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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 121:

  The results of your study find two risk factors associated with the development of the disease that you are studying. Risk factor "X" was found to have an odds ratio for the development of the disease of 2.5 (95% CI:

  1.34.0). Risk factor "Y" had an odds ratio of 1.9 (95% CI: 1.13.3).

  Which of the following statements is true?

  A. Both risk factors X and Y are now proven to cause the disease.
  B. Persons with risk factor X will have a worse prognosis than those with risk factor Y.
  C. Risk factor X was more common in your study population than risk factor Y.
  D. Both risk factors occurred more commonly in persons with the disease than in persons who did not have the disease.
  E. For every 100 people with the disease, 25 will have risk factor X and 19 will have risk factor Y.
  D. Both risk factors occurred more commonly in persons with the disease than in persons who did not have the disease.

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  Explanation

  Explaination:

  All types of study designs have potential benefits and drawbacks and it is important to understand this when designing research or reviewing research reports. A cross-sectional study is one in which information is gathered from a certain population at one point in time with no follow-up period. This type of study is very useful for the determination of the prevalence of a disease or risk factor in a population at a certain point in time. Cross-sectional studies cannot determine cause and effect because there are no interventions being made and there is no follow-up. A case-control study is very useful and efficient at studying diseases that occur rarely. In a case-control study, persons with a disease are identified and then information is determined by looking back in time (i.e., retrospective review). Apopulation of those without the disease (controls) is also defined and studied in the same way.

  The prevalence of a risk factor in the cases and controls can then be determined and compared. A case- control study cannot prove cause and effect, but it can be a powerful tool to determine risk factors that can generate hypotheses for further study. Acohort study is one in which a population is defined and then followed over time. A cohort study may be either prospective or etrospective. Cohort studies can be used to describe the incidence of diseases over time or to determine associations between predictors and outcomes. Cohort studies are inefficient for the study of rare outcomes, as a very large sample size would be required in order to find a few events. Aprospective, randomizedcontrolled trial is the gold standard study for determining the effect of a treatment or intervention. It is not the type of study that would be used to determine the prevalence of a disease in a population or to determine what risk factors are associated with the development of a disease. A meta-analysis is a systematic review of completed research studies. By evaluating similarly done studies, the meta-analysis technique can allow for an evaluation of a body of literature and can be used to increase the overall statistical power by creating a larger sample by combining studies.

  The odds ratios given show that both risk factors X and Y occurred more often in those with the disease (cases) than they did in those without the disease (controls). Neither of the CIs given cross 1, therefore, these are statistically significant findings. We cannot use this type of study to definitively prove cause and effect, therefore option A is false. While risk factor X had a higher odds ratio for the development of the disease than risk factor Y, no prognostic data are supplied and none can be inferred from the information given, therefore B is false. The odds ratios as given in this case compare the prevalence of a risk factor in the case group with the control group, not the prevalence of one risk factor compared to another. For this reason, we cannot say which risk factor is more common in the population and option C is false. No absolute numbers are presented in this question and therefore we cannot determine how often each of the risk factors occurs in our population, so E is false as well

• Question 122:

  The most common cause of surgery in a patient with Crohn's disease is which of the following?

  A. carcinoma
  B. fistula
  C. bleeding
  D. obstruction
  E. abscess
  D. obstruction

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  Explanation

  Crohn's disease is a chronic inflammatory disease of the GI tract of unknown etiology. Both medical and surgical treatments are palliative in nature--there is no known "cure." pproximately 70% of patients with Crohn's disease will require an operation during their lifetime. The most common indication for surgery is recurrent bowel obstruction, followed by perforation with abscess and fistula formation.

• Question 123:

  An 82-year-old woman is admitted to the surgical ward after suffering a fracture of her right hip due to a fall down her stairs. Her surgery and recovery are uneventful, but 3 days later, the nurses are frustrated when she does not let them take her vitals or draw blood. On interview, she exhibits drowsiness with occasional agitation. She is unable to answer questions well and is oriented only to person. She also picks at the empty air and begins yelling and swinging at the nurse who is present. 90.

  Which of the following most likely represents her mortality rate in 6 months after discharge?

