USMLE Step 3

Explanations to Released Items

Every fall, the NBME releases sample questions for candidates to see what USMLE Step 1, 2 and 3 questions look like. The items are published on CD-ROM; they also can be downloaded from the USMLE web site. It is important for you to review these items, as they are similar in both format and content to those on the real exam. The Step 3 CD-ROM also contains five cases in the CCS format for you to practice with before test day.

What the NBME doesn't provide are the explanations. That's where we offer you our USMLE preparation courses! We have written comprehensive explanations to all multiple choice items, including discussions of why the right answers are right and why all the distracters are wrong. Please note that the questions themselves are copyrighted by the NBME and cannot be reproduced. If you don't already have the USMLE's CD-ROM, visit www.usmle.org.

Sample Questions and Explanations

Question 1

1. A 31-year-old obese female with a history of asthma comes to your office complaining of severe shortness of breath and wheezing. She produces from her purse a number of active medications including a beclomethasone metered dose inhaler (MDI) and salmeterol MDI. She also appears to be taking zafirlukast daily. She tells you that she has been hospitalized many times for asthma flares and was once intubated. Her review of systems is pertinent for asthma attacks of increasing severity over the past few weeks but she denies any fever, cough, chills, or pleuritic chest pain. On exam, the patient demonstrates audible expiratory wheezes with a markedly prolonged expiratory time. Her respiratory rate is 20-24/min and she is acutely short of breath, using accessory muscles of respiration to breathe. Her vital signs are otherwise stable. Which of the following is the most beneficial management of this patient?

(A)	Obtain a chest radiograph to rule out pneumonia
(B)	Obtain a peak flow estimate
(C)	Albuterol nebulizer therapy in the office
(D)	Refer the patient to the local hospital for admission
(E)	Refer the patient to the local emergency room for evaluation and treatment

Explanations Question 1

The correct answer is E. A patient with severe asthma who has had multiple previous admissions for asthma must be treated emergently. Although she presented in an office setting, simply managing her current flare in an outpatient setting is not sufficient, as these patients tend to decompensate rapidly. She is already in mild-to-moderate respiratory distress and will only get worse if appropriate therapy is not initiated. If she worsens, the office setting is no place to manage her.

Getting a chest radiograph to rule out pneumonia (choice A) would be acceptable if this patient's condition were not acute. Since the overriding concern is for impending respiratory collapse, she should be triaged to a local ER and have a chest radiograph taken under more controlled conditions.

Documenting a peak flow estimate (choice B) is not going to alter any management decisions. Even if her flows were not markedly depressed, she is still in moderate respiratory distress and is not moving air well.

Initiating albuterol nebulizer therapy (choice C) may be beneficial, and if the therapy is successful, the acuity of the situation has passed. However, if the therapy fails to be effective, then valuable time has been lost and the patient's condition will likely be more critical.

The ulnar nerve (choice E) crosses the elbow posterior to the medial epicondyle of the humerus. It then passes between the two heads of the flexor carpi ulnaris and courses through the forearm deep to this muscle.

Referring the patient to the local hospital for admission (choice D) is not equivalent to having her seen and evaluated in the emergency room. Given that this patient is in near extremus, she requires evaluation and therapy by the ER team.

Question 2

2. A 69-year-old man is brought to the clinic for progressively worsening memory loss and confusion. The patient has a long history of hypertension and coronary artery disease. He has not seen a physician in a number of years and has not been taking any medications. The family reports a step-wise decline in his cognitive function over the past few years. He has long periods where he appears stable and then suddenly worsens over a few days. On physical examination, he is a thin but not cachectic appearing man with a blood pressure of 185/110 mm Hg. His physical examination is notable for a faint carotid pulsation on the left with a prominent right carotid bruit. He has an S4 gallop on precordial examination.

Which of the following is the appropriate first step in the management of this patient?

