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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 681:

  A 59-year-old White male with a 40 pack-year history of smoking presents to your clinic complaining of three prior episodes of a "shade passing over his left eye" over the last 2 months. He reports that last week he experienced some weakness in his right arm, which resolved after 5 minutes. Appropriate management and counseling for this patient includes which of the following?

  A. Initial management of this patient should include bilateral cerebral vessel duplex ultrasonography.
  B. Explanation to him that he has had a stroke and will be referred to a neurologist for management.
  C. The most common cause of strokes in these patients is related to decreased blood flow.
  D. Presence of a carotid bruit confirms the diagnosis and may lead to operative intervention without the need for imaging studies.
  E. The presence of a 50% stenosis in the right carotid artery should lead to bilateral surgical repair.
  A. Initial management of this patient should include bilateral cerebral vessel duplex ultrasonography.

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  Explanation

  This patient is experiencing multiple transient ischemic attacks (TIAs) associated with carotid artery disease. TIAs last only a few minutes, while RINDs (reversible ischemic neurologic deficit) typically resolve after 24 hours, and strokes result in long-term deficit. The symptoms are typically related to embolic events rather than reduced blood flow. The finding of carotid bruit on examination is more sensitive for coronary artery disease than it is for carotid disease. The initial workup for these patients should be bilateral carotid duplex ultrasound. Operative repair is indicated for asymptomatic patients with >60% stenosis as well as symptomatic patients.

• Question 682:

  A 49-year-old male presents with crushing substernal pain and rules out for a myocardial infarction. He is noted to have subcutaneous emphysema of the chest and neck and precordial crackles that correlate to his heartbeat but not his respirations.

  Which of the following is the most likely diagnosis?

  A. spontaneous pneumothorax
  B. esophageal perforation
  C. pericarditis
  D. pneumopericardium
  E. pulmonary embolus
  B. esophageal perforation

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  Explanation

  "Hamman's crunch" is precordial crackles heard on auscultation that correlate with heart sounds in the setting of mediastinal emphysema and is suggestive of esophageal perforation. When present along with subcutaneous emphysema of the chest and neck, pneumomediastinum from an esophageal perforation is the most likely diagnosis. The most common cause of esophageal perforation is iatrogenic, but it may be spontaneous (Boerhaave's syndrome) or secondary to a malignancy or stricture. Diagnosis is often made after clinical suspicion by endoscopy or a swallow study with water- soluble contrast. If diagnosed early (within 24 hours), a primary repair is the first approach to treatment. Closure is dependent on the amount of infected or necrotic tissue, tension on the anastomosis, etiology of the perforation, and the ability to adequately drain the contaminated areas. Late perforations may be complicated in their management, requiring several procedures or diversion to provide for adequate healing.

• Question 683:

  A 60-year-old man with a history of severe chronic obstructive pulmonary disease (COPD), which is steroid dependent, is admitted to the ICU with pulmonary infiltrates and a sepsis syndrome. His hospital course is complicated by acute renal insufficiency and respiratory failure. Therapy includes glucocorticoids and dopamine. He has no history of thyroid disease. Several weeks into his hospital course, the following laboratory studies are performed:

  Based on these laboratory studies, which of the following is the most appropriate next step?

  

  A. initiate levothyroxine therapy
  B. discontinue glucocorticoid therapy
  C. initiate methimazole therapy
  D. order MRI of the pituitary
  E. supportive treatment only
  E. supportive treatment only

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  Explanation

  The patient exhibits the typical features of the nonthyroidal illness syndrome. The total thyroxine level is low, but TBG is also low (based on the elevated T3 resin uptake), so that the free thyroid index is still in the normal range. The low TBG is related to the patient's nutritional deficiency. The low T3 and TSH levels are related to his illness and the use of both glucocorticoids and dopamine, which decrease TSH. The reverse T3 level is high because of the blockade of T4 to T3 conversion caused by the illness.

  This finding excludes hypopituitarism as an underlying cause. There is no specific therapy for this problem other than treating the underlying illness.