  A. 020%
  B. 2040%
  C. 4060%
  D. 6080%
  E. 80100%
  B. 2040%

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  Explanation

  Explanations:

  This patient exhibits signs and symptoms of delirium. An EEG is very sensitive for delirium. Localized spikes would be seen in a patient with seizure activity. Random activity is characteristic of the normal, awake state. Lowvoltage fast activity is very specific to delirium secondary to alcohol or sedative/hypnotic withdrawal. Triphasic delta waves are characteristic of delirious states caused by hepatic failure. All other causes of delirium, however, demonstrate diffuse slowing on EEG. Medications, such as antipsychotics and benzodiazepines, may be helpful in reducing the agitation often seen in delirium. Soft restraints may also be necessary to permit the treatment team to perform appropriate examinations, tests, or procedures and to prevent the pulling out of intravenous access, feeding tubes, and so on. Behavioral interventions may be employed to reinforce orientation to person, place, and time. Some of these interventions may include the use of pictures, lights, clocks, or calendars. The primary and essential approach in the management of patients with delirium, however, is to determine and treat the underlying cause. The presence of a delirium is a poor prognostic sign. The mortality rate for 1 year after a delirium is approximately 50%. The mortality rate for 6 months after an episode of delirium is approximately 25%.

• Question 124:

  An 8-year-old boy is brought in for evaluation by his parents, who are worried about his behavior in school. Recently, he has become increasingly upset about attending school. Whereas he had always enjoyed being read to as a small child, he has appeared easily frustrated when reading or being asked to write. During those times, he will often disrupt the class, and this has led to his parents being asked to remove him from the school.

  Which of the following additional diagnoses most likely would be present in this patient?

  A. ADHD
  B. autistic disorder
  C. major depressive disorder
  D. mental retardation
  E. tic disorder
  A. ADHD

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  Explanation

  Explanations:

  This child may have reading disorder, a type of learning disorder characterized by reading achievement below expected given measured intelligence and age (DSM IV-TR). The Bender Visual Motor Gestalt Test is not a diagnostic test, but it may be used to identify perceptual performance difficulties. Projective psychological tests, such as the Children's Apperception Test and the Rorschach, are not useful for intelligence testing. The Reitan-Indiana Neuro-psychological Test is helpful for children with suspected brain damage. In diagnosing learning disorders, it is essential to measure intelligence in order to compare the results with any discrepancies in achievement. The Wechsler Intelligence Scale for Children is one of the most widely used for this purpose. Many patients with learning disorders, such as reading disorder, have comorbid axis I disorders. It is not uncommon to find other learning disorders, such as mathematics disorder, present as well. Conditions such as autistic disorder and mental retardation make it difficult to diagnose a learning disorder. If another deficit in functioning is present, the learning difficulties must be in excess of those assoiated with it (DSM IV-TR). Depressive symptoms are not unusual in individuals with learning disorders, given the problems with school performance and peer relationships. Tic disorders are not significantly increased in those with reading disorder.

  There is a high level of correlation between ADHD and reading disorder, with figures up to 25%; there may also be a relationship between the etiologies associated with each.

• Question 125:

  A19-year-old male who moved to your city 3 months ago comes to your office complaining of dry cough for the past 23 months. Along with the cough, he has had some shortness of breath with exertion. He denies fever, chills, nausea, vomiting, wheezing, and sneezing. The cough occurs mostly in the morning and improves as the day goes on. He denies similar complaints in the past and has no history of allergies. He says that his father had eczema and an allergy to eggs.

  Which of the following properties of albuterol makes it a more appropriate choice than epinephrine for relief of acute episodes of bronchoconstriction?

  A. rapid onset of action
  B. longer duration of action
  C. specificity for beta-1 receptors
  D. specificity for beta-2 receptors
  E. direct activation of both alpha- and beta-receptors
  D. specificity for beta-2 receptors

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  Explanation

  This patient is manifesting symptoms consistent with asthma. With the history of recently moving to a new area, along with a family history of allergies and eczema, his asthma may be further classified as allergic asthma. Episodic symptoms of cough, dyspnea, and wheezing are likely to occur. The diagnosis of asthma is made by demonstrating reversible airway obstruction. Airway obstruction is likely to be manifested by a reduction in the FEV1. An increase in the FEV1 of 15% after the use of a bronchodilator is the definition of reversibility. A CXR is most likely to be normal. Numerous cardiac conditions, such as CHF, cardiomyopathies, or pericardial effusions, may result in cardiomegaly on a CXR. Diffuse infiltrates may be seen with infections, interstitial lung disease, or other conditions. Flattened diaphragms would be consistent with prolonged obstructive lung disease, such as emphysema.

