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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 461:

  A 35-year-old woman with a history of major depressive disorder is brought into the ED by her boyfriend. He believes she may have overdosed on pain medication in an effort to hurt herself. He gives you three medication bottles which he discovered empty and states that they were nearly full before leaving for work earlier that morning. However, the timing of the ingestion is unclear. All three of the bottles apparently held acetaminophen- containing medications. Examination of the patient reveals a tired- appearing woman complaining of nausea and right upper quadrant abdominal pain. Which of the following is the worst prognostic indicator if present in this patient?

  A. arterial pH greater than 7.3
  B. arterial lactate greater than 3.5 mmol/L
  C. initiation of therapy 8 hours after acetaminophen ingestion
  D. "probable-risk" of hepatotoxicity by the Rumack-Matthew nomogram
  E. a history of chronic acetaminophen abuse
  B. arterial lactate greater than 3.5 mmol/L

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  Explanation

  When acetaminophen is taken in normal doses, it is conjugated in the liver to harmless glucuronide and sulfate metabolites. These metabolic pathways become easily overwhelmed in the setting of a large overdose, however. If this occurs, the cytochrome P450 system directs conversion of the excess acetaminophen to a compound called NAPQI, which is conjugated with glutathione to form a nontoxic mercapturate metabolite. Once glutathione stores are exhausted in the liver, however, the excess NAPQI combines with proteins within hepatic cells causing hepatic cell death. Taurine is a mercaptan- containing amino acid involved in bile acid biochemistry. Citrulline aids in the detoxification and elimination of ammonia. Ornithine plays an important role in the urea cycle.

  N-acetylcysteine should be administered as promptly as possible for treatment of acetaminophen overdose. It works by helping restore hepatic glutathione stores and by providing sulfhydryl groups that bind toxic metabolites. N-acetylcysteine is administered orally in the form of an initial loading dose (140 mg/kg) followed by 17 doses (70 mg/kg each) given every 4 hours. In addition to this oral therapy, the Food and Drug Administration (FDA) approved 21-hour and 48-hour long intravenous treatment regimens in 2004. Left untreated, acetaminophen overdose carries a significant risk for hepatic failure and subsequent death depending on the amount of acetaminophen ingested, the presence of any preexisting liver disease, and interactions with any other medications that induce cytochrome P450 enzyme activity. Naloxone, flumazenil, and physostigmine are given as antidotes for toxicity related to opioid analgesics, benzodiazepines, and muscarinic receptor blockers, respectively.

  Poor prognosis is associated with elevated serum lactate levels (above 3.5 mmol/L), acidemia (arterial pH less than 7.3), renal failure, and coagulopathy. The Rumack-Matthew nomogram provides a means of determining whether an individual falls into the possible-, probable-, or high-risk categories for developing hepatotoxicity based on serum acetaminophen levels and the number of hours since ingestion. Therapy with N-acetylcysteine is most effective if begun within 8 hours of the toxic ingestion but still has proven benefit if started within 24 hours

• Question 462:

  Parents bring you a 9-month-old boy they recently have adopted from western Russia. They have sparse medical records of the child's past. They do know that the boy was the result of a sexual assault on the mother and was given up at birth. The child has been in a "baby home" for 5 months. The records which accompanied the boy indicate that there had been some testing done. These tests include HIV, hepatitis B and C serologies, and a rapid plasma reagin (RPR), all of which are negative at 8 months of age. There is what appears to be a Russian immunization record as well. It seems to indicate that the child has had three diphtheria, tetanus, pertussis (DTP), three oral polio, and three hepatitis B vaccinations. There is also an indication that BCG (Bacille Calmette-Guin) was given.

  The parents are concerned about fetal alcohol syndrome (FAS). Which physical feature is most consistent with FAS?

  A. smooth philtrum
  B. single palmar crease
  C. hypertelorism
  D. synophrys (confluent eye brows)
  E. low set ears
  A. smooth philtrum

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  Explanation

  Repeating all serologies is important. The prior negative testing should be included in the medical record, but should not dissuade one from confirming the result. The collection of stool for ova and parasites (O + P) is an important evaluation but should not be the only testing performed. ACBC is not an adequate screen for infections.

  The diagnosis of FAS includes findings of characteristic facies, growth retardation, and CNS impairment. The characteristic facies of FAS includes flat philtrum, thin upper vermilion border, short palpebral fissures, micrognathia, microphthalmos, and microcephaly.

