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

USMLE USMLE-STEP-3 Online Questions & Answers

• Question 171:

  A 49-year-old male postal worker presents to your office for the evaluation of a lesion on his left arm. The lesion started about a week ago as a red pustule but has grown and now has a thick black scab. The lesion is painless. A coworker showed the patient a similar appearing lesion that she developed on her arm for which her doctor prescribed an oral antibiotic. Examination reveals a 5 cm circular black eschar with some surrounding vesicles. A Gram stain of fluid drained from a vesicle reveals chains of gram-positive bacilli.

  What organism is most likely responsible for this lesion?

  A. methicillin-resistant Staphylococcus aureus
  B. smallpox virus
  C. Clostridium tetani
  D. Bacillus anthracis
  E. group A beta-hemolytic Streptococcus
  D. Bacillus anthracis

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  Explanation

  B. anthracis causes three diseases in humans: cutaneous, inhalation, and gastrointestinal anthrax. Cutaneous anthrax is the most common of the naturally occurring anthrax diseases. The spores of the gram-positive bacillus can survive for years in soil. The disease cutaneous anthrax occurs when the spores contaminate a wound on the skin of the victim and then start to grow. This disease occurs most commonly in agricultural areas where the soil becomes contaminated by the presence of animals. Initially

  a painless papule develops, followed by vesicles which then ulcerate and a black eschar forms. In the setting of cutaneous anthrax in a postal worker who has a coworker with an apparently similar disease, bioterrorism must be suspected. This type of attack occurred in the Fall of 2001, when anthrax spores were sent through the U.S. Postal system and over 20 persons were infected. In this setting, the most appropriate initial management is to immediately contact the appropriate Public Health Authorities,

  usually the local or state health department. Appropriate treatment will also need to be instituted, under the guidance of the public health specialists, as untreated cutaneous anthrax may carry a 20% mortality rate. Antibiotic therapy would usually be with ciprofloxacin, penicillin, or doxycycline. Anthrax does not spread from person to person, so quarantine is not necessary. Inhalation anthrax is caused by the direct inhalation of spores into the lungs and gastrointestinal anthrax, the least common of the anthrax

  syndromes, is caused by ingestion. Smallpox does not occur naturally anywhere in the world. Therefore, any suspicion of smallpox must be assumed to be a bioterror event and must be reported immediately to public health officials. Physicians should be able to recognize the signs and symptoms of smallpox and be able to distinguish them from the common occurrence of chickenpox. Chickenpox lesions tend to occur in clusters and evolve asynchronously. They are often described as "dew drops on a rose

  petal" as they are vesicles occurring on an erythematous base. The lesions tend to start on the trunk and rapidly spread outward. The rash will be associated with a fever but there are usually few to no prodromal symptoms. Because of the asynchronous growth and outbreaks, a patient will typically have lesions in different stages of evolution. In contrast, smallpox lesions tend to occur synchronously and the lesions tend to be uniform. The rash frequently occurs on the palms and soles. It typically starts on the

  face and arms and then spreads to the trunk and legs. The development of the rash tends to be slower than that of chickenpox. There is often a dramatic prodrome of high fever, malaise, headache, and backache for 24 days prior to the onset of the rash. Smallpox carries an approximately 30% mortality, while mortality associated with chickenpox is very low.

• Question 172:

  A 45-year-old woman presents with a slowly growing mass near the right jaw. You palpate a firm nodule in the parotid gland but find no adenopathy and no other abnormality on examination. A biopsy reveals both epithelial and stromal elements.

  What is the appropriate treatment for this lesion?

  A. observation, as this is a benign lesion
  B. external beam radiation therapy
  C. excision with narrow margins
  D. excision with a wide margin of normal tissue
  E. chemotherapy
  D. excision with a wide margin of normal tissue

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  Explanation

  Pleomorphic adenoma (mixed tumor) is the most common tumor of the salivary glands. Pleomorphic adenoma is a benign neoplasm characterized by a mixture of epithelium and stromal elements. Two- thirds of all tumors of the major salivary glands and about half of those in the minor ones are pleomorphic adenomas. The tumor is nine times more frequent in the parotid than in the submandibular gland and usually arises in the superficial lobe of the parotid. It occurs most often in the middleaged people and shows a female preponderance. While it is a benign tumor, the recommended treatment is removal, as it will continue to grow and cause symptoms. Most authorities recommend wide local excisions, in an effort to reduce the risk of recurrence.

• Question 173:

  A 56-year-old man comes to the hospital. For the past 5 days he has had colicky abdominal pain, vomiting, abdominal distention, and constipation

  During definitive surgical treatment of the lesion shown on the barium enema, the left ureter is accidentally transected at the level of the pelvic brim. What is the most appropriate management of this complication?