  The treatment of choice for the prevention of symptoms in all stages of asthma other than mild intermittent is inhaled steroid. All patients with asthma should also have a short-acting bronchodilator for acute symptomatic relief. A leukotriene modifier would be an alternative recommendation and might be a good addition to an inhaled steroid, as they also have FDA indications for patients with allergic rhinitis.

• Question 126:

  A38-year-old woman presents to the ER with heavy vaginal bleeding. A pelvic examination using a speculum to visualize the cervix reveals a large, friable, fungating cervical mass. On bimanual examination, the mass extends to the right pelvic sidewall. A biopsy from a recent gynecologic visit reveals invasive squamous cell carcinoma of the cervix. An abdominal/pelvic CT scan shows enlarged pelvic lymph nodes and right hydronephrosis. Her hematocrit (HCT) in the ER is 24%, but she is hemodynamically stable with a BP of 124/70 and a pulse of 73. The cervical mass is actively bleeding.

  Your initial treatment of the vaginal bleeding in the ER only partially controls the bleeding, and she is requiring frequent retreatment. The best definitive treatment to control the bleeding at this time is which of the following?

  A. emergency bilateral hypogastric artery ligation
  B. uterine artery embolization
  C. emergency high-dose radiation therapy
  D. emergency radical hysterectomy
  E. loop excision electrocautery procedure (LEEP)
  C. emergency high-dose radiation therapy

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  Explanation

  A woman with advanced cervical cancer may present emergently with heavy vaginal bleeding. Often, the bleeding can be controlled for 24 hours by packing the vagina with a packing soaked in Monsel solution. The patient is kept on bedrest, and the packing is changed every 24 hours. If packing the vagina does not control the bleeding, then emergent radiation therapy is warranted if the patient has not had previous radiation treatment. Hemorrhage is usually controlled within 2448 hours of initiating external beam therapy. If radiation therapy fails, then the next best treatment is arterial embolization of either the uterine or hypogastric arteries. However, embolization may result in tumor hypoxia and decrease the sensitivity of the tumor to radiation.

  Arteriography with embolization may allow visualization of the bleeding vessel with direct embolization of the source. Arterial embolization has several risks including infarction of distal tissue, infection, and femoral artery thrombosis. If embolization is not available or not successful, bilateral hypogastric artery ligation is an option. In this patient, surgical therapy with radical hysterectomy is not an appropriate treatment because this patient's disease has spread beyond the cervix. This procedure would result in transection of the tumor and lead to further bleeding complications. This patient has at least a stage IIIB tumor, and the best treatment for her is chemoradiation

• Question 127:

  One of your responsibilities at the community health center is to serve as director of the tuberculosis (TB) screening and prevention program.

  Which of the following statements regarding the management of an asymptomatic person with a positive TB skin test is true?

  A. Because of the development of resistant TB strains, recent converters both with and without symptoms should be treated with four drug therapy.
  B. A pregnant woman with a positive skin test should not have a chest x-ray until after she delivers because of the risk of radiation exposure to the fetus.
  C. A positive reaction in a person who has previously received a BCG vaccine should be considered a false positive and ignored.
  D. Isoniazid should not be given to an asymptomatic person over the age of 50 because the risk of the medication is higher than the risk of developing active TB.
  E. Isoniazid daily for 9 months is the preferred treatment for most asymptomatic persons with positive TB skin tests.
  E. Isoniazid daily for 9 months is the preferred treatment for most asymptomatic persons with positive TB skin tests.