(A)	Initiate donepazil therapy
(B)	Initiate atenolol therapy
(C)	Initiate warfarin therapy
(D)	Order a carotid ultrasound study
(E)	Order a head CT scan

Explanations Question 2

The correct answer is B. This patient suffers from a form of dementia known as multi-infarct dementia. The requirements for the diagnosis of dementia include a demonstration in the decline of memory as well as impairment of at least one other cognitive function (aphasia, apraxia, agnosia, executive planning). Multi-infarct dementia is the second most common cause of dementia and is often due to severe carotid disease or embolic disease. This patient has a number of issues on presentation, the most urgent of which is his blood pressure. Although the management of this pressure has subtle details, the best course of management from all of the choices given is to initiate atenolol

Donepazil therapy (choice A) is an anti-cholinesterase inhibitor used in dementia of the Alzheimer's type.

Warfarin therapy (choice C) is generally started in patients with severe carotid disease. However, this patient's most pressing issue is blood pressure control. Starting warfarin in patients with poorly-controlled hypertension predisposes them to catastrophic hypertensive bleeds.

Ordering a carotid ultrasound study (choice D) is a very appropriate intervention to assess the magnitude of this patient's carotid disease. However, the primary medical issue is not urgent revascularization of the carotid vasculature, but control of his severe hypertension.

Ordering a head CT scan (choice E) may be a useful diagnostic study in the evaluation of dementia, however, in a patient with multi-infarct dementia, it is not more useful that carotid studies.

Question 3

3. A 43-year-old African-American man comes to the clinic for the first time as part of a neighborhood-screening program for hypertension. He reports that he has no past medical history but has not seen a physician routinely for the past ten years. He smokes two packs of cigarettes per day but denies ethanol or any substance abuse. He takes no medicines regularly. The nurse measures his blood pressure as 165/90 mm Hg in the left arm while sitting. The physician has a long discussion with the patient concerning the possibility that his blood pressure has been elevated for some time and that he may need medical therapy in order to lower it to appropriate levels. A careful physical examination is performed looking for possible end-organ manifestations of long-standing untreated hypertension. Which of the following signs is suggestive of long standing hypertension?

(A)	S3 gallup
(B)	Abdominal bruit
(C)	Carotid bruit
(D)	S4 gallup
(E)	Systolic ejection murmur

Explanations Question 3

The correct answer is D. Hypertension effects multiple organs adversely. The heart is one of the most severely affected. As a consequence of the long-standing pressure overload on the left ventricle, the initial response of the myocardium is to hypertrophy. As the ventricle enlarges and begins to encroach upon sub-endocardial blood supply, mild ischemia and diastolic dysfunction occur. These consequences are manifest by an audible gallup during diastolic filling (atrial contraction) of a stiffened ventricle.

An S3 gallup (choice A) is the sound heard during rapid diastolic filling of diseased ventricle and results from turbulent blood flow. This is not specific for hypertensive heart disease and is not a characteristic finding.

An abdominal bruit (choice B) or carotid bruit (choice C) are sounds heard over the abdomen and neck respectively. They represent turbulent flow across an artery. The turbulence is most often caused by atheromatous plaques deposited in the arterial intima. Bruits are a sign of severe peripheral vascular disease.

A systolic ejection murmur (choice E) is heard after S1 and during the time of systolic ejection. It is usually caused by a diseased aortic valve, either stenosis or sclerosis. These conditions are not a consequence of long-standing hypertension.

