Explanations for the 2017 Official Step 3 Practice Questions

Here are my explanations for the 2017 version of the official USMLE Step 3 free question pdf. This is a constant reader request, so enjoy my take on these 137 questions.

You can find my thoughts on preparing for Step 3 here. In short, I think the free materials and UWorld should be enough for most folks. If you want books recs, they’re in that post. If you need another question source, I haven’t tried any of them, but you can get 10% off BoardVitals if you’re interested by using code BW10.

As for this free practice exam, Blocks 1 and 2 are “Foundations of Independent Practice” (FIP). These should take up to 1 hour each. Blocks 3 and 4 are “Advanced Clinical Medicine” (ACM). These should take up to 45 minutes each. Total practice time should be no more than 3:30 if taking under test-day conditions.

Block 1

1. A – Old man with shoulder girdle pain and/or stiffness, nonspecific somatic complaints, and an elevated ESR? Polymyalgia rheumatica, a disease of exclusively old people.
2. D – This gentleman has a cold. Rhinovirus is the most common “common cold” pathogen. Another common pathogen would be coronavirus.
3. E – Dementia in the setting of multiple strokes sounds great for vascular dementia. This is especially likely given the rapid course and association with focal neuro deficits, but be aware in real life that dementing processes are not mutually exclusive.
4. A – Avascular necrosis is a common complication of the steroid therapies given for a variety of conditions including sarcoidosis.
5. C – It’s cholangitis because of the stone lodged in and obstructing the common bile duct, which is why the CBD is dilated; you would suspect this clinically before the ultrasound essentially confirmed it due to the combination of upstream liver and pancreatic issues. Only a stone in the distal CBD will affect both organs.
6. E – Isolated elevated respiratory rate in an otherwise healthy and well-oxygenated baby after a C-section is typically TTN, felt to be a result of retained lung fluid that would normally be squeezed out/resorbed during the normal birthing process.
7. C – Lots of diarrhea after being given antibiotics? Sounds like C. diff. Historically, initial therapy has been oral metronidazole. IV will work if the patient cannot tolerate PO. 2017 IDSA guidelines now suggest oral Vancomycin or Fidaxomicin as initial therapy with Flagyl remaining first-line in areas only where access to the other two is limited. This question probably needs to be updated.
8. B – C. diff is tenacious and recurrence is common. Doesn’t mean the patient did anything wrong.
9. D – The insurance company needs the admitting diagnosis to pay for the visit. They get to hear about everything, and HIPAA doesn’t apply to billing. It would be a HIPAA violation to tell anyone else, though you’d probably try to convince the patient to let you talk to the wife.
10. A – The patient is an emancipated minor (a minor living independently and responsible for her own affairs), and thus she can consent to her own care.
11. C – Benzos, like alcohol, suppress respiratory drive. That’s why they’re potentially lethal.
12. B – You want to nonjudgmentally hear about what happened from the patient in his own words in order to evaluate. I do love the truth serum idea though.
13. C – Number needed to treat (NNT) is 1/(ARR = difference in outcome). There was a 20% difference (35% vs 15%) of recurrent encephalopathy. 1/.2 = 5.
14. B – This is a well-designed study. The main problem is that EPCS is technically challenging to perform and sclerotherapy is available basically everywhere.
15. B – B is true (it’s in the table and has an itty-bitty p-value). A confidence interval including 0 (choice A) means the two options are not significantly different. Choice C is wrong because it’s conflating the p-value with the effect size.