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  Explanation

  Current guidelines for TB control emphasize testing of those who are at high risk for the development of TB and who would benefit from the treatment of a latent TB infection, if detected. Based on that principle, testing is encouraged in those who are at high risk and discouraged among those who are at low risk. Further, anyone who is at high risk for the development of TB and who tests positive should be offered treatment, regardless of age. The preferred testing modality for asymptomatic persons of all ages is the intradermal (Mantoux) method of testing with PPD. Multiple puncture tests (e.g., Tine) are not sufficiently accurate and should not be used. The test should be read at 4872 hours and the diameter of induration, not redness, should be measured and recorded. Previous BCG vaccination is not a contraindication to skin testing and a positive skin reaction should be used as an indication of TB infection when the tested person is at increased risk for infection or has medical conditions that increase the risk of the disease. Delayed- type hypersensitivity reactions may wane over time. This is especially a problem in older individuals. Repeating a PPD placement may result in a "booster" phenomenon, in which a person who initially tests negative develops a positive reaction. This increases the overall sensitivity of the testing process. Three cutoff points for the determination of a positive test are currently in use: 5 mm of induration is used for those who are at the highest risk of disease, such as those immunosuppressed from HIV or medications, or those recently exposed to TB; 10 mm induration is used as a positive result for persons who have an increased probability of infection (such as immigrants from endemic areas), who have clinical conditions that increase the risk for TB (such as injection drug users) or who are residents or employees in high-risk settings (nursing homes, hospitals, prisons, and so on); 15 mm is used as a cutoff for those who Ignoring the amount of redness and using only induration as the criteria for have no known risk factors.

  positive or negative, the nursing home resident (option B) is the only one with a positive test. All persons who test positive by a skin test should then have a chest x-ray to evaluate for evidence of pulmonary TB. In an asymptomatic person, sputum studies are not necessary to determine the need for treatment. Pregnant women should still get a chest x-ray, with appropriate abdominal shielding, as soon as feasible. As stated above, a history of BCG vaccination should not deter from the need for further evaluation and treatment of a positive test result. Age should also not be a determining factor in treating someone who is at risk for the development of TB. Currently, there are four acceptable treatment recommendations for latent TB infections. Daily isoniazid for 9 months is the most widely used regimen and has the highest level of recommendation because of its effectiveness, relative safety, ease of administration, and low cost. Twice-weekly isoniazid may also be used but should only be given as directly observed therapy, due to the fact that a missed dose of this regimen represents a substantial risk of under treatment. Rifampin alone or rifampin plus pyrazinamide are alternative regimens for use in certain, specified situations.

• Question 128:

  A 72-year-old man with a diagnosis of prostate cancer was recently seen in the clinic for restaging and re- evaluation. His bone scan showed development of widespread osseous metastases and his PSA was rising. He was started on leuprolide acetate, a gonadotropin releasing-hormone (GnRH) agonist. He now returns to the clinic complaining of new severe mid-thoracic back pain, which is worse with recumbency and worse with Valsalva maneuver. He also reports that he has a brief but intense electric shock sensation in his lower extremities when he bends over to tie his shoes. On physical exam, he had localized tenderness over the mid-thoracic spine, but his motor strength, sensation, and deep tendon reflexes are all intact.

  What is the most appropriate next step?

  A. Obtain an MRI of the thoracic spine.
  B. Refer for neurosurgical evaluation.
  C. Initiate radiation therapy to the affected thoracic spine.
  D. Start the patient on scheduled narcotics for relief of the back pain and follow up in 1 week.
  E. Stop the leuprolide and schedule the patient to return to clinic in 1 week for re-evaluation.
  A. Obtain an MRI of the thoracic spine.

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  Explanation

  The patient has symptoms of spinal cord compression and needs an urgent MRI to establish the diagnosis. Spinal cord compression usually develops when patients have metastases to the vertebral body with epidural extension of the tumor, displacing the underlying thecal sac, and causing cord edema and injury. Patients with cord compression usually experience new or worsening pain symptoms days or weeks before the development of motor weakness below the level of compression. Loss of sensation and loss of bowel or bladder control occur even later. Clues that the pain symptoms may represent cord injury include pain that is worse with recumbency or Valsalva and the occurrence of Lhermitte's sign, an electric sensation down the back and into the extremities with extension or flexion of the neck or spine.

  Initiation of therapy, such as radiation therapy or neurosurgical intervention, might be necessary later but would be premature before the diagnosis is established with an imaging study. If the patient's history or physical exam suggests spinal cord compression, initiation of corticosteroids should be started immediately while diagnostic imaging is pending. Pain control with adequate narcotic analgesia is important and may be instituted while the appropriate diagnostic studies are being obtained. Delay of 1 week would be inappropriate due to the urgent nature of the problem and risk of neurological compromise. The patient's neurological status at the time of diagnosis is the most important prognostic factor: 7580% of patients who are ambulatory at the time of diagnosis will retain locomotion. But, if already paraplegic, only 10% will regain the ability to walk. While this patient appeared neurologically intact, the development of neurological deficits can progress over a period of days, making rapid diagnosis and institution of appropriate therapy such as corticosteroids and radiotherapy an urgent consideration. Other factors such as age, presence of co-morbid medical conditions, functional status, and tumor androgensensitivity are important to the patient's overall cancer prognosis.