Question 4

4. A 19-year-old gravida 0 presents to the student health center complaining of lower abdominal pain and urinary urgency of three days duration. She has not had this condition before. She is sexually active, and sometimes uses condoms for contraception. She has intercourse about three times a week; her last intercourse was three days ago. Her last menstrual period was three weeks ago. Her periods are regular at 28-day intervals, and last about 5 days. She does not have any gastrointestinal symptoms. Her temperature is 1010F (38.30C), pulse 100, respirations are 20/min, and her blood pressure is 100/60. On physical examination, the abdomen is soft, but there is tenderness to deep palpation in both lower quadrants with slight rebound tenderness as well. The liver, kidney, and spleen are not palpable. Bowel sounds are active. The vulva is clean; there is no evidence of discharge or irritation. The vaginal is well supported, uninflamed, and clean. The cervix is nulliparous, and there is a mucopurulent discharge in the os. A cervicovaginal PAP smear is taken. Cultures are also taken from the vagina and cervix. There is tenderness to cervical motion. The uterus is of normal size, shape and position. The adnexa are difficult to palpate, and are not well felt, but there is bilateral tenderness. Rectovaginal examination is confirmatory. Trichomonads are identified on microscopic examination of vaginal secretions. Her white blood count is 10,000 with a left shift; urinalysis shows 1-2 WBC, trichomonads, and 1+ proteinuria. Which of the following is the next best step in her management?

(A)	Admit to the hospital for parenteral antibiotic treatment
(B)	Begin 7 days of metronidazole, 500 mg TID po for the patient and her partner
(C)	Order ceftriaxone 250 mg IM and doxycyline 100 mg b.i.d. po for 10 days
(D)	Prescribe acetaminophen for pain and intermittent heat to the lower abdomen; re-evaluate when cultures return
(E)	Schedule for a transvaginal ultrasound

Explanations Question 4

The correct answer is A. The differential diagnosis in a woman with fever, lower abdominal pain, and pelvic tenderness includes pelvic inflammatory disease (PID), appendicitis, torsion of an adnexal mass, inflammatory bowel disease, and infected septic abortion or ectopic pregnancy. The history and findings in this case favor pelvis inflammatory disease. There is a paucity of gastrointestinal complaints, which more than likely rules out appendicitis and inflammatory bowel disease. Normal uterine size and menstrual history make pregnancy unlikely, but a pregnancy test in a female of reproductive age is in order. Infected ectopic pregnancy is a consideration, but unilaterality of symptoms would be expected. Torsion of adnexa also causes unilateral symptomatology. In favor of PID are the menstrual history (she is just premenstrual), poor contraceptive practice suggesting unprotected intercourse, mucopurulent cervical discharge, and tenderness to cervical motion.

This patient has trichomoniasis. She illustrates the point that patients with one STD often have others, and should be investigated for them. Metronidazole orally for seven days for both partners (choice B) is prescribes treatment for bacterial vaginosis or trichomoniasis. The priority of treatment requires that the more serious infection (PID) be treated first.

The two most important goals of medical therapy are the resolution of symptoms and preservation of tubal function. Antibiotic treatment should start soon after cultures are taken. Early diagnosis and early treatment help reduce the long-term sequelae. Inpatient therapy is prudent for patients with a temperature > 1020F (390C), for those with guarding or rebound tenderness in both lower quadrants, or patients who can not tolerate or be trusted to comply with oral therapy. Hospitalization is also recommended for all nulliparous women, those who have had an inadequate response to oral therapy, patients with HIV, all adolescents, and those with tuboovarian complex or abscess. Inpatient therapy consists of bedrest, restricted oral feedings, rehydration, and either or two regimens of intravenous antibiotic therapy: either cefoxitin or cefotetan and doxycycline; or clindamycin and gentamicin. As the infection resolves, these regimens are followed by oral doxycycline for two weeks. Therefore, ordering ceftriaxone 250 mg IM and doxycyline 100 mg BID po for 10 days (choice C) falls far short of what is required, and is not considered optimal treatment.

Delay until cultures return (choice D) increases the risk of permanent tubal damage and cannot be justified.

The first priority is to administer antibiotics parenterally in sufficient dosage to minimize serious sequelae. Then, if pelvic examination is unsatisfactory, ultrasound examination (choice E) of the pelvic viscera allows determination of the extent of infection. This is important in determining the duration of parenteral antibiotic therapy, or if medical treatment is unsatisfactory, the timing and extent of surgery.