  A. ureteroneocystostomy
  B. left to right ureteroureterostomy
  C. anastomosis of the two cut ends over a "double J" stent
  D. nephrectomy
  E. ligation of the transected ends
  C. anastomosis of the two cut ends over a "double J" stent

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  Explanation

  This patient presents with classic symptoms of a bowel obstruction. The diagnosis is often made by a thorough history and physical examination. Following the initial evaluation, an acute abdominal x-ray series should be obtained, which includes supine and erect views of the abdomen. The diagnosis is confirmed with the presence of dilated loops of bowel with the presence of air-fluid levels. These plain films may also suggest the location of the obstruction (small vs. large intestine). Abdominal ultrasonography has limited role in the diagnosis or management of intestinal obstruction. Serum electrolyte determination helps in identifying the electrolyte disturbances that have taken place. Fluid loss needs to be corrected with rehydration, and nasogastric suction helps in decreasing abdominal distention. Upper GI endoscopy would increase distention, and is contraindicated. Antiemetics should not be given until a definitive diagnosis is made, and then only if indicated; promotility agents have little to no role in the management of a patient with bowel obstruction, and may even be contraindicated.

  An annular constricting lesion with overhanging edges is typical of annular carcinoma of the colon. Mechanical small bowel obstruction results in multiple air-fluid levels in distended small bowel loops. Intussusception produces a "corkscrew" appearance on barium enema, and sigmoid volvulus produces a "bird's beak" appearance. In diverticulitis, extravasation of barium outside the lumen of the colon typically is seen.

• Question 174:

  A23-year-old female presents to her obstetrician gynecologist (OB/GYN) complaining of inability to conceive. She has regular menstrual cycles, and her husband's semen analysis is normal. She undergoes a hysterosalpingogram that shows evidence of bilateral distal tubal obstruction. Which of the following is the most likely cause of acquired tubal damage?

  A. appendicitis
  B. pelvic inflammatory disease (PID)
  C. salpingitis isthmica nodosa (SIN)
  D. Asherman's syndrome
  E. ruptured ovarian cyst
  B. pelvic inflammatory disease (PID)

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  Explanation

  PID is the most common cause of Fallopian tube damage. It is a polymicrobial infection that originates from upward spread of infecting organisms through the cervix and into the uterus, Fallopian tubes, or peritoneal cavity. The two most common pathogens are Neisseria gonorrhea and Chlamydia trachomatis; however, microorganisms that comprise the vaginal flora (e.g., anaerobes, Gardnerella vaginalis, Haemophilus influenzae, enteric gram-negative rods, and Streptococcus agalactiae) also have been associated with PID. Symptoms of PID include lower abdominal pain, dyspareunia, fever, back pain, and vomiting, as well as symptoms of lower genital tract infection such as abnormal vaginal discharge or bleeding, itching, and odor. In some women, symptoms are mild or even absent. Risk factors for PID include the presence of a sexually transmitted infection, a previous episode of PID, sexual intercourse at an early age, high number of sexual partners, and alcohol use. Empiric treatment of PID should be initiated in sexually active young women and other women at risk for STDs if they are experiencing pelvic or lower abdominal pain, if no cause for the illness other than PID can be identified, and if one or more of the following minimum criteria are present on pelvic examination:

  cervical motion tenderness OR uterine tenderness OR adnexal tenderness. Other common causes of acquired tubal damage include endometriosis, previous pelvic surgery, and a ruptured appendix.

• Question 175:

  An autopsy was performed following the death of a 72-year-old man. The kidney is shown in Figure below. Which of the following clinical scenarios is most likely to explain the changes seen in this kidney?

  

  A. complete urinary outflow obstruction from an enlarged prostate
  B. renal infarct from an embolism originating in the atrium of the heart due to atrial fibrillation
  C. long-standing hypertension
  D. renal cell carcinoma
  E. chronic abuse of analgesics and nonsteroidal anti-inflammatory drugs
  A. complete urinary outflow obstruction from an enlarged prostate

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  Explanation

  The photograph that accompanies the question demonstrates severe hydronephrosis, which is due to obstruction of the flow of urine. The obstruction may be located at any site along the urinary outflow tract and may be partial or total, unilateral or bilateral. Because glomerular filtration may continue for some time after the development of the obstruction, the renal pelvis and calices become dilated by continued urine production. The resultant backpressure produces atrophy of the renal parenchyma with obliteration of the pyramids. The degree of hydronephrosis depends on the extent and rapidity of the obstructive process.

• Question 176:

  A 39-year-old HIV-positive male presents for routine follow-up. He is on highly active antiretroviral therapy. A CD4 count is 250/L. His vital signs are within normal limits and his examination is normal. He has a PPD placed and follows up in 48 hours. At the site of the injection you find 6 mm of induration. A CXR is normal. He has never been treated for tuberculosis or a positive PPD before.