16. E – I think the answer here is probably intuitive even if you don’t actually know why. But anyway, recall that sickle cell RBCs have a decreased lifespan, so they don’t stick around as long to accumulate glucose as normal RBCs do, which artificially lowers the A1C value.
17. C – Middle-aged female with muscle aches, proximal muscle weakness, and an elevated CK indicating muscle breakdown. The skin cracking is a description of “mechanic’s hands.”
18. E – Post-hoc subgroup analysis is a form of BS p-hacking. The more subgroups and secondary measures you decide to look at after designing your study and gathering data, the more likely it is for you to find an (often spurious) positive result.
19. E – Inguinal lymph nodes drain the genitals.
20. C – STEMI.
21. A – His party foul was cataplexy (the awkward passing out at moments of excitation) and is common in narcolepsy. Decreased sleep latency and need for frequent (but restorative) naps are also characteristic. See this adorable video.
22. D – Digoxin toxicity is common due to its narrow therapeutic window. Common features are nausea, vomiting, and abdominal pain as well as neuro complaints like dizziness, confusion, and delirium. The classic unique finding, however, is blurry yellow-tinted vision.
23. B – A patient should always be interviewed using a certified interpreter in their primary language. A family member can be helpful in an emergency but is not a substitute.
24. E – There was no significant difference in either measure.
25. E – An ultrasound is used to assess for a tappable joint effusion, particularly in order to exclude septic arthritis. Transient synovitis (aka “toxic synovitis”) is the most common cause of acute hip pain in children aged 3-10 years and is what this child likely has. It frequency occurs after a URI, and a low-grade fever is typical.
26. D – A-fib isn’t ideal, but it’s the giant pleural effusion that’s causing her SOB and hypoxia. Thoracentesis will be diagnostic and therapeutic.
27. E – Classic features of scleroderma. Skin-tightening about the mouth can complicate airway management.
28. C – You’re not done with him yet. But, he could have TB, so mask up.
29. A – Getting a culture of whatever is causing her PID seems like a good idea. If she had a focal adnexal abnormality on bimanual exam, an ultrasound to evaluate for a TOA would be a good additional step (probably should be anyway, but the culture is non-negotiable).
30. C – She has glomerulonephritis in the setting of a what looks like strep throat. Post-strep glomerulonephritis is a type III hypersensitivity, an immune-complex deposition disease that consumes complement (C3).
31. E – Lots of varying symptoms without a cause after medical workup is characteristic of somatic symptom disorder (formerly known as “somatoform disorder”). Conversion disorder is the psychiatrically-induced loss of a neurologic function.
32. C – The control group needs to have radiographs in order to prevent a systemic ascertainment bias from unintended differences in the composition of the two groups.
33. E – First-line treatment for OCD is an SSRI.
34. A – Retinal hemorrhages with white dots (Roth spots) are indicative of septic emboli seen as a result of bacterial endocarditis, supported by the drug-use history and low-grade fever.
35. D – Math.
36. D – Type A personality with low BMI and wants a laxative? Sounds like anorexia, a condition commonly associated with amenorrhea. Though to be technical, laxative abuse is a purging behavior a la bulimia.
37. C – Total monocular vision loss means the optic nerve is affected.
38. A – Acute-onset LBP and radiculopathy are typically related to a herniated disc.

