). In the study described, 250 consecutive patients were given the test. Of the 250 subjects, 106 tested positive for CHF and 144 tested negative. All 250 subjects were then evaluated by expert cardiologists who were blinded to the results of the experimental test. These cardiologists determined that of the 106 persons who tested positive, 95 actually had CHF. Further, the cardiologists found that of the 144 who tested negative, 2 truly had CHF

  What is the positive predictive value (PPV) of this test for the diagnosis of CHF?

  A. 99%
  B. 93%
  C. 90%
  D. 85%
  E. 77%
  C. 90%

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  Explanation

  Explanations:

  Understanding the concepts of sensitivity, specificity, PPV, and NPV is crucial to interpreting diagnostic test results. Sensitivity is defined as the percentage of people who have a disease who test positive for that disease. Specificity is defined as the percentage of people who are free of a disease who test negative. These two concepts are considered characteristics of the specific test in question and are independent of the prevalence of the disease in the population. The PPVs and NPVs of a test are the test's clinical characteristics and these concepts are directly related to the prevalence of the disease in the population. The PPV is the percentage of people who have a positive test result who actually have the disease. Similarly, the NPV is the percentage of people who have a negative test result who don't have the disease.

  While the definitions may seem subtly different, the implications are significant. The usual way to calculate sensitivity, specificity, PPV, and NPV is with the table, using the following definitions

  

  The definitions of sensitivity, specificity, PPV, and NPV would then be:

  Sensitivity = a/(a + c) Specificity = d/(d + b) PPV = a/(a + b) NPV = d/(d + c) The specific information in this question comes from an article describing a study of B-type natriuretic peptide (BNP) for the diagnosis of CHF. The data presented show that 106 persons tested positive using the BNP test. After comparison with the "gold standard," in this case, a review by expert cardiologists, 95 of these 106 were determined to truly have CHF. Therefore, 11 of the 106 were false positives and 95 were true positives. Similarly, 144 persons tested negative using the BNP test. Of these, 142 were confirmed as true negatives and 2 were determined to be false negatives.

  Putting these numbers into a table reveals:

  

  The calculations then become:

  Sensitivity = a/(a + c) = 95/(95 + 2) = 98% Specificity = d/(d + b) = 142/(142 + 11) = 93% PPV = a/(a + b) = 95/(95 + 11) = 90% NPV = d/(d + c) = 142/(142 + 2) = 99%

• Question 533:

  Mr. Jones is a 34-year-old married businessman. He and his wife are both patients in your practice. As part of his annual physical, you screen for high-risk behaviors and he admits to receiving confidential treatment at a public health clinic for gonorrhea and genital herpes. He has not revealed this information to his wife even though they are planning to have a baby. He did not return for the results of HIV screening at the public health clinic. On physical examination, you note that he has cervical and axillary lymphadenopathy, oral thrush, and seborrheic dermatitis.

  What is the best step in his clinical management?

  A. Prescribe Mycelex troches.
  B. Schedule a lymph node biopsy.
  C. Prescribe Lotrisone (betamethasone/clotrimazole) cream.
  D. Repeat HIV serologic testing.
  E. Contact his wife for sexually transmitted disease (STD) screening.
  D. Repeat HIV serologic testing.

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  Explanation

  Although Mycelex troches would be appropriate in the management of his oral candidiasis and the Lotrisone would treat his seborrheic dermatitis, the patient has previously described risk factors for HIV infection and physical symptoms of immunodeficiency. Accurate knowledge of his HIV status is essential in the appropriate long-term management of this patient. In fact, his current physical examination suggests long-standing HIV infection. A lymph node biopsy is not warranted. His wife will eventually need screening for STDs since active STDs increase her risk of cotransmission of HIV. The patient's refusal to discuss his situation with his wife raises many controversial issues with no simple solution. There are multiple arguments which support the ethical guidelines for supporting patient confidentiality.