• Question 684:

  A 42-year-old man presents to your clinic with a 1-week history of pain and inflammation involving his right first metatarsophalangeal (MTP) joint. He describes the pain as sudden in onset and worse at night. He denies experiencing any fever or traumatic injury to the joint and states that he has never had this type of pain before. He denies any chronic medical conditions, any prior surgery, and any current medication use. Besides an erythematous and exquisitely tender right first MTP joint, the remainder of his physical examination is unremarkable.

  What is a potential long-term complication of this patient's condition?

  A. CHF
  B. nephrolithiasis
  C. anemia of chronic disease
  D. recurrent urinary tract infection (UTI)
  E. rheumatoid arthritis (RA)
  B. nephrolithiasis

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  Explanation

  This patient's presentation is consistent with gout. Aspiration of his first MTP joint is likely to reveal the presence of needle-shaped, negatively birefringent crystals. Rhomboid-shaped, positively birefringent crystals are characteristic of calcium pyrophosphate deposition disease, or pseudogout, with the knee being the joint most commonly affected. Nonbirefringent crystals are found in hydroxyapatite crystal deposition disease. The synovial fluid from joints affected by gout typically show evidence of inflammation in the form of leukocytosis with a predominance of polymorphonuclear neutrophils. The presence of bacteria in synovial fluid is characteristic of infection rather than gout, although gout and infectious arthritis may coexist. (Cecil Textbook of Medicine, pp. 17031708) Acute gouty arthritis usually presents in a monoarticular or oligoarticular distribution, with the first MTP joint most commonly affected. The diagnostic gold standard is detection of urate crystals within the synovial fluid of affected joints.

  It most commonly affects adult men with a peak incidence in the fifth decade of life. While patients with gout typically also have hyperuricemia, only a small fraction of the people with hyperuricemia actually have or will develop gout.

  Tophi are primarily seen in patients with long-standing hyperuricemia and is considered a finding of chronic gouty arthritis. As the disease progresses, acute attacks become more frequent and last longer if left untreated. Indomethacin inhibits the prostaglandin synthesis that facilitates the inflammation of acute gout and inhibits the phagocytosis of urate crystals by leukocytes. This inhibits the cell lysis and release of cytotoxic factors that initiate the inflammatory cascade. Allopurinol (an inhibitor of urate synthesis) and probenecid and sulfinpyrazone (promoters of urate excretion) are useful for preventing gout but are not effective during an acute gout attack. Aspirin is inappropriate in the treatment of gout since it can inhibit urate elimination and, therefore, increase hyperuricemia.

• Question 685:

  A mobile mass is found on rectal examination in a 77-year-old male with complaints of blood in his stool. On workup, he is found to have a stage I (Dukes' A), well-differentiated adenocarcinoma. The most appropriate intervention is which of the following?

  A. transanal excision
  B. abdominal perineal resection
  C. low anterior resection
  D. placement of endorectal wallstent
  E. neoadjuvant chemotherapy followed by transanal resection
  A. transanal excision

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  Explanation

  Local treatment of rectal cancer is the treatment of choice in selected individuals with low-lying rectal cancers. The lesion must be mobile, nonulcerated, within 10 cm of the anal verge, less than 3 cm in diameter, less that onefourth the circumference of the rectal wall, and stage T1 or T2 on endorectal ultrasound. Transanal excision is the most straightforward technique of local treatment. It entails full thickness excision of the lesion into the perirectal fat with adequate margins. For early lesions into the submucosa only (T1), no adjuvant therapy is required unless poor prognostic features are present on final pathology (poorly differentiated or lymphatic/vascular invasion). If the lesion penetrates the muscular wall (T2), adjuvant radiation therapy with or without chemotherapy is indicated following surgical removal.

  Overall, the disease free survival rate is 80%.

• Question 686:

  A32-year-old female presents for her first pap smear in more than 10 years. She has a history of heavy alcohol use and IV drug use and has performed sexual acts for drugs on numerous occasions. Testing performed today reveals her to have chlamydia cervicitis and trichomonas vaginalis and to be seropositive for hepatitis B and hepatitis C. HIV testing is negative. Her pap smear subsequently returns with carcinoma in-situ of the cervix.

  Infection with which of the following agents is most likely to have resulted in her cancer?