Block 2

39. D – Hypocalcemia (<8) is part of the classic Ranson criteria at 48 hours used to predict pancreatitis outcomes.
40. D – You know, try to empower patients through more information and don’t commit any crimes.
41. E  – “Groin lumps” sounds like inguinal lymph nodes, which drain you know what.
42. D – Band-like dermatomal burning pain = zoster.
43. B – Workup of a positive PPD is a chest radiograph.
44. D – “Cherry red macules” are the classic finding of methanol intoxication. Note the anion-gap metabolic acidosis.
45. C – Atlantoaxial instability is a feared complication of unchecked RA. This dynamic process can result in the basilar invagination, where the dens protrudes into the foramen magnum to indent the brainstem. Ouch.
46. B – Inadvertent removal or vascular compromise of the parathyroid glands is an important complication of thyroidectomy surgery that can result in subsequent hypocalcemia. The Chvostek sign is the twitching of the facial muscles in response to tapping over the area of the facial nerve seen in the setting of hypocalcemia.
47. E – Gross ulcerated skin/lip cancer that’s rapidly invaded the deep tissues? SCC.
48. A – Postural tremor that’s improved with alcohol is classic for essential tremor, which can be exacerbated by SSRI therapy.
49. E – She has a-fib with rapid ventricular response based on the irregularly irregular rhythm and tachycardia. You don’t really need to know the murmur part to get this question correct, but remember that mitral stenosis results in a diastolic fill murmur loudest at the apex (the snap is the stenotic valve finally and dramatically opening thanks to the increased pressure). Chronic MS predisposes to a-fib due to left atrial enlargement, which stretches and deforms the conduction pathways.
50. B – Transient lactase deficiency is exactly what it sounds like: a temporary deficiency of the enzyme lactase, typically as a result of intestinal mucosal damage by an infectious, allergic, or inflammatory process. Like an episode of gastroenteritis. It resolves once the intestinal mucosa heals and restores the brush border enzymes.
51. A – Only A is true. B is the opposite (hypoxemia was less impactful). As for C, the CI for the odds ratio of lung infiltrates includes 1, meaning that it was not statistically significant (which also means that D is wrong).
52. E – Vitamin D deficiency is rampant with symptoms including fatigue, muscles aches, and depression, among others. Checking a vitamin D level is also just helpful to make sure we’re treating osteoporosis sufficiently.
53. B – Most cases of sinusitis are viral and result in mucosal swelling/edema.
54. A –The most common cause of bloody/black nipple discharge is an intraductal papilloma, which can be diagnosed via ductography. That said, in real life, ultrasound is highly user-dependent and most people would probably at least do another targeted ultrasound to try to find the lesion now that there’s new discharge. For one thing, it’s easiest to biopsy a lesion that is seen on ultrasound.
55. A – Claudication questions usually hinge on the neurogenic vs PAD angle. This one doesn’t, as it’s clear with his numerous risk factors, med list, absent hair, and symptoms. Initial workup for PAD is ABI. His having palpable pulses doesn’t mean that he doesn’t have significant disease.
56. C – The big risk of Marfan’s disease is aortic dissection. Marfan patients often have a so-called “Tulip-bulb” annuloaortic ectasia that predisposes them to Stanford Type A (ascending) dissections involving the aortic root, which are particularly dangerous and require surgical correction.
57. D –They’ve purposefully loaded this one up, but the important diagnosis to exclude would be meningitis, hence the stiff neck. The nonspecific Lhermitte’s sign (the electric shock with neck flexion) is actually classically associated with multiple sclerosis in addition to a host of other spinal cord irritants.