  BCG is a common vaccine administered in countries outside of the United States. The presence of a positive reaction to a PPD in a child who has had a prior BCG is still concerning. The presence of a 15- mm reaction is considered positive and warrants a CXR and initiation of anti TB treatment. The negative CXR would indicate TB exposure, and INH alone is recommended. Sputum collection is usually unwarranted in asymptomatic children.

• Question 463:

  A 17-year-old male is evaluated for a painless neck mass. You assess the mass as lymphadenopathy and arrange for a biopsy. The pathology report subsequently notes the presence of Reed-Sternberg cells.

  Which of the following is the most likely diagnosis?

  A. Hodgkin lymphoma
  B. non-Hodgkin lymphoma
  C. metastatic testicular cancer
  D. acute lymphocytic leukemia
  E. papillary carcinoma of the thyroid
  A. Hodgkin lymphoma

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  Explanation

  The Reed-Sternberg cell can be classified as the classic type, the mononuclear variant, the lymphocytic histiocytic variant, lacunar and pleomorphic variant. The classic Reed-Sternberg cell is a binucleated cell that contains an ovoid-shaped nucleus with regular contours and prominent eosinophilic nucleoli. Cytoplasm is abundant and eosinophilic. On cytogenetic studies, the Reed-Sternberg cells are either aneuploid or frequently hypertetraploid. The classic Reed-Sternberg cell is thought to be an end-stage cell that does not divide. The mononuclear variants of the Reed-Sternberg cells (so-called Hodgkin cells) could be identified in any type of Hodgkin disease, but they are not diagnostic of Hodgkin's.

• Question 464:

  Bupivacaine is a local anesthetic agent that is much more potent and the duration of action of which is considerably longer than procaine. Possible reasons for this difference include which of the following?

  A. higher partition coefficient for bupivacaine than for procaine
  B. covalent binding to the receptor site
  C. lower protein binding of bupivacaine than procaine
  D. decreased rate of metabolism of procaine compared to bupivacaine
  E. bupivacaine constricts blood vessels
  A. higher partition coefficient for bupivacaine than for procaine

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  Explanation

  Local anesthetics exist in solution in both uncharged base and charged cationic forms. The base diffuses across the nerve sheath and membrane and then re-equilibrates within the axoplasm. It is intracellular penetration of the cation into, and attachment to a receptor at a site within the sodium channel, that leads to inhibition of sodium conductance and ultimate conduction blockade. Bupivacaine is typical of amide- linked local anesthetics with high anesthetic potency and long duration of action (class III).

  Procaine is typical of class I agents that are ester linked and have low anesthetic potency and short duration of action. Important features of group III compounds include: (1) high degree of lipid solubility or high partition coefficient that aid in penetration of the drug, (2) high degree of protein binding that aids in attachment of the drug once it has penetrated the cell, and (3) pKa closer to pH = 7.4 so that more of the drug is in the unionized form and is free to penetrate the membrane. Esterlinked anesthetics, such as procaine, are rapidly metabolized by pseudocholinesterases, whereas bupivacaine is slowly degraded by hepatic enzymes

• Question 465:

  A 64-year-old diabetic male undergoes a right hemicolectomy for an adenocarcinoma of the cecum. On the first postoperative night, he becomes tachycardic and is noted to have a temperature of 102.8. His surgical incision is tender with erythema and murky discharge.

  Which of the following is the most important intervention?

  A. begin broad-spectrum antibiotics, Tylenol, and a cooling blanket
  B. open the wound and begin hyperbaric oxygen treatment
  C. apply sterile warm compress over the incision and replace dressing
  D. open the wound, send for Gram's stain of the fluid and emergent radical debridement
  E. postoperative fever evaluation including sputum, urine, and blood cultures
  D. open the wound, send for Gram's stain of the fluid and emergent radical debridement