  A. human papillomavirus type 16
  B. hepatitis C virus
  C. hepatitis B virus
  D. Chlamydia trachomatis
  E. human papillomavirus type 11
  A. human papillomavirus type 16

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  Explanation

  Human papillomavirus has been associated with the development of multiple squamous cell malignancies, including cervical cancer (HPV types 16, 18, 31, 45, and 5153), as well as anal, penile, and vulvar cancers. Recent evidence has also linked some oropharyngeal squamous cell cancers to HPV infection as well. The risk for HPV-associated cancer is increased in patients with HIV co- infection. HPV type 11 may cause genital warts but is not a likely cause of cervical cancer. The presence of other sexually transmitted diseases, such as Chlamydia or hepatitis B, may help to identify women at high risk for cervical cancer, but they are not direct causes of cervical cancer. Following the abnormal pap smear findings, the next step in the diagnosis of this patient would be a colposcopy with biopsy of any visualized cervical abnormalities. At this point, HPV testing and typing would not add to or change the work-up, so they would not be necessary. HPV testing and typing can be helpful in the evaluation of women with lower grade cervical cytological abnormalities, such as ASCUS. The other tests noted may be performed later in the diagnostic work-up, after the results of the biopsies are known.

• Question 687:

  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 is associated with a reduced risk of osteoporotic fractures?

  A. family history of hip fractures
  B. estrogen deficiency
  C. body mass index of greater than 23
  D. tobacco use
  E. vision problems
  C. body mass index of greater than 23

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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 688:

  A 28-year-old man presents with vague complaints of fatigue, nausea, and dyspnea. He has had occasional episodes of hemoptysis and some burning with urination. Laboratory studies reveal a mild anemia and an elevation of both blood urea nitrogen (BUN) and creatinine. Urinalysis reveals the presence of blood, protein, and red cell casts. Antibodies against which of the following is the cause of this condition?

  A. platelet surface antigens
  B. basement membrane
  C. parietal cell antigens
  D. colonic mucosal cells
  E. macrophage receptors
  B. basement membrane

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  Explanation

  Goodpasture syndrome is characterized by antibasement antibodies, with the lungs and kidneys bearing the brunt of the damage. Antibodies against platelet surface antigens, parietal cells, antigens, receptors, and colonic mucosal cells are seen in autoimmune thrombocytopenia, pernicious anemia, myasthenia gravis, and ulcerative colitis, respectively.

• Question 689:

  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 negative predictive value (NPV) of this test for the diagnosis of CHF?

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

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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 690:

  A 23-year old male driver involved in a head-on motor vehicle collision is brought to the ER. On initial evaluation in the trauma unit, his blood pressure is 180/70 and his pulse is 56. After initial evaluation and resuscitation you obtain a CT scan of his head

  

  The finding on the imaging study is most commonly associated with injury to which of the following?

  A. the bridging veins
  B. the middle meningeal artery
  C. the sagital sinus
  D. the temporal artery
  E. the epidural artery
  B. the middle meningeal artery

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  Explanation

  The management of elevated intracranial pressure following traumatic injury has been extensively studied. Several interventions have been shown to be of benefit in the acute setting. The pressure can be relieved through mechanical means such as elevating the head of the bed to 30 degrees or by direct drainage of cerebrospinal fluid via a ventricular catheter. Administration of a hyperosmotic solution such as mannitol can decrease intracranial pressure by reducing brain water, increasing plasma volume and reducing blood viscosity. Additionally, if the ICP is refractory to these interventions, it is reasonable to consider a barbiturate coma or potentially a decompressive craniectomy. Hyperventilation is used only in the acute setting to keep PaCO2 around 35 mmHg, which functions to decrease intracranial pressure by decreasing intracranial blood volume through vasoconstriction. MRI would not be indicated initially, as it would not change your management. Severe head injuries are a frequent problem encountered in the field of trauma. CT scans are the primary diagnostic modality used to evaluate patients with suspected head injuries. Elevated intracranial pressure is a frequent result of severe brain injury either from brain swelling or mass effect from expanding hematomas. Subdural hemorrhages typically have a crescent shape and extend across suture lines covering the entire surface of one hemisphere. These are usually the result of the disruption of bridging veins. Epidural hematomas on the other hand have a biconvex lens appearance on CT scan. They typically develop afteran injury to the middle meningeal artery. Brain injury is generally greater in patients with subdural hematomas than in those with epidural hematomas.