58. C – One of those great most likely questions. While PCP/PJP is the classic disease-defining pneumonia of AIDS, the most common PNA in people with HIV is strep pneumo, just like everyone else. Additionally, PJP and TB both typically have a more indolent course.
59. D – Liver disease was a contraindication in the drug ad (red box at the end), and the patient has cirrhosis.
60. D – The ad shows that all three doses were similar vs placebo. Remember, when in doubt, the exam loves to test the difference between measurable differences (or even statistical significance) and clinical significance. 
61. A – Tall hairless infertile man = Klinefelter’s. 47 XXY, so you need a karyotype to confirm.
62. E – Fever + flank pain + UTI = Pyelonephritis. No further workup is needed for a woman’s first episode of pyelo, despite common ER practice. If she fails treatment, then she’ll need imaging.
63. B – Heat stroke. Most people don’t have this problem after playing for a few hours at 95 degrees, but people with CF don’t have well-functioning sweat glands, as you might recall, so they can’t cool efficiently.
64. D – The constellation of PCOS is the teenage nightmare of being overweight, hairy, and pimpled (and infertile).
65. E – He has hyponatremia. We’re not given a lot of info on volume status but no signs of hypervolemia or hypovolemia are given, so it would be reasonable to posit euvolemia. The urine sodium concentration will let us know if he has SIADH, a condition with many causes including various lung conditions (like cancer). If you’ll recall, ADH’s function is to retain free water, so SIADH results in the inappropriate excretion of concentrated urine despite hyponatremia.
66. A – Middle-school reading test.
67. A – NNT = 1 / ARR (absolute risk reduction). 1 / (65/262) = 4.
68. B – IV drug use most commonly affects the tricuspid valve with endocarditis often resulting in TR. The pan-systolic murmur of TR classically increases in intensity with deep inspiration due to increased blood return to the right heart from the systemic circulation. Conversely, a mitral regurg murmur becomes louder during expiration.
69. D – We don’t want to use latex rubber in people with latex allergies.
70. E – The splenic flexure is quite close to the spleen, which has a tendency to bleed. A lot.
71. D – Power is 1 minus the type II error (aka the false negative threshold)
72. B – The capsular ligaments help stabilize the glenohumeral joint. Unlike the hip, which has a relatively deep acetabular fossa, the glenoid fossa is shallow and so the capsule and its attachments are the prime stabilizing forces of the glenohumeral joint. One injury will predispose to re-injury.
73. C – The p-value column only demonstrates one significant value: HIV co-infection.
74. B – The patient has made an advanced directive while in no acute distress and has reiterated her desire to stick with it. We should respect that. The patient herself is able to rescind her AD at any time, whether currently with decision-making capacity or not, but her daughter doesn’t get to make that call.
75. D – Sounds like the patient is behaving like a prototypical American. A family meeting would be appropriate because family meetings are basically always appropriate. Legal guardianship for liking fast food and cigarettes is absurd, Down syndrome or not.
76. D – The co-pay is mandatory if you bill insurance. It really is billing fraud if you try to waive it. On a related note, you also can’t advertise care or procedures as “free” just because they are completely covered by insurance. That’s also deceptive.
77. C – On Heparin, loses platelets. HIT results from an autoantibody that activates and consumes platelets. This increases the risk of thrombosis, so consider HIT a thrombotic thrombocytopenic state, hence the rapid graft failure in this patient.