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  Explanation

  Postoperative wound infections usually occur between the fifth and eighth postoperative days. Evidence of a wound infection within the first 24 hours after surgery should alert the physician to the possibility of necrotizing fasciitis. Necrotizing fasciitis is a lifethreatening infection most commonly caused by clostridial myositis and hemolytic streptococcus. In addition to spiking temperature, the patient may be septic with tachycardia, leukocytosis, and hemodynamic instability. On examination of the wound, crepitus (gas in the soft tissue) and a dishwater-appearing effluent may be apparent. Early diagnosis by opening the wound and sending a Gram's stain is critical. The Gram's stain will reveal a mixed flora of ramnegative rods and gram-positive cocci. Although broad-spectrum antibiotics are indicated, definitive treatment requires emergent aggressive debridement of the affected tissues. Hyperbaric oxygen treatment has no role in the acute management of necrotizing fasciitis. Diabetic patients are especially prone to necrotizing fasciitis. Fournier's gangrene is a type of necrotizing fasciitis that affects the groin and perineum. The mortality rate can be as high as 75%.

• Question 466:

  An 80-year-old woman is admitted to the medical service for treatment of a UTI. While she is hospitalized, she is evaluated for confusion. On her mental status examination (MSE), she appears somnolent at times, fluctuating with an alert state. She is not cooperative, is hostile, and clearly is hallucinating at times. Her insight and memory are poor. The differential diagnosis includes both delirium and dementia.

  Which of the following is the most appropriate pharmacotherapy for her behavioral management?

  A. low-dose diphenhydramine (Benadryl)
  B. low-dose donepezil (Aricept)
  C. low-dose haloperidol (Haldol)
  D. low-dose lorazepam (Ativan)
  E. low-dose risperidone (Risperdal)
  E. low-dose risperidone (Risperdal)

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  Explanation

  This case demonstrates a classic presentationfor delirium. Delirium can present with many symptoms, including aggressiveness, hostility, memory impairment, psychotic symptoms (especially visual hallucinations), and overall uncooperativeness, such as pulling out IVs and getting out of bed. While these symptoms are common in delirious patients, they are not specific for delirium and can be seen in many psychiatric illnesses, including dementias, psychotic disorders, substance use disorders, personality disorders, and others.

  The hallmark of delirium is a fluctuating level of consciousness over time, ranging from sedation to agitation. Diphenhydramine can be sedating but, due to its anticholinergic side effects, can also worsen delirium and cause urinary retention and constipation, especially in the elderly. Anticholinesterase inhibitors such as donepezil may be indicated for mild-tomoderate dementias, especially Alzheimer dementia. It is not indicated for the treatment of delirium and it would be difficult to diagnose a dementing illness in the context of a delirious state. Giving benzodiazepines such as lorazepam may be useful for agitation caused by a delirium, but they can also disinhibit a patient and cause further agitation, especially in older individuals. A benzodiazepine would be the preferred treatment of alcohol withdrawal delirium (delirium tremens [DTs]), however. A low dose of antipsychotic would be the best choice to decrease the agitation in a delirious patient. While a high-potency medication such as haloperidol can be used, it is more likely to cause extrapyramidal side effects than a second-generation (or atypical) antipsychotic such as risperidone.

• Question 467:

  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.

  After the treatment given above, what would be the recommended "catch-up" immunization schedule to protect against tetanus?

  A. Td every 5 years
  B. Td in 6 months then booster every 10 years
  C. Td in 4 weeks and 612 months then booster every 10 years
  D. Td in 2 months, 4 months, 1518 months, and 5 years and then booster every 10 years
  E. TIG IM every 510 years
  C. Td in 4 weeks and 612 months then booster every 10 years

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  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 468:

  During initial exploration in a patient scheduled to undergo a right hemicolectomy for colon cancer, a deep 4-cm liver mass is seen in the right lobe of the liver. The left lobe appears to be normal. Intraoperative biopsy of the lesion is positive for metastatic colon cancer. The best management of this patient includes which of the following?

  A. Immediately close the patient and refer for chemotherapy only.
  B. Perform right hemicolectomy only.
  C. Perform right hemicolectomy and right hepatic lobectomy.
  D. Perform right hemicolectomy and wide excision of the liver lesion.
  E. Perform liver resection only.
  B. Perform right hemicolectomy only.

