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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 691:

  A 29-year-old woman complains of fatigue and decreased exercise tolerance. She takes no medications and denies changes in the color of the stool. Physical examination is significant for pale skin and conjunctivae. Stool was negative for blood. Laboratory evaluation revealed Hgb of 7.8 g/dL, reticulocytopenia, microcytosis, and hypochromia.

  The U.S. Preventive Services Task Force (USPSTF) recommends screening for iron deficiency in which of the following?

  A. asymptomatic persons over the age of 65 at risk for gastric cancer
  B. immigrants from developing countries
  C. asymptomatic infants at high risk
  D. pregnant women
  E. blood donors
  D. pregnant women

  ---

  Explanation

  Iron-deficiency anemia (IDA) is characterized by a low MCV, low ferritin, and a high erythrocyte protoporphyrin in serum. Microcytosis and hypochromia are the hallmark in the peripheral smear. Elevated erythrocyte protoporphyrin in serum can also be seen in anemia of chronic disease and chronic lead poisoning. The USPSTF recommends screening pregnant women for IDA, but found insufficient evidence to recommend for or against routine screening in other asymptomatic persons. However, the guidelines did recommend routine iron supplementation in asymptomatic infants 612 months of age who are at high risk of IDA. Infants are considered to be at high risk if they are living in poverty; are Black, Native American, or Alaskan Native; are immigrants from a developing country; are preterm or low birth weight; or if their primary dietary intake is unfortified cow's milk. The most common cause of cobalamin deficiency is pernicious anemia. Rarely, hypersecretion of gastric acid (i.e., Zollinger- Ellison syndrome) results in cobalamin deficiency.

  The peripheral smears in folate and cobalamin deficiency are indistinguishable, showing macrocytosis and hypersegmented neutrophils. Both methylmalonic acid and homocysteine levels become elevated with cobalamin deficiency. Folate deficiency is caused by decreased intake, increased utilization, or impaired absorption. Because body stores of folate are low, persons who have an inadequate consumption will become anemic in several months. The recommended amount of dietary folate is 400 g/day.

  Anemia is not a diagnosis in itself; it is an objective sign of the presence of a disease. It is always secondary to an underlying condition. In most cases, a thorough history and physical examination can help elicit the pathogenesis of the anemia and direct appropriate treatment.

• Question 692:

  A65-year-old White female presents to the office for her annual gynecologic examination. She has been a patient of yours for many years. She also sees you on a routine basis for treatment of hypertension and hypothyroidism. Her last pap smear was 5 years ago and she has never had an abnormal pap smear. She had a mammogram 1 year ago that was normal. She does not perform self- breast examination. She is without complaint today.

  Past medical 1. Hypertension for 15 years history: 2. Graves' disease, treated with radioactive iodine thyroid ablation at age 50 OB/GYN history: 1.

  Menarche at age 14 2. Four term pregnancies with vaginal deliveries (at age 22, 25, 27, and 32) 3. Total abdominal hysterectomy and bilateral salpingo oophorectomy (TAH/BSO) age 47 for fibroids 4. On estrogen replacement therapy from age 47 to 55 Past surgical 1. Appendectomy at age 16 history:

  2. TAH/BSO as noted above Medications: 1. Hydrochlorothiazide 25 mg daily 2. Levothyroxine 0.1 mg daily 3. Potassium chloride 20 meq daily Allergies: None Family history: Parents, siblings unknown as patient was adopted Children are alive and well without known chronic medical conditions Social history: Widowed for 5 years, has not been involved in a sexual relationship since the death of her husband; retired school teacher; college educated; does not smoke cigarettes, drink alcohol, or use drugs; walks 3045 min a day for exercise

  Which of the following vaccinations would be routinely recommended for this patient?

  A. hepatitis B vaccine
  B. measles, mumps, rubella (MMR) if patient does not recall having the measles
  C. pneumococcal conjugate vaccine (PCV-7)
  D. pneumococcal polysaccharide vaccine (PPV-23)
  E. hepatitis A vaccine
  D. pneumococcal polysaccharide vaccine (PPV-23)

  ---

  Explanation

  Explanations:

  Screening for osteoporosis in women 65 years old or older is a level B recommendation of the USPSTF, as detection and treatment of osteoporosis may reduce fracture risk. In women who have had a hysterectomy (with removal of the cervix) for reasons other than cervical cancer, pap smear screening of the vaginal cuff is not recommended and cytologic screening can be discontinued. Therapy with either estrogen alone (in women who do not have a uterus) or combined estrogen and progesterone (in women who have a uterus) in postmenopausal women is controversial. Based on findings of the Women's Health Initiative and other studies, the USPSTF gives a level D recommendation to the use of combined estrogen and progesterone therapy and level I recommendation for estrogen therapy alone for the prevention of chronic conditions. Screening for asymptomatic bacteruria in all populations other than pregnant women is given a level D recommendation. No benefit from the intervention has been found and overtreatment with antibiotics may produce harm. While mammography for breast cancer screening has been given a level B recommendation, both self-breast examination and clinical breast examination are level I recommendations, with insufficient evidence to show any benefit in morbidity or mortality.