• Question 129:

  A recent study compared two drugs--exemestane and tamoxifen--for the treatment of estrogenreceptor positive breast cancer in postmenopausal women. At the end of the study, 91.5% of the women treated with the drug exemestane and 86.8% of the women treated with tamoxifen were disease free (P < 0.001).

  What is the number needed to treat (NNT) with exemestane compared to tamoxifen to prevent one breast cancer recurrence?

  A. 79
  B. 50
  C. 36
  D. 21
  E. 14
  D. 21

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  Explanation

  Explanations:

  Relative risk is the percentage of subjects who achieve an outcome in one experimental group divided by the percentage of subjects who achieve the same outcome in another group. This statistic is used frequently in placebo-controlled trials, where the comparison occurs between the experimental group and the control group. In the study referenced in this set of questions, the comparison is between two groups who were given two different active medications exemestane and tamoxifen. The outcome studied here is the development of recurrent breast cancer. The data presented state that after the course of treatment, 91.5% of the women in the exemestane group and 86.8% of the women in the tamoxifen group were disease free. Therefore, 8.5% in the exemestane group and 13.2% in the tamoxifen group developed the outcome of recurrent breast cancer. The relative risk is then calculated as 0.085/0.132 = 0.64 = 64%. The relative risk reduction is the percentage by which the risk in one group has been reduced when compared to the other group. In other words, if the rate of an outcome in one group is 100%, the relative risk reduction is the difference between 100% and the measured relative risk. It is calculated by the formula:

  Relative risk reduction = 1 - relative risk In this example, the relative risk reduction is 1 - 0.64 = 0.36 = 36%.

  The ARR, also known as the risk difference, is calculated by subtracting the percentage of subjects who achieve an outcome in one group from the percentage who achieve the outcome in another. In this study, the ARR for those in the exemestane group compared to those in the tamoxifen group is 13.2% - 8.5% = 4.7%. The NNT is the number of subjects who need to receive an intervention (such as a medication) in order for one of them to have a beneficial outcome. In this study, the beneficial outcome would be one less case of recurrent breast cancer. The NNT is calculated as 1/ARR. In this case, the NNT = 1/0.047 = 21. In other words, 21 women need to be treated with exemestane in order for there to be one fewer case of recurrent breast cancer compared to women treated with tamoxifen.

• Question 130:

  A 19-year-old (G2P1001) female at 354/7 weeks EGA presents for a routine prenatal visit. Her pregnancy has been uncomplicated. She reports good fetal movement and denies vaginal bleeding, loss of fluid, or contractions. She is excited about the arrival of her baby and is planning to breast-feed. Her past medical history is significant for chlamydia that was treated approximately 1 year ago. She is otherwise healthy. Her blood pressure today is 110/60. Fundal height is appropriate. UA is negative.

  The patient wants to know what complications she might experience from breast-feeding. You tell her that the most common complication of breast-feeding is mastitis. If she were to develop mastitis, which of the following treatments would be recommended?

  A. dicloxacillin by mouth plus discontinuation of breast-feeding
  B. discontinuation of breast-feeding only
  C. Flagyl by mouth plus discontinuation of breast-feeding
  D. dicloxacillin by mouth with continued breast-feeding
  E. no treatment is required for mastitis
  D. dicloxacillin by mouth with continued breast-feeding

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  Explanation

  The patient would be best served by a progesterone-only pill as it will be less likely to interfere with breast milk production. The rhythm method cannot be reliably used in the early postpartum period as normal menstrual cycles may not have resumed. An IUD would be contraindicated in this patient because of her recent history of chlamydia infection. Patients may not ovulate during breastfeeding but should not rely on breast-feeding alone as a form of contraception, as pregnancy can occur while breast- feeding.

  Mastitis is a common complication of breast-feeding. It is characterized by fever, myalgias, and redness with pain in the affected breast. Antibiotic options include penicillin V, ampicillin, or dicloxacillin. Studies show that patients may continue to breast-feed while undergoing treatment for mastitis