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  Explanation

  Colon cancer is the most common metastatic lesion of the GI tract to the liver. Approximately 50% of patients with colorectal cancer will have liver involvement. Generally, synchronous liver metastasis should not be resected during the initial operation for the primary tumor. Only a solitary, small, peripherally located lesion in a hemodynamically stable patient would be an acceptable indication for a wedge resection. Otherwise, the planned colon resection should be completed. A second procedure can be planned after a thorough metastatic evaluation is completed using various diagnostic modalities such as intraoperative ultrasound, CT, MRI, and/or PET scan. A delay of weeks to months between surgeries has not been shown to have a negative impact on long-term survival. The delay may help select patients who may benefit the most and exclude those who develop widespread metastatic disease during the interval. Chemotherapy only is inappropriate because, even in the presence of metastatic disease, the primary colon carcinoma should be resected to prevent later complications such as bleeding, perforation, or obstruction. The 5-year survival rate following resection of isolated hepatic metastasis from colorectal cancer now exceeds 50%.

• Question 469:

  A35-year-old woman with two prior term pregnancies presents for her first prenatal visit at 12 weeks' gestation. She recalls having had hypertension near the end of her first pregnancy. She believes her blood pressure has been normal since, but admits that she rarely seeks preventive health care visits, and that her last examination by a physician was more than 2 years ago. Today, you find her blood pressure to be 160/100.

  Which of the following antihypertensive agents would be contraindicated for management of her hypertension during pregnancy?

  A. labetalol
  B. alpha-methyldopa
  C. enalapril
  D. nifedipine
  E. hydralazine
  C. enalapril

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  Explanation

  The angiotensin-converting enzyme inhibitors (and angiotensin receptor blockers) are contraindicated in pregnancy due to their potential to cause decreased fetal renal perfusion, ultimately resulting in fetal oliguria, oligohydramnios, renal tubular dysplasia, and neonatal anuric renal failure, as well as defects in ossification of the fetal skull. These adverse effects occur during the second and third trimesters of pregnancy. If a woman conceives while taking an angiotensin-converting enzyme inhibitor, she should be changed to another agent during the first trimester.

  Preeclampsia causes 5070% of cases of hypertension in pregnancy. Mild preeclampsia is characterized by an increase in systolic BP of 30 mmHg, an increase in diastolic BP of 15 mmHg, or an absolute reading of 140/90 mmHg in a pregnant patient with minimal proteinuria and pathologic edema. A systolic BP greater than 160/110 mmHg with significant proteinuria (>5000 mg/24 h) and evidence of end-organ damage indicate severe preeclampsia. End organ damage results from increased vascular reactivity, third spacing of fluids, and platelet activation. Complications include oliguria, the syndrome of hemolysis, elevated liver function tests, and low platelets (HELLP) and eclamptic seizures. Seizure prophylaxis is effective in both primary prevention of eclampsia and in prevention of recurrent seizures. Fetal macrosomia occurs more commonly in pregnancies complicated by diabetes. Abnormal labor progress and postpartum hemorrhage as well as breech presentation are not more common in pregnancies complicated by preeclampsia.

• Question 470:

  A 50-year-old man comes to the emergency room (ER) with a history of vomiting of 3 days' duration. His past history reveals that for approximately 20 years he has been experiencing epigastric pain that lasts for 23 weeks during spring and autumn. He remembers getting relief from pain by taking milk and antacids. Physical examination showed fullness in the epigastric area with visible peristalsis, absence of tenderness, and normal active bowel sounds.

  What is the most likely diagnosis?

  A. gastric outlet obstruction
  B. small bowel obstruction
  C. volvulus of the colon
  D. incarcerated umbilical hernia
  E. cholecystitis
  A. gastric outlet obstruction

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  Explanation

  In a patient who is known to have had symptoms of peptic ulcer disease for many years and presents with nausea and vomiting, one should consider gastric outlet obstruction. The bstruction can be the result of an exacerbation of the ulcer and subsequent edema or it can be secondary to scar tissue formation. These patients typically describe the sensation of epigastric fullness and demonstrate visible peristalsis going from left to right. A succussion splash may be audible. The history of periodicity and pain relief by taking antacids also favors a diagnosis of previous peptic ulcer disease. Patients with an umbilical hernia will have a mass in the region of the umbilicus. Patients with acute cholecystitis usually present with the sudden onset of pain, radiating to the back, with fever and chills. Volvulus of the sigmoid colon presents with constipation and abdominal distention but vomiting is a late feature. Small bowel obstruction would be associated with a history of colicky abdominal pain, nausea, and vomiting.

  Additionally, patients with small bowel obstruction usually have hyperactive highpitched bowel sounds on examination.