  According to the Centers for Disease Control, diseases of the heart make up the most common cause of death in women in this age group. Heart disease is responsible for approximately one-third of all deaths in women aged 65 and older. Malignant neoplasms make up the next largest cause of death, followed by cerebrovascular diseases and chronic lower respiratory diseases. PPV-23 is recommended for all adults over the age of 65 and at younger ages for individuals at high risk for pneumonia or complications of pneumonia. These include persons with diabetes mellitus, chronic obstructive pulmonary disease, coronary artery disease, and those who have had a splenectomy or are functionally asplenic. The PCV-7 is recommended for the routine vaccination of children. Hepatitis B vaccine is recommended universally for children and for adults who are at high risk for the disease based on profession or lifestyle. Hepatitis A vaccine is recommended for children who live in certain areas of the United States in which the disease is prevalent and may be offered electively to persons traveling to endemic areas. The MMR vaccine is recommended to all children but is not indicated in adults. Rubella vaccination is recommended for women of childbearing age who may become pregnant and who do not have immunity to rubella, in an effort to reduce the risk of congenital rubella infection

• Question 693:

  A 13-year-old boy is brought into the emergency room with a laceration of his right arm. According to his parents, he received the injury when he fell on the ground while playing at the family farm about 1 hour ago. He has no known history of any medical problems. His parents say that they haven't brought him to the doctor in years. On questioning, they report that he only received one of his "baby shots" and they are not sure which one that was. On examination, he is healthy appearing. He is appropriately apprehensive but calm and consolable. His right arm has a 5 cm linear laceration with visible soil particles in and about the wound. The remainder of his examination is unremarkable. You carefully clean and irrigate the wound and then primarily repair the laceration with sutures.

  What immediate tetanus prophylaxis would be optimal in this case?

  A. IM injection of adult Td vaccine only
  B. IM injection of both adult Td vaccine and tetanus immune globulin (TIG)
  C. IM injection of Tdap only
  D. IM injection of TIG only
  E. IM injection of both Tdap and TIG
  E. IM injection of both Tdap and TIG

  ---

  Explanation

  Explanations:

  The disease tetanus is caused by an exotoxin produced by the anaerobic, gram-positive bacterium C. tetani. The spores of C. tetani are endemic in soil, particularly in agricultural areas. They can also be found in the intestines and feces of many animals. Human infection usually is the result of the introduction of the spores through a wound, such as a puncture or laceration. The spores can then germinate and toxins are released. Tetanus is characterized by unopposed muscle contractions and spasms.

  Autonomic nervous system manifestations, seizures, and difficulty swallowing may occur. Recovery may take months, but the disease is often fatal. In the developed world, most cases of tetanus occur in those who either were never vaccinated or who completed a primary vaccine series but have not had a booster in the preceding 10 years. The currently available vaccine is a toxoid which consists of a formaldehyde-treated toxin. It is available as a single antigen vaccine, combined with diphtheria (pediatric DT or adult Td) or combined with both diphtheria and acellular pertussis vaccine (DTaP). Whenever possible, tetanus toxoid should be given in combination with diphtheria toxoid to provide periodic boosting for both antigens. There is little reason to use single antigen tetanus toxoid alone. Management of a potentially contaminated wound initially involves local wound care. Necrotic tissue should be debrided, foreign material removed, and the wound irrigated. The need for active and/or passive immunization against tetanus depends on the wound and the patient's history of immunization. A person who has completed a primary series of three or more doses of tetanus toxoid vaccine will not require passive immunization with TIG, but may require a booster of dT or Tdap. For a clean, minor wound, a Td or Tdap booster would be indicated if it has been more than 10 years since the patient's most recent booster. For all other wounds, a booster would be indicated if it has been 5 years since the most recent booster.

