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

USMLE USMLE-STEP-2 Online Questions & Answers

• Question 171:

  A13-year-old boy is brought to the emergency department at midnight with a 4-hour history of right scrotal pain that was sudden in onset and associated with nausea and one episode of vomiting. On examination, he is in obvious distress. He has mild right lower abdominal tenderness, and high-riding, tender right testes.

  CBC and urinalysis are normal.

  Which of the following is the most appropriate next step in management?

  A. admit the patient to the hospital and place him on bed rest
  B. analgesics and a scrotal support
  C. antibiotic therapy
  D. schedule a testicular isotope scan
  E. urgent surgical exploration
  E. urgent surgical exploration

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  Explanation

  Testicular torsion presents with acute onset of scrotal pain, reflex vomiting, referred abdominal pain, and an elevated tender testis. If there is a high index of suspicion based on history and clinical examination, the patient should undergo an urgent surgical exploration. Delay in definitive therapy increases the risk of testicular loss secondary to ischemia. Isotope scan may demonstrate absence of testicular blood flow in torsion, and increased flow in orchitis or epididymitis. Although useful in the differential diagnosis, these nuclear medicine studies may not be readily available, and definitive therapy should not be delayed awaiting imaging. Orchitis and epididymitis present with a more insidious clinical course associated with the progression of the inflammatory process. There may be a concomitant urinary tract infection, and therapy includes analgesics and antibiotics.

• Question 172:

  An outbreak of influenza occurs across the United States in the early winter. Of individuals contracting influenza, a large proportion had received vaccinations earlier in the fall. Which of the following is the most likely explanation?

  A. The vaccine was manufactured improperly.
  B. The vaccine used did not contain antigen specific to the outbreak strain.
  C. A systemic storage problem with a major shipper damaged the vaccine.
  D. Due to unusually cold weather, people were more susceptible.
  E. The virus was especially virulent.
  B. The vaccine used did not contain antigen specific to the outbreak strain.

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  Explanation

  Manufacturing, storage, and shipping problems do occur. However, they have not been related to nationwide failures, although a major manufacturing problem in 2004 resulted in a major reduction in supply of vaccine. It is more likely that the vaccine in use is not completely protective against the prevalent viral strain. The WHO monitors influenza outbreaks worldwide. Based on strains present in outbreaks, and especially in the Pacific Rim, WHO makes a recommendation every spring regarding the antigens to use for the fall immunization campaign. Manufacturing then begins. Although their track record is good in this regard, antigen changes in influenza may reach the United States undetected or ahead of schedule

• Question 173:

  A31-year-old pregnant woman 67 weeks from her last menses comes to the emergency department of your hospital complaining of lower abdominal pain for 3 hours. The pain is diffused in the lower abdomen but worse on the right side. Her serum human chorionic gonadotropin (hCG) concentration is 9600 mIU/ mL.

  Which of the following is the strongest evidence that she has a tubal ectopic pregnancy?

  A. absence of an extrauterine sac on ultrasonography
  B. absence of blood on culdocentesis
  C. absence of a mass on bimanual examination
  D. absence of an intrauterine sac on ultrasonography
  E. her hCG concentration
  D. absence of an intrauterine sac on ultrasonography

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  Explanation

  At serum hCG concentrations above the discriminatory zone (usually about 4000 mIU/mL), transvaginal sonography should reveal an intrauterine pregnancy. The absence of such a finding suggests either an extrauterine pregnancy or a spontaneous abortion. Higher levels of hCG are necessary before an extrauterine gestational sac may be seen by sonography. At each week of gestation, hCG concentrations normally vary by a large amount. For this reason, a single measurement is not helpful, although serial measurements to determine whether the hCG fails to double in 48 hours is helpful to suggest a failing pregnancy (ectopic or intrauterine). Nonclotting blood obtained from the cul-de-sac by a culdocentesis may be the result of a ruptured ectopic pregnancy or a ruptured ovarian cyst. An adnexal mass is palpated in only 50% of women with an ectopic pregnancy.

• Question 174:

  A 59-year-old woman had a left modified radical mastectomy for intraductal carcinoma 2 years previously. She presents with confusion, lethargy, and thigh pain. X-rays reveal a lytic lesion in the shaft of the femur.

  Which of the following blood abnormalities is most likely?

  A. high glucose
  B. low calcium
  C. high potassium
  D. high calcium
  E. low magnesium
  D. high calcium

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  Explanation

  Hypercalcemia is a common complication of malignancy. Mechanisms include bone metastases, humoral secretion (e.g., osteoclast-activating factor), prostaglandin, or ectopic parathormone production and immobilization. Hypercalcemia is often manifested by confusion and lethargy. The other metabolic abnormalities usually are not associated with confusion. Therapy is directed at increasing renal calcium clearance and inhibiting further bone resorption. Saline infusion raises the glomerular filtration rate and decreases calcium reabsorption in the proximal tubule. Under life-threatening circumstances, the infusion may need to be aggressive, as much as 6 L of saline daily plus furosemide. Radiotherapy will do nothing for the calcium. Tamoxifen is an antiestrogen used in the treatment of breast carcinoma and other malignancies. When used in the presence of bone metastases, it may contribute to hypercalcemia. Chemotherapy will not decrease the calcium levels. Glucocorticoids have an antitumor effect and reduce tumor production of humoral mediators, but act slowly.

• Question 175:

  A 57-year-old man is on maintenance hemodialysis for chronic renal failure. Which of the following metabolic derangements can be anticipated?