Block 3

78. A – Not just pharyngitis or even tonsillitis, the swollen oozing tonsil displacing the palate and uvula and resulting in trismus suggests a peritonsillar abscess, which requires drainage.
79. E – Mobitz type 1 block is the benign form of second-degree AV block. No treatment necessary unless it progresses.
80. A – Anything that turns black isn’t coming back. He has necrosis/gangrene of the forefoot and now it’s infected. “Source control” is the answer.
81. B –Condyloma acuminatum (genital warts) can be treated with imiquimod, a topic immune-response modifier.
82. E – Mild genu varum in a child 2 years of age or younger is essentially a normal variant and requires no treatment; it will self-resolve with growth. If bow-leggedness persists or worsens, bracing and eventually surgery may be needed.
83. C – He’s hypoxic. ABCs.
84. D – She’s in renal failure, yes, but is also super hyponatremic. Profound hyponatremia can result in confusion, seizures, coma, and even death.
85. B – This question is actually straight-up bad. There are multiple societal players and guidelines, which complicates things, but the move over the past decade has been to try to biopsy fewer lesions because we’re dramatically overdiagnosing and overtreating thyroid cancer. Basically, a 1 cm nodule should really only be biopsied if it has concerning ultrasound characteristics like microcalcifications. Just saying it’s solid doesn’t really count. The alternative to FNA is observation though, so at least A, C, and D are unworkable.
86. C – Unstable SVT with hypotension should be cardioverted. Alternative choices (not offered) in a stable patient would be vagal maneuvers, carotid sinus massage, or adenosine.
87. A – Fluctuance = abscess. Abscesses get drained (by a med student).
88. E – When a patient with a chest tube who is doing better is suddenly not doing better, a malpositioned or clogged tube should be an immediate consideration. The air leak has stopped because the tube is no longer absorbing said air, and the decreased breath sounds imply that the lung has likely recollapsed due to PTX reexpansion.
89. B – Classic. I see the egg-allergy question on my flu-vaccine questionnaire at the hospital every year.
90. B – Papilledema (blurring of the optic disc margins) suggests elevated intracranial pressure. While this could be related to idiopathic intracranial hypertension (which is more common in women), we need to rule out a space-occupying lesion. CT (or MRI) is the next step.
91. C – Smoking is by far the worst modifiable risk factor of all time.
92. B – MDD is treated first-line with SSRIs. He has complicated depression (with hallucinations), not bipolar disorder.
93. E – Thinking psoriasis with the raised red, scaly plaques and even some nail involvement, but every rash can be treated with steroids right? (kidding not kidding) I presume the episode of joint pain is a toss out to suggest psoriatic arthritis.
94. E – Super common safe combination.
95. D – Never fight the “normal patient who just needs a high five” question.
96. D – The mainstay of “persistent” (as opposed to intermittent) asthma treatment is an inhaled corticosteroid.
97. E – A 4 cm nail is not going to pass nicely through the entire GI tract; it may not even leave the stomach, where it likely currently is (in the LUQ). But it can definitely cause problems and should be snared by EGD.
98. C – He has a Hep B infection, as evidenced by the positive Hep B surface and envelope antigens and no immunity-conferring Anti-HBs antibody. However, the lab abnormality is a mildly elevated AST (you should still recall the AST:ALT ratio of 2 commonly associated with alcohol use). So, in this case, it’s quite likely the patient has/will have an asymptomatic Hep B infection not requiring treatment. He needs to stop drinking, and we’ll see what his liver does with the Hep B on follow-up.
99. E – These are normal findings after delivery. She should get some iron though soon too.
100. A – Turner’s patients are not fertile.
101. A – She has a scapholunate disassociation, evidenced by the widened scapholunate interval. She’s going to need an orthopedist.
102. E – Do you really think a few episodes of hives require a work-up?
103. C – Pain with passive flexion is a classic exam finding of compartment syndrome. In this case, muscle breakdown (evidenced by the elevated CK) is the source of the swelling that is poised to threaten the limb.
104. D – Rifampin is meningococcal prophylaxis used for close contacts. You do not want to get meningococcal meningitis.
105. D – An adrenal mass associated with hypertension is supposed to make you think of a pheochromocytoma. This is then confirmed by the laboratory tests. You may recall the need for preoperative alpha-blockade to prevent an operative hypertensive crisis; this can be accomplished with phenoxybenzamine, a non-selective irreversible alpha-blocker.
106. C – Fixed widely-split S2 was the buzzphrase for an ASD. An echo will show the hole, the ASD jet and its current direction, and the overall cardiac function.
107. D – Left to right shunting as in a pre-Eisenmenger ASD or VSD leads to pulmonary overcirculation which eventually results in pulmonary arterial hypertension. PAH is really bad.