  In a person who has not completed a primary series, who is completely unimmunized, or in whom the vaccine status is unknown, initiating passive immunization with Td or Tdap is indicated for all wounds. If the wound is clean and minor then TIG would not be recommended. For all other wounds, both Td and TIG would be indicated, as the initial doses of Td/Tdap may not produce immunity and TIG can provide immediate, temporary immunity. Antibiotic prophylaxis against tetanus is not useful. As noted in

  explanation 9 (above), Tdap is recommended as a substitute for a single Td dose in order to address the increasing rates of pertussis being encountered in the population. As the patient has no history of having completed a primary vaccine series and has a contaminated wound, the optimal management would be to provide both Tdap and TIG. If Tdap were not available, then utilizing Td and TIG would be an acceptable substitute, with a dose of Tdap to be given as part of his "catchup" series in the future.

• Question 694:

  You are asked to see a 64-year-old man with left lower quadrant abdominal pain that was admitted to the medicine service after a CT scan demonstrated diverticulitis of the sigmoid colon. There was no evidence for gross perforation and no abscess was identified. He had been admitted 6 months ago for the same problem and had an uneventful recovery.

  Which treatment do you recommend?

  A. antibiotics only
  B. antibiotics and sigmoidectomy prior to discharge
  C. emergent sigmoidectomy
  D. antibiotics and sigmoidectomy 12 weeks after discharge
  E. antibiotics, interval colonoscopy, and subsequent sigmoidectomy
  E. antibiotics, interval colonoscopy, and subsequent sigmoidectomy

  ---

  Explanation

  Diverticulitis is categorized based on its complications. Uncomplicated diverticulitis is defined as inflammation of colonic diverticuli that does not involve free intraperitoneal perforation, abscess formation, fistula formation, or colonic obstruction. This entity can be managed as an outpatient but may require inpatient admission if the pain is severe. The treatment of choice is broad-spectrum antibiotics. The majority of patients will respond well to this intervention. However, as the incidence of recurrence increases the rate of complications also rises. Therefore, it is recommended that surgical resection be performed after the second episode of diverticulitis. Prior to the operative intervention, it is important to rule out the presence of cancer. A colonoscopy should be performed after resolution of the inflammation and prior to surgical resection. It is much more sensitive than a barium enema. The operation is typically delayed until 46 weeks following discharge from the hospital. This provides adequate time for resolution of the inflammation and enables an adequate workup, which includes a colonoscopy.

• Question 695:

  A 50-year-old man presents to your office with fatigue and weakness. He first noticed it a few weeks ago while trying to hang pictures with his wife. His legs have begun to ache as he walks up stairs. He has lost about 20 lbs in the last 3 months. Most recently, he has found that he is more constipated and has trouble rising from the commode. Your physical examination reveals modest proximal weakness, no articular swelling, rash, or any other pertinent findings. Blood work from a recent insurance examination revealed:

  Sodium 142 meq/L; potassium 3.8 meq/L; chloride 107 meq/L; bicarbonate 29 meq/L; BUN 30 mg/dL; Cr 1.6 mg/dL; WBC 6.8; Hgb 13.6 g/dL;

  HCT 40%; MCV 88.0 m3; platelets 240,000/mm3;

  AST 200 U/L; ALT 250 U/L; alkaline phosphatase 70 U/L; bilirubin 0.3 mg/dL; ESR 40 mm/h. Along with a creatine phosphokinase (CPK), which of the following tests should be ordered first?

  A. muscle biopsy
  B. gamma glutamyl transferase (GGT)
  C. MRI of the lumbar spine
  D. ultrasound of the liver and gallbladder
  E. kidney ultrasound with renal artery Doppler
  B. gamma glutamyl transferase (GGT)

  ---

  Explanation

  The clinical features presented by the patient suggest a myopathy. It is often forgotten that serum transaminases are found in the muscle as well as the liver. Thus, a significant inflammatory myopathy may present with elevated serum transaminases in addition to symptoms. In this patient with normal alkaline phosphatase and bilirubin, initial measurement of the GGT would help rule out liver pathology and would be more appropriate initially than ultrasonography. Rhabdomyolysis may lead to renal dysfunction or even renal failure and a kidney ultrasound may eventually be appropriate, but a urinalysis would be recommended first. An MRI of the lumbar spine is not needed for this evaluation. It has long been established that there is an association between dermatomyositis, polymyositis, and malignancy. Although the malignancy risk is slightly higher in patients with dermatomyositis than with polymyositis, the malignancy association with both diseases is well established. The overall risk of cancer is highest in the first 3 years after the diagnosis of the myopathy, but it also continues over the individual's lifetime. Cancers most highly associated with inflammatory myopathy include lung, pancreatic, GI tract, non-Hodgkin lymphoma, and ovarian.