  These include:

  ?An appeal to consequences (potential patient discrimination secondary to health information; importance of trust) ?Appeal to virtue (physician fidelity) ?Respect (awareness and compassion for patient vulnerability) ?Do no harm (breach of medical information may lead to discrimination) Respect for patient autonomy incorporates the patient in the treatment process and is based on mutual trust. Referring Mr. Jones to another physician doesn't address the concerns involved in the care of Mrs. Jones. The Tarasoff case (1976) established the following precedent: Patient confidentiality must be upheld as part of the protected clinicianpatient relationship but the physician has a duty to warn specific, innocent third parties of potential harm threatened or posed by the patient. In fact, failure to warn by the physician may constitute negligence. This is not the law in all states. Some states interpret the standard as a strict duty to warn; other states permit physicians to warn affected third parties but not require it. If the physician unilaterally discloses the HIV status, it would represent a breach of confidentiality. However, their marital status may allow this disclosure. Even if the patient is adamant in his refusal, the physician needs to determine the reasons for his reticence. As his physician, you can provide additional information about HIV prevention and treatment. It would be highly unusual for Mr. Jones to ultimately refuse notification of his spouse once he has been urged to do so by his physician. The mechanism for how these complex issues are addressed has potential ramifications for his future trust of physicians, consent to HAART (highly active antiretroviral therapy) treatment, and medication compliance. If these barriers to disclosure cannot be addressed within the physician-patient relationship, the health department can provide a mechanism for contact testing. Although you could ask Mrs. Jones to come in for a physical examination, she might refuse to have STD tests performed, especially if she perceives herself to be at minimal risk. Ideally, this assessment should be performed prior to a pregnancy. If she is currently HIV negative, then protective measures against future infection can be introduced.

• Question 534:

  A70-year-old White woman has been faithful about taking 1200 mg of calcium, 400 IU of vitamin D supplements, and performing weight-bearing exercise on a daily basis. Her hip T score from her current DEXA scan has changed from -2.0 SDs to -2.55 SDs compared with last year's test.

  Which of the following statements is correct?

  A. With osteoporosis, serum calcium is low.
  B. With hyperparathyroidism, serum calcium is normal.
  C. With Paget disease, serum calcium is low.
  D. With renal failure, serum calcium is low.
  E. With osteomalacia, serum calcium is high.
  D. With renal failure, serum calcium is low.

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  Explanation

  This patient meets criteria for the diagnosis of osteoporosis, with a T score falling below -2.5 standard SD. AT score indicates the number of standard deviations below or above the average peak bone mass in young, healthy adults of the same gender. Bisphosphonate therapy has been shown to reduce vertebral and hip fracture risk in up to 50% of women with documented osteoporosis. GnRH therapy and discontinuation of her vitamin D therapy would worsen, not improve, this patient's bone density.

  Although testosterone may arrest further bone loss, the side effects of the medication are too great compared to any potential benefit.

  For women who have osteoporosis the serum calcium level is generally normal. In premenopausal osteoporosis, or more severe cases of bone loss/fractures, the presence of metabolic bone disease should be considered. In hyperparathyroidism the serum calcium is elevated. With renal failure, as with osteomalacia, serum calcium is low. The serum calcium level is normal, and the alkaline phosphatase level is elevated in patients with Paget disease. The use of tobacco, a family history of mother or maternal grandmother with hip fractures, postmenopausal state without estrogen replacement, vision problems, and a body mass index of less than 23 are all increased risks for fractures. Abody mass index of greater than 23 does not represent an increased risk for fracture.

• Question 535:

  A 25-year-old man presents to the ER with a 3-month history of intermittent pounding headaches, sweating, and palpitations. He denies any symptoms of depression or anxiety. On examination, he is a thin gentleman, BP 240/120, heart rate 110/minute, thyroid not enlarged. There is no prior history of hypertension.

  The most likely diagnosis is which of the following?

  A. carcinoid syndrome
  B. thyroid cancer
  C. pheochromocytoma
  D. aldosteronoma
  E. renal artery stenosis
  C. pheochromocytoma

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  Explanation

  The classic triad of pheochromocytoma is sweating, headache, and palpitations. When these are associated with hypertension, they have a sensitivity and specificity of >90% for the diagnosis. Paroxysms are not a component of aldosterone secreting tumors or renal artery stenosis. Hyperthyroidism and panic attacks would be in the differential diagnosis, but thyroid cancer is not associated with hypertension.

• Question 536:

  An 8-month-old boy is brought to the clinic by his mother because he has been lethargic, fussy, and not feeding well over the past several days. The mother has been working two jobs so the baby has been cared for by her boyfriend for the past month. She is very worried because he has not been smiling and vocalizing as much as he normally does and he has not been able to lift his head.

  What is the most common cause of injury in the first year of life?