Block 4

108. B –The mainstays of congenital/early HIV infection prevention are ART, cesarean delivery, and not breastfeeding.
109. D – He has the four-liner description of hypovolemia. You treat hypovolemia with saline. Remember your ABCs.
110. E – Analgesia abuse nephropathy. That’s a lot of Advil.
111. D – She’s dialysis bound but lives far from the nearest hemodialysis facility. However, high-functioning patients are good candidates for at-home peritoneal dialysis.
112. A – He meets the criteria for sepsis including fever and leukocytosis with a left-shift, so he needs broad-spectrum antibiotics.
113. A – Trigeminal neuralgia is classically treated with carbamazepine.
114. D – Lovenox is the DVT prophylaxis of choice in patients with reasonable renal function. Recent knee surgery isn’t a contraindication; orthopedic surgery is a huge risk factor!
115. C – Radiofemoral delay and pulse/BP differentials between upper and lower extremities are physical exam findings of aortic coarctation. The stiff/noncompliant narrowed aorta increases afterload and results in hypertension.
116. E – Initial cervical cancer treatment is all about staging. Low stage localized disease gets surgery and higher stages get chemoradiation.
117. B – Patients with Parkison’s and other old, weak, and/or demented folks are at high-risk for aspiration. PNA in this population, particularly involving the RLL, could be aspiration pneumonia, and steps should be taken to make sure an appropriate diet plan is in place.
118. C – A strangulated hernia is an unpredictable emergency, so while it’s clearly not an emergency right now, you also don’t wait unnecessarily to fix it either.
119. A – Cat bites on Step exams classically result in infection by Pasteurella multocida. Beta-lactams work just fine, so Ampicillan would be a great choice. Amp has the benefit (unlike a fluoroquinolone) of also covering anaerobes, since most bite injuries are actually polymicrobial.
120. D – That late systolic murmur is concerning for aortic stenosis. Untreated aortic stenosis is a rapid killer of old people, especially if it’s already symptomatic.
121. A – Alcohol decreases sleep latency (falling asleep) but also dramatically decreases sleep quality including REM sleep.
122. B – Classic hemophilia is X-linked. Her father had it and definitely passed on his affected X chromosome to her, so she is 100% a carrier. She’s having a son, which means the boy has a 50% chance of having the disease.
123. A – Abscesses get drained.
124. A – Type I diabetes often presents in DKA. Massive volume depletion is the rule and volume repletion is key. The patients are also profoundly hypokalemic, even if the serum K at presentation appears normal or even high.
125. D – Typical skin infections are caused by staph and strep, but she can’t take a beta-lactam (A) and she probably shouldn’t take a macrolide (C) due to allergies. Fluoroquinolones are better for gram-negative infections. That leaves Clindamycin as an excellent and safe choice.
126. D – Cocaine can cause chest pain and even MI due to alpha-mediated coronary artery vasoconstriction and spasm. He hasn’t responded to the first line treatments of ASA, NTG, and BZD, so next up is phentolamine, an alpha-blocker that can loosen things up.
127. D – If the distal limb is ischemic and the popliteal pulse is weak in a fresh fem-pop graft, then it’s most likely that the graft has thrombosed. An angiogram is needed to evaluate as well as try to salvage it. Anything else will just delay.
128. C – Thrush is common in newborns and young infants and is almost always initially treated with topical nystatin. Difficult cases can be treated with oral (systemic) fluconazole.
129. D – He has toxo from eating cat feces in the dirt (oops). That doesn’t address the why of his pica (geophagia, in his case). I don’t know about you, but I don’t think managing dirt-eating in five-year-olds is part of most people’s practice, even in “Advanced Clinical Medicine.”
130. D – Super duper classic gout. Big angry MTP joint full of white cells but no organism (Podagra). Treatment of an acute attack would be indomethacin. Prophylaxis is allopurinol.
131. E – She has lots and lots of subcutaneous emphysema. The air came from somewhere. In the body, that’s usually the lungs.
132. D – The AAFP actually recommends a single dose of oral steroid (usually dexamethasone) in all (even mild) cases of croup to help with airway edema. Croup is viral, so no antibiotics.
133. B – This question is outdated. While sigmoid volvulus can be initially treated via colonoscopic decompression in the absence of peritoneal signs, cecal volvulus requires surgery (or potentially a decompressive cecostomy in debilitated patients unfit for surgery).
134. E – She has cerebral edema, which is the leading cause of death in DKA. Signs, in this case, were somnolence, lethargy, headache, n/v, and incontinence. Seizures, bradycardia, and eventually respiratory arrest are also bad news. Mannitol decreases ICP.
135. D – Back pain is a way of life for the morbidly obese.
136. A – She has somatic manifestations of a targeted anxiety disorder/phobia. This would best be treated with CBT.
137. E – IV metroprolol is great for rate-control. It even worked already during this admission; it just doesn’t last very long. Rapid onset, short duration. He’ll need continued IV rate control until oral meds (or other therapy) can treat his RVR or it resolves on its own.

Whew. That’s that. Questions/thoughts are welcome in the comments as always.