  A. hypercalcemia
  B. hypophosphatemia
  C. osteomalacia
  D. vitamin D excess
  E. hypoparathyroidism
  C. osteomalacia

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  Explanation

  Chronic renal failure treated with hemodialysis results in predictable metabolic abnormalities. The kidneys fail to excrete phosphate, leading to hyperphosphatemia, and fail to synthesize 1,25(OH)2D3. Vitamin D deficiency causes impaired intestinal calcium absorption. Phosphate retention, defective intestinal absorption, and skeletal resistance to parathyroid hormone (PTH) all result in hypocalcemia. Hypocalcemia causes secondary hyperparathyroidism, and the excess PTH production worsens the hyperphosphatemia by increasing phosphorus release from bone. These derangements impair collagen synthesis and maturation, resulting in skeletal abnormalities collectively referred to as renal osteodystrophy. Osteomalacia, osteosclerosis, and osteitis fibrosa cystica may all be seen.

• Question 176:

  A92-year-old man is referred from his nursing home for evaluation of lethargy. Examination is unrevealing, but laboratory results are significant for a serum sodium level of 118 meq/L (normal, 135 148). Serum osmolality is 260, urine osmolality is 450, and urine sodium is 80. Which of the following is the most likely cause of this patient's lethargy?

  A. hyperglycemia
  B. hyperlipidemia
  C. hyperproteinemia
  D. SIADH
  E. diabetes insipidus
  D. SIADH

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  Explanation

  Hyponatremia is a common metabolic derangement. Facititious hyponatremia is seen with severe hyperlipidemia or hyperproteinemia (which lower plasma water content) and with hyperglycemia due to water movement out of cells. Most patients with hyponatremia are hypoosmolar and the diagnosis is based on an estimation of extracellular fluid (ECF) volume status. Decreased ECF volume and hyponatremia are associated with diuretic use, diarrhea, and dehydration. Expanded ECF volume due to decreased effective circulating volume and increased ADH secretion may result in edema and hyponatremia as often seen with congestive heart failure, cirrhosis of the iver, and nephritic syndrome. Euvolemia and hyponatremia can be due to hypothyroidism, drenal insufficiency, and other conditions associated with the SIADH. Diabetes insipidus is a cause of hypernatremia.

• Question 177:

  A 46-year-old woman presents with a 4-hour history of left flank pain with fever and chills. On examination, her temperature is 103°F, pulse rate is 120/min, re spiratory rate is 40/min, and supine BP is 80/40 mmHg. She has marked tenderness over the left flank and left upper quadrant of the abdomen without rebound. Urinalysis shows multiple red blood cells (RBCs), multiple WBCs, and WBC casts.

  Which of the following is the most likely diagnosis?

  A. appendicitis
  B. pyelonephritis
  C. cholelithiasis
  D. diverticulitis
  E. pelvic inflammatory disease
  B. pyelonephritis

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  Explanation

  Detection of leukocyte casts is pathognomonic for pyelonephritis. Common symptoms include fever, shaking chills, nausea, vomiting, and diarrhea. Flank tenderness over the affected kidney is very common

• Question 178:

  A 55-year-old woman has a bloody discharge from her left breast. A mammogram discloses a cluster of microcalcifications 3 cm beneath her left nipple.

  Which of the following is the best next step in her evaluation?

  A. cytologic evaluation of the nipple discharge
  B. fine-needle aspiration under radiologic guidance
  C. MRI of the breast and axillary nodes
  D. image-guided percutaneous biopsy of the left breast
  E. segmental mastectomy
  D. image-guided percutaneous biopsy of the left breast

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  Explanation

  Both the bloody nipple discharge and the microcalcifications are indications for a breast biopsy. Although there are benign-appearing radiographic calcifications, clusters of calcification are associated with a 25% chance of a cancer. An image-guided percutaneous biopsy is preferred because a fine- needle biopsy has about a 20% false negative rate. Cytology is a screening tool. In the presence of significant risk factors for cancer, a tissue diagnosis is mandatory. Imaging studies are also screening tools with a false negative and a false positive rate, making such studies inappropriate fordiagnosis

• Question 179:

  Why does ligation of the hypogastric (internal iliac) artery effectively control intractable pelvic hemorrhage?

  A. There is no collateral circulation to the uterus.
  B. Uterine blood flow is stopped.
  C. Arterial pulse pressure to the uterus is reduced.
  D. Clotting in uterine capillaries is enhanced.
  E. Blood flow is shunted to the ovarian veins.
  C. Arterial pulse pressure to the uterus is reduced.

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  Explanation

  Bilateral hypogastric artery ligation converts the arterial system into a venous system; thereby, reducing the pulse pressure by as much as 85%. Subsequent menstrual function and fertility are normal, in part because of the rich collateral circulation to the uterus. The procedure is successful in approximately 50% of cases. The procedure is not technically easy to perform, and an intimate knowledge of the local anatomy is essential to prevent injury to the hypogastric vein or ureter. Uterine hemorrhage not controlled by other means requires a hysterectomy

• Question 180:

  A 50-year-old man presents to the emergency department for increasing abdominal distention and jaundice over the last 46 weeks. Examination reveals mild jaundice, spider angiomas, and ascites.

  Enlarged veins are noted around the umbilicus.

  For above patient with jaundice, select the one most likely diagnosis.

  A. hepatitis A
  B. hemolysis
  C. choledocholithiasis
  D. biliary stricture
  E. choledochal cyst
  F. pancreatic carcinoma
  G. liver metastases
  H. cirrhosis
  I. pancreatitis
  H. cirrhosis

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  Explanation

  Chronic liver disease, such as cirrhosis, may be a cause of jaundice. Clinical features such as spider angiomas, ascites, and varices suggest cirrhosis.