Question 5

5. On the morning of the second day after delivering a 3,500-g infant, a 16-year old gravida 1, para 0 develops a temperature of 1010 F (38.30C). Her antepartum course was unremarkable. Membranes ruptured shortly after hospital admission and the onset of labor was spontaneous but desultory. Oxytocin augmentation was necessary. The first stage of labor was 22 hours; the second stage was 3 hours and 45 minutes. Delivery of the vertex was expedited by vacuum forceps over an intact perineum under pudendal block anesthesia. The placenta delivered spontaneously. Since delivering, she had been ambulating and eating well. Physical examination reveals a temperature of 1020F (38.80C), a pulse of 108 bpm, respirations 22/min, and a blood pressure of 110/60. Breasts are full with moderate colostrum secretion from the nipples. The abdomen is soft; there is no liver, kidney, or spleen palpable. The perineum is clean, and the lochia rubra has a foul odor. Pelvic examination is within normal limits for postpartum status except for uterine tenderness to motion and foul lochia. Examination of the extremities, including previous intravenous sites, is within normal limits. Which of the following is the next best step in her management?

(A)	Begin oral methylergonovine, encourage fluid intake, re-evaluate in four hours
(B)	Culture the lochia and start acetaminophen; await culture report
(C)	Initiate imipenem/cilastatin intravenous therapy
(D)	Order a CBC, encourage fluid intake, re-evaluate in four hours
(E)	Start a first-generation cephalosporin orally

Explanations Question 5

The correct answer is C. The patient has endometritis based on the following facts: fever, uterine tenderness, and foul lochia. The following factors predisposed this patient to infection: prolonged labor, prolonged rupture of the membranes, operative delivery, and multiple examinations. Other factors that predispose to the postpartum development of endometritis include: chorioamnionitis, toxemia, intrauterine pressure catheters (>8 hours), fetal scalp electrode monitoring, preexisting vaginitis or cervicitis, cesarean section, intrapartum and postpartum anemia, poor nutrition, obesity, low economic status, and coitus near term. The most common cause of postpartum fever is uterine infection. Extragenital infections are much less common than endometritis and urinary tract infections. Bedside history regarding coughing, chest pain, breast tenderness, leg pain, and pain at the site of the previous intravenous infusions, and a physical examination should be performed, covering these same areas of possible infection. Fever after the exclusion of other causes remains the most important criteria for the diagnosis of endometritis. The microbiology of endometritis is polymicrobial. Commonly isolated aerobes include gram-negative bacilli (e.g., E. coli) and gram-positive cocci (e.g., group B streptococci). Therefore, a broad-spectrum antibiotic should be chosen, such as imipenem/cilastin. Good results have been reported with other antibiotics, such as cefoxitin and Clindamycin/aztreonam.

The patient is not experiencing heavy bleeding, so the use of uterotonic agents such as methylergonovine (choice A) is not indicated. Since the diagnosis of endometritis is readily apparent, a re-evaluation in four hours is not indicated. Encouraging fluid intake is appropriate.

Since endometritis is polymicrobial, culture of the lochia (choice B) is unlikely to reveal unexpected bacteria, and will not change therapy. Initial therapy should not be delayed, and the choice of antibiotics is empirical. Should the patient not respond to appropriate antibiotic therapy, culture might then be indicated.

There is no suggestion that the patient is or is likely to become anemic in the immediate future. Her white blood count is expected to be elevated, so ordering a CBC (choice D) would not change the indicated plan of management.

The spectrum of first-generation cephalosporins (choice E) is not broad enough to be consistently effective. Initial administration of antibiotics should be by the intravenous route.

Vibrio cholerae (choice F) typically produces a watery, nonbloody diarrhea with flecks of mucus (rice-water stools). Abdominal pain is not a feature. Massive fluid loss and electrolyte imbalance are complications. In the U.S., cases of cholera (El Tor 01 strain) are associated with the Gulf coast and ingestion of poorly cooked or poorly stored crabs, shrimp, or oysters. A strain of V. cholerae called non-01 is also found along the Gulf coast. Patients who ingest contaminated shellfish experience fever, copious watery diarrhea, and abdominal cramps within 48 hours after eating.