  Which management option is most appropriate?

  A. Collect sputum samples for 3 days to send for AFB (acid fast bacilli) staining.
  B. Empirically start four-drug therapy for active tuberculosis.
  C. Empirically start isoniazid daily for 9 months.
  D. Have the patient return in 1 week for a second PPD to assess for the presence of a "booster" phenomenon; treat with isoniazid if 10 mm induration.
  E. No intervention at this time but repeat the test in 6 months.
  C. Empirically start isoniazid daily for 9 months.

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  Explanation

  Guidelines for the prevention of opportunistic infections in persons with HIV recommend institution of TMP- SMZ for P. carinii pneumonia prophylaxis when the CD4 count falls below 200 cells/L. Azithromycin or clarithromycin are recommended for M. avium complex when the CD4 count falls below 50 cells/L. All HIV- infected individuals should be tested for IgG antibody against T. gondii as soon as possible after being diagnosed with HIV infection. Counselling should also be provided regarding avoidance of exposure to sources of Toxoplasma. Ganciclovir would be recommended for CMV prophylaxis if there were a history of prior end-organ disease. In a patient with HIV, a PPD is considered positive if there is 5 mm of induration. In a patient with a normal CXR, no symptoms of active disease and no history of treatment for a prior positive PPD, the recommended treatment would be isoniazid for 9 months. In the absence of a suspicious appearing CXR or symptoms, AFB testing would be unnecessary. A booster test would also be unnecessary, as the initial test is already positive. Multidrug therapy would be indicated only for confirmed or suspected active tuberculosis.

• Question 177:

  Which of these statements is true in regard to GI hormones?

  A. Vagal activation, antral distension, and antral protein are all stimuli for gastrin release.
  B. Secretin stimulates gastrin.
  C. Secretin is released from the antrum of the stomach.
  D. Cholecystokinin (CCK) release is stimulated by fat in the duodenum and results in release of insulin by the pancreas.
  E. CCK is released by the pancreas and relaxes the sphincter of Oddi.
  A. Vagal activation, antral distension, and antral protein are all stimuli for gastrin release.

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  Explanation

  Gastrin is the humoral mediator of the gastric phase of secretion, and the release of gastrin is stimulated by antral distention, antral protein/ amino acids, and by the vagus itself. Gastrin stimlulates gastric acid secretion, promotes gut motility, and is a trophic factor for gut mucosa. Secretin is released by duodenal mucosal S cells in response to acid and promotes water and bicarbonate secretion from the pancreas. CCK is released in the gut by intestinal mucosal I cells and stimulates emptying of the gallbladder, increases bile flow, and relaxes the sphincter of Oddi. CCK has a structure very similar to gastrin.

• Question 178:

  A50-year old male presents to the office for prostate cancer screening because he saw a TV show recommending that men get tested. He has no significant medical history, takes no medications, and has no genitourinary symptoms. There is no family history of prostate cancer. What can you tell him about prostate cancer and the PSA test?

  A. PSA testing has been proven to reduce all-cause mortality in men over 50.
  B. In spite of PSA testing, the diseasespecific mortality from prostate cancer has not changed in the past 30 years.
  C. Prostate cancer is the only condition that causes an elevated PSA level.
  D. PSA testing can prevent the development of prostate cancer.
  E. PSA testing can increase the chances of detecting prostate cancer.
  E. PSA testing can increase the chances of detecting prostate cancer.

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  Explanation

  Screening for prostate cancer with the PSA test is a controversial area. Some advocate routine screening of most men over the age of 50 while others recommend selective screening or no routine screening at all. The USPSTF gives prostate cancer screening an "I" recommendation, stating that there is insufficient evidence to recommend for or against this intervention. Prostate cancer is the second most common cause of cancer death in men (behind lung cancer). PSA screening does not help to prevent prostate cancer but it does increase the likelihood of detection of prostate cancer. However, many prostate cancers are slow growing and many with prostate cancer die of other causes. PSA screening has not been shown to reduce all cause mortality. While the mortality from prostate cancer has been decreasing over the years, the reason for this is not yet clear. PSA screening may play a role in this but improvements in the treatment of prostate cancer may also be responsible. The PSA also has significant rates of false positive and false negative readings. Benign conditions such as prostatic hyperplasia or prostatitis can elevate PSA readings and prostate cancer can exist in men with normal PSA readings. Another factor that can interfere with PSA readings is the presence of medications. Finasteride and dutasteride, which are widely used in the treatment of benign prostatic hyperplasia, can lower PSA readings, even in the presence of prostate cancer. If PSA screening is chosen by the patient and his physician, selection of appropriate patients for screening is important. The presence of symptoms related to the prostate may influence one's decision to perform a PSA test. However, many prostate cancers are asymptomatic, so the absence of symptoms may not be a reason to withhold testing. Most authorities would not recommend the routine screening of men with significant comorbidities that would result in them having a life expectancy of fewer than 10 years. One of the reasons for the controversy surrounding PSA screening is the risk of harm of testing. Elevated PSA levels frequently result in further--sometimes invasive--testing and may result in the detection of cancers that may or may not have become clinically significant.