  A. falls down stairs
  B. child abuse
  C. motor vehicle collisions
  D. dog bites
  E. other children
  B. child abuse

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  Explanation

  There are nearly 900,000 victims of child abuse in the United States each year. An inflicted injury is the most common cause of injury in the first year of life. As a child becomes more mobile, falls and motor vehicle accidents become increasingly more common. Other children are a very rare cause of serious injury in childhood. (Department of Health and Human Services, 2002) Brain injury that results from violent shaking of the infant is known as Shaken baby syndrome. These infants can present with seizures, a bulging fontanelle, or irritability presenting a clinical picture similar to that of a septic infant. Intracranial injury is evident on CT or MRI and with a funduscopic examination revealing retinal hemorrhages. Accidental bruises are usually found over bony areas such as shins, knees, elbows, and forehead. Linear fractures of the skull can result from low-energy blunt trauma over a wide surface area of the skull. Nursemaid's elbow is a common condition in young children and generally affects children under 5. It occurs when a child is pulled up too hard by the hand or wrist resulting a in a partial dislocation of the elbow.

• Question 537:

  A 50-year-old male presents to your office after reading an article on the Internet stating that a recent study showed that the drug finasteride can prevent prostate cancer. He asks you to prescribe this medication for him. You review the article and find the following information: a randomizedcontrolled trial of men over the age of 55 with normal prostate-specific antigen (PSA) readings was performed comparing finasteride and a placebo. At the end of the study, 18% of the men in the finasteride group and 24% of the men in the placebo group had developed prostate cancer.

  Further review of the article reveals that 6.4% of the men in the finasteride group and 5.1% in the placebo group developed high-grade prostate cancers. How many men need to take finasteride in order to have one excess case of high-grade prostate cancer (number needed to harm [NNH])?

  A. 1.3
  B. 12
  C. 37
  D. 77
  E. 94
  D. 77

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  Explanation

  Explanations:

  The NNT is calculated by first determining the ARR for a specific outcome between two groups in a study. The ARR, or risk difference, is calculated by subtracting the percentage of subjects who develop an The outcome in the treatment group from the percentage who develop the outcome in the control group. outcome considered is the development of prostate cancer. This occurred in 24% of the control group and 18% of the finasteride group. The ARR is calculated as 24% - 18% = 6% or 0.06. The NNT is calculated as: NNT = 1/ARR. In this example, the NNT = 1/0.06 = 16.67, approximately 17. This suggests that for every 17 men who took finasteride there was one fewer case of prostate cancer. The NNH is calculated in exactly the same manner as the NNT. The only difference is that the outcome is adverse. In this study, highgrade prostate cancers occurred more often in the finasteride group than the placebo group; 6.4% of men who took finasteride and 5.1% who took a placebo developed high-grade prostate cancer. The risk difference, in this case an absolute risk increase, is 6.4% - 5.1% = 1.3% or 0.013.

  The NNH = 1/absolute risk increase = 1/0.013 = 77

• Question 538:

  A 42-year-old woman with hyperlipidemia, hypertension, and hypothyroidism presents to your office for a routine follow-up visit. Her blood pressure is well controlled with hydrochlorothiazide. She has been on a stable dose of levothyroxine for 8 years and measurement of her TSH today is within normal limits. However, her LDL cholesterol level remains elevated despite taking a statin for the past 9 months and complying with lifestyle modifications. You decide that the addition of a low dose of cholestyramine would provide her with additional benefit. How would you advise the patient before beginning this therapy?

  A. She should take other medications at least 1 hour before or 4 hours after cholestyramine.
  B. She should take a multivitamin tablet daily.
  C. She should ingest the cholestyramine in its dry form.
  D. She may mix the cholestyramine with water, juices, or carbonated beverages.
  E. She should discontinue the cholestyramine immediately if she experiences steatorrhea.
  A. She should take other medications at least 1 hour before or 4 hours after cholestyramine.

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  Explanation

  Cholestyramine is a bile acid sequestrant which binds bile acids and similar steroids in the intestine, thereby reducing concentrations of LDLs in the circulation. Orally administered drugs may also bind to cholestyramine, however, impairing their efficacy by impairing absorption in the gut. This problem can be alleviated by administering other oral medications at least 1 hour before or 4 hours after cholestyramine. Examples of compounds which may be bound by cholestyramine include warfarin, digoxin, glipizide, phenytoin, methyldopa, thiazide diuretics, niacin, and statins. Fat-soluble vitamins (A, D, E, and K) may also bind to cholestyramine. Cholestyramine powder should never be administered in its dry form due to the risk of aspiration. It should be combined with water, pureed- consistency food, or a noncarbonated beverage. Use of carbonated liquids as a solvent may exacerbate the common side effects of heartburn and indigestion. Fat-soluble vitamins (A, D, E, and K) may also bind to cholestyramine; if steatorrhea develops, with associated impairment of fatsoluble vitamins, vitamin supplementation is recommended.