• Question 696:

  A 4-year-old boy returns for his second visit to the emergency room. Three days ago he was brought in with a 4-day history of fever up to 102. At that time, his physical examination was significant for injection of the oropharynx and an enlarged left anterior cervical lymph node. His left TM was nonbulging and nonerythematous. He was sent home on amoxicillin with a diagnosis of streptococcal pharyngitis. He returns today with a persistent fever, edema of both hands, bilateral conjunctivitis, and a polymorphous truncal rash.

  What is the most likely diagnosis?

  A. rickettsial infection
  B. drug hypersensitivity reaction
  C. measles
  D. Kawasaki disease
  E. Scarlet fever
  D. Kawasaki disease

  ---

  Explanation

  Kawasaki disease is the second most common systemic vasculitis in children. The diagnosis requires the presence of fever for at least 5 days and four of the five criteria: bilateral conjunctivitis (generally nonpurulent); oropharyngeal mucosal changes including pharyngeal injection, strawberry tongue, or injection or fissuring of the lips; nonfluctuant cervical lymphadenopathy, usually unilateral; polymorphous rash that is primarily truncal; and changes of the peripheral extremities, including edema or erythema of hands and feet, or desquamation of the finger/ toes, usually beginning periungally. The treatment of Kawasaki disease consists of high-dose aspirin and IVIG as a single dose infused over 12 hours. The role of corticosteroid as treatment is controversial. This therapy was abandoned after an initial report citing increased rates of coronary artery aneurysms. A few recent studies reveal successful treatment with methylprednisolone in children who failed therapy of IVIG, but it is not first line.

• Question 697:

  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.

  Before doing so, you explain to the patient that antibiotics such as gentamicin are often associated with which of the following?

  A. hepatotoxicity
  B. nephrotoxicity
  C. interstitial pulmonary fibrosis
  D. pulmonary edema
  E. splenomegaly
  B. nephrotoxicity

  ---

  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 698:

  A 24-year-old male is involved in a house fire. His sputum is carbonaceous and he has suffered second- and third-degree burns to 65% of his total body surface area (TBSA). He is intubated in the ED without difficulty. A capnometer is placed at the end of the endotracheal tube and there is positive change in color. Examination of his chest reveals bilateral equal breath sounds. Suddenly he experiences ECG changes and goes into cardiac arrest. Which of the following drugs is most likely to be responsible for this event?

  A. etomidate
  B. rocuronium
  C. succinylcholine
  D. midazolam
  E. ketamine
  C. succinylcholine

  ---

  Explanation

  Succinylcholine is a depolarizing neuromuscular blocking agent that can cause arrhythmias including bradycardia and junctional rhythms because of vasotonic effects. Additionally, succinylcholine is associated with a transient hyperkalemia that can be profound in patients with burns or those who have experienced significant crush injury and result in cardiac arrest.

• Question 699:

  A72-year-old African American male presents for a routine health examination. He states that he would like to have a "screening for cancer." In the United States, based on his sex, race, and age, what is the most likely malignancy for this patient?

  A. lung cancer
  B. prostate cancer
  C. colon cancer
  D. testicular cancer
  E. multiple myeloma
  B. prostate cancer

  ---

  Explanation

  Prostate cancer is the leading cancer in African American males in the United States. The cancer with the highest rate of mortality for the same subpopulation is lung cancer. Of African-American men diagnosed with a new cancer, approximately 42% will have prostate cancer, 14.6% lung cancer, and 10% colorectal cancer. The leading causes of cancer deaths in the same population are lung (28.4%), prostate (15.6%), and colorectal cancer (10.5%).

• Question 700:

  A 32-year-old woman complains of episodic confusion in the morning for the past 6 months. During one of these episodes, she was brought to the ER and her serum glucose was found to be 40 mg/dL. She was given intravenous dextrose and her symptoms resolved within 15 minutes. She has gained approximately 25 lbs during the past year. Which of the following would be the most appropriate next step?

  A. measure serum insulin and proinsulin 2 hours after a mixed meal
  B. MRI of the pancreas
  C. measure insulin, C-peptide, and sulfonylurea level on the initial blood sample in ER
  D. octreotide scan
  E. advise a high protein diet with frequent feedings
  C. measure insulin, C-peptide, and sulfonylurea level on the initial blood sample in ER

  ---

  Explanation

  The patient appears to have significant hypoglycemia and neuroglycopenia. The differential diagnosis includes medications such as sulfonylureas; alcohol; endocrine deficiency syndromes such as adrenal insufficiency, hypopituitarism, and hypothyroidism; surreptitious insulin administration; and insulinoma. The best way to establish the diagnosis is to measure the levels of each of these levels on the critical sample demonstrating hypoglycemia.