• Question 179:

  A26-year-old female with recurrent pregnancy loss undergoes a laparoscopy and hysteroscopy. She is found to have a Mlerian anomaly with a heart-shaped uterus that has two uterine horns but one common cervix.

  What is the name of the uterine anomaly?

  A. didelphic
  B. septate
  C. unicornuate
  D. bicornuate
  E. Mlerian agenesis (Mayer-Rokitansky- Kter-Hauser syndrome)
  D. bicornuate

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  Explanation

  Mlerian anomalies result from either the lack of proper fusion or resorption of the paramesonephric (Mlerian) ducts during organogenesis. Vertical abnormalities occur when the invaginating urogenital sinus--extending in a cranial direction from the introitus--and the Mlerian structures--extending caudally-- fail to canalize appropriately. Longitudinal defects occur when the two paramesonephric ducts either do not fuse appropriately or following fusion the intervening tissue is not reabsorbed completely. A didelphic uterus represents lack of fusion, and the patient has a duplicated cervix and each cervix is connected to a separate uterine horn. Aunicornuate uterus results from aplasia of one of the paramesonephric ducts so that only one cervix connecting to a single uterine horn is found. A bicornuate uterus results from failure of the paramesonephric ducts to fuse cranially resulting in a single cervix but two separate uterine horns. A septate uterus occurs when fusion is completed but reabsorption of the intervening tissue is incomplete.

• Question 180:

  A 17-year-old male presents for evaluation of shortness of breath. He has episodes where he will audibly wheeze and have chest tightness. His symptoms worsen if he tries to exercise, especially when it is cold. He has used an OTC inhaler with good relief of his symptoms, but he finds that his symptoms are worsening. He now has episodes of wheezing on a daily basis and will have nighttime wheezing and coughing, on average, five or six times a month. You suspect a diagnosis of asthma. Which of the following would confirm your suspicion of the diagnosis of asthma?

  A. presence of expiratory wheezing on examination
  B. increase in FEV1 of 15% after giving inhaled albuterol
  C. a decreased serum IgE level
  D. presence of eosinophils on a sputum sample
  E. a peak expiratory flow measurement 30% below the predicted normal value for the patient
  B. increase in FEV1 of 15% after giving inhaled albuterol

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  Explanation

  Asthma is a chronic lung disease characterized by inflammation of the airways, causing recurrent symptoms. The characteristic symptoms are wheezing, chest tightness, shortness of breath, or cough. Symptoms often worsen in the face of certain triggers, which include allergens, cold air, exercise, or other irritants. Physical examination may reveal hyperexpansion of the thorax, expiratory wheezing with a prolonged expiratory phase of respiration, and signs of allergies or atopic dermatitis. Asthma can be diagnosed by a history of episodic symptoms of airway obstruction (wheeze, dyspnea, cough, chest tightness), establishing the presence of airflow obstruction that is at least partially reversible and ruling out other causes of these symptoms/signs. Airflow obstruction can be shown by spirometry revealing an FEV1 of <80% predicted or an FEV1/forced vital capacity of <65% of the lower limit of normal. Reversibility can be shown by an FEV1 increase of 15% and at least 200 mL with the use of a short- acting beta agonist. Expiratory wheezing on examination is commonly seen in asthma but is a nonspecific finding. Many patients with asthma have elevated serum IgE levels; it is unusual to find asthma in individuals who have a low level of serum IgE. The sputum of asthmatics may contain eosinophils, Charcot-Leyden crystals, Curschmann spirals, or Creola bodies.

  However, eosinophils may also be present in the sputum of patients with other conditions such as Churg- Strauss syndrome or eosinophilic pneumonia. Peak-flow monitoring is useful for the short- and long-term monitoring of asthma patients and for exacerbation management (by aiding in the determination of exacerbation severity which directs therapeutic decision making). persistent based on the frequency of symptoms and the degree of airflow obstruction. Based on this patient's frequency of symptoms, he falls into the moderate persistent class. An often neglected diagnosis is exerciseinduced asthma which is characterized by attacks immediately following exertion and by the lack of any long- term sequelae or increase in airway reactivity.