• Question 539:

  A28-year-old woman presents for evaluation of primary infertility. She has had fewer than four periods per year since menarche at age 14, facial hirsutism, acne, and weight gain. On examination, she has a BP 150/100. Her body mass index (BMI) is 40. Acanthosis nigricans is noted along the posterior surface of her neck. How would you counsel this patient?

  A. The primary treatment for this problem is with medications.
  B. Weight loss is key to her management.
  C. Her hypertension would be best treated with a thiazide diuretic.
  D. Regardless of her lipid panel result, she should be on a statin.
  E. Her infertility is due to lack of estrogen production.
  B. Weight loss is key to her management.

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  Explanation

  The patient has the typical features of PCOS associated with insulin resistance and the metabolic syndrome. The presence of hyperandrogenism and oligomenorrhea, without other known causes (such as congenital adrenal hyperplasia), makes the diagnosis of PCOS. The hirsutism and acne are the result of the hyperandrogenism associated with PCOS. Thyroid disorders and hyperprolactinemia can contribute to menstrual disturbances but would not be expected to cause the signs of androgen excess or

  A. nigricans. A cosyntropin stimulation test would be used for the diagnosis of adrenal insufficiency. Growth hormone levels may be elevated in acromegaly or in some pituitary tumors. Women with PCOS have a high risk of glucose intolerance, diabetes, dyslipidemia, and hypertension. Individuals with insulin resistance syndromes typically exhibit hypertriglyceridemia with low HDLlevels. The key to management of PCOS is weight loss. Even modest weight loss (1020 lbs) can result in significant improvement

  in metabolic and physiologic parameters, such as blood pressure and insulin resistance, and improved fertility

• Question 540:

  A 48-year-old woman with metastatic breast cancer presents to the Emergency Center complaining of a 4- day history of nausea, anorexia, and generalized weakness. Her husband reports that she has been more somnolent, sleeping 1214 hours per day, and at times she seems confused. CT scan of the brain reveals no abnormalities. Initial laboratory evaluation reveals a normal CBC, but her BUN is elevated at 32 mg/dL with a slight elevation of serum creatinine above her baseline. Her serum calcium is elevated at 15 mg/dL.

  What is the most likely cause of her hypercalcemia?

  A. widespread osteolytic metastases
  B. ectopic production of a parathyroid hormone-related protein
  C. excessive administration of oral calcium and Vitamin D supplementation to prevent osteoporosis
  D. undiagnosed primary hyperparathyroidism
  E. side effect of medications such as thiazide diuretics
  B. ectopic production of a parathyroid hormone-related protein

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  Explanation

  The patient is hypercalcemic and has laboratory features suggesting dehydration, as do most patients with symptomatic hypercalcemia. Initial management would include saline rehydration, which replaces volume deficits, dilutes the elevated serum calcium, and promotes urinary calcium excretion. The addition of loop diuretics such as furosemide can also increase calciuresis, but should only be added after the patient has had adequate volume repletion. Administration of bisphosphanates, such as pamidronate or zoledronate, provide more powerful reduction of serum calcium by inhibiting bone resorption and liberation of calcium. Their effects may last for several weeks, but their onset of action does not occur for 12 days. Subcutaneous calcitonin can provide a faster onset of action to inhibit bone resorption within a few hours, but patients develop tachyphylaxis and become unresponsive to the drug effect within 2448 hours. Most cancer patients with hypercalcemia develop this problem as a paraneoplastic phenomenon, due to the production of a parathyroid hormone-related protein (PTHrP).

  This problem, called humoral hypercalcemia of malignancy (HHM), is very common, affecting 510% of all cancer patients. The diagnosis is usually straightforward, as there is a readilyavailable laboratory assay for PTHrP. Other cancer patients develop HHM due to the production of an enzyme that converts 25- hydroxyvitamin D to the more active 1,25- hydroxyvitamin D, similar to the hypercalcemia seen in patients with granulomatous diseases. Severe hypercalcemia solely due to the presence of osteolytic metastases is much less common. Hyperparathyroidism and medications such as thiazide diuretics can also cause elevations of serum calcium, but usually not to the severe levels seen in HHM.