Explanations for the 2013-2014 Official Step 2 CK Practice Questions

The NBME graciously provides brief practice materials for its USMLE tests, including pdf and software versions. While answers are included, there haven’t been explanations available online (until now).

If you haven’t taken a moment recently to think about how you approach Step-style questions, I might refer you to my discussion of that particular topic, particularly the section on “dealing with irritating clinical science questions” near the end. For general information on how to study for the USMLE Step 2 CK (as well as some free Step 2 resources), I recommend you read this.

From the 2014 official “Step 2 CK content description and general information” booklet (official link is dead, that’s the Archive.org cache version), I’ve listed each question and its answer with a succinct (grossly simplified) take-home message:

The newest set of official questions (2014-2015) has been released. There are only three new questions, but the question order has been entirely changed. My updated explanations can be found here.

Block 1

  1. F – Premature babies get neonatal respiratory distress syndrome due to surfactant deficiency.
  2. C – Follow your ABCs. Tachycardia and hypotension mean severe volume loss necessitating aggressive intravenous fluid resuscitation.
  3. A – Stable patients who suffer blunt abdominal trauma get CT scans when stable. Contrast is needed to assess for solid organ injury (e.g. kidneys)
  4. F – TTP always seems like too many disparate symptoms but just remember the pentad: thrombocytopenia, microangiopathic hemolytic anemia, neurologic symptoms, renal failure, and fever.
  5. D – Fever and lower abdominal pain during pregnancy equals endometritis. Infection is a major cause of PROM.
  6. D – You know what causes sudden onset headache and neck stiffness? Subarachnoid hemorrhage. The first episode can be transient, the so-called sentinel bleed before a catastrophic aneurysmal hemorrhage.
  7. B – Not fasting alters cholesterol studies, particularly serum triglycerides. You need real values prior to making any therapeutic interventions.
  8. D – Microcytic anemia is essentially always iron-deficiency unless there is a reason to suspect a thalessemia. In this case, extensive surgery has removed nutrient absorbing small bowel.
  9. B – Acutely increased sputum production in a patient with COPD equals an exacerbation, which can be treated with steroids and antibiotics. The big-time smoking history automatically implies the COPD diagnosis; the ipratropium prescription cinches it.
  10. A – The differential for chronic diarrhea in an AIDS patient includes bacterial, viral, and parasitic causes as well as HIV enteropathy. Cryptosporidium is a protozoa that classically causes watery diarrhea in AIDS patients, especially those exposed to unclean water sources (hence the traveling to Asia). CMV is a reactivation infection and MAC is ubiquitous; disease caused by either of these pathogens is due to severely depressed immunity (i.e. CD4 < 50).
  11. A – Autonomy matters. If a patient has the capacity to make medical decisions (i.e. understands the risks) and is not an imminent harm to self or others (i.e. suicidal or homicidal), then he cannot be held against his will. His control is not sufficiently poor to argue that his poor compliance is an “imminent” danger to himself. We don’t institutionalize people for noncompliance with medical treatment.
  12. D – STDs are always double-treated for both chlamydia and gonorrhea, as coinfection is extremely common, and clearance is crucial to prevent reinfection and continued spread. That means anyone with cervicitis or urethritis gets azithromycin or doxycycline with ceftriaxone.
  13. C – Remember cystic fibrosis in young people with worsening obstructive lung disease and frequent infections. The infertility is secondary to thick secretions from the defect chloride transporter, just like in the lungs and gut. Sweat chloride test makes the diagnosis.
  14. F – Vasculitides like Wegener’s granulomatosis, microscopic polyangiitis, and others causes poly-symptom disease and glomerulonephritis (hence the  hematuria and proteinuria). Positive ANCA, (either P-ANCA or C-ANCA depending on the variant) is the key laboratory finding.
  15. A – A friction rub and diffuse low-grade ST-segment elevation equals pericarditis.
  16. B – Lumbar strain doesn’t require specific treatment or workup.
  17. D – Fever, AMS, and muscle rigidity in a patient on antipsychotics (aka ‘neuroleptics’) means neuroleptic malignant syndrome (NMS). Very rare, very dangerous.
  18. A – Repetitious vomiting leads to the classic hypokalemic hypochloremic metabolic alkalosis, as well as run of the mill dehydration (hyponatremic hypovolemia). So—low sodium, low potassium, low chloride, high bicarbonate.
  19. E – Bronze diabetes and arthritis means hemochromatosis. They never say the words “bronze diabetes” on board questions, but it doesn’t mean it’s not there.
  20. F – Weight loss and worsening lung symptoms in a smoker means lung cancer. Non-small cell is by far the most common variety.
  21. B – Folic acid prevents neural tube defects. End stop.
  22. A – RUQ pain and nausea after meals equals symptomatic cholelithiasis. The test of choice is RUQ sono to assess for stones.
  23. A – Proximal muscle weakness with skin findings means dermatomyositis.
  24. B – Marfan syndrome (you know, hinted at by the familial tall stature and weak hypermobile joints) is associated with a dilated/aneurysmal aortic root, which can worsen and rupture if not monitored.
  25. B – Type II error is the possibility of producing a false negative (a negative result when it should be positive). A smaller sample size may not be able to detect a small (but real) treatment effect and thus increases the chance of type II error.
  26. D – Bartholin’s cysts get incised and drained. When recurrent, they can be marsupialized, which isn’t as fun as it sounds.
  27. A – Frequent turning prevents the development of pressure ulcers in patients with decreased mobility.
  28. A – Repeated microtrauma from repetitive stress can cause thrombosis. DVT leads to erythema and venous engorgement, the other choices do not.
  29. D – Atopic dermatitis (eczema) is the “itch that rashes.” It’s one leg of the allergic triad: asthma, allergic rhinitis, and atopic dermatitis. Treatment is with topical steroids and rigorous emollient therapy.
  30. E – An acutely swollen painful great toe means gout. Gout is an inflammatory crystalline arthropathy. Aspiration reveals white cells and negatively-birefringent needle-shaped crystals.
  31. B – Confusion and tremulousness a few days after an unexpected hospital admission on the USMLE means alcohol withdrawal.
  32. E – Intermittent polyarthritis with positive ANA (sensitive but not specific) and anti-DNA (very specific) means lupus. You don’t even need the nonpainful mouth ulcers.
  33. D – Euvolemic hyponatremia means SIADH. Both brain and lung insults are common causes. Nonphysiologic secretion is “inappropriate,” of course.
  34. E – LLQ pain with fever equals diverticulitis. The test of the choice is a CT scan of the abdomen with contrast.
  35. D – Abdominal pain is a common presenting complaint for DKA, which is a common presentation of new-onset type 1 diabetes. Note the glucose of 360.
  36. F – If it sounds like a heart attack but the patient is totally fine, it’s a panic attack.
  37. C – If all systems are constantly ramped up, it’s hyperthyroidism. Medical conditions that cause psychiatric complaints (e.g. hyperthyroidism and anxiety) are high-yield.
  38. D – If the MRI is normal, then prior traumatic hemorrhage has been ruled out. That leaves you with the vague “post-traumatic headache.”
  39. H – Chronic diffuse persistent headache without any migrainous qualities is tension headache (the most common headache disorder).
  40. B – Urinary symptoms (dysuria, urgency, frequency)  and positive urinalysis (leukocyte esterase and nitrite) without flank pain or systemic signs (fever, rigors, malaise, elevated white count) means simple acute cystitis. Add the other things, you get pyelonephritis.
  41. G – Spermicidal jelly is a never a good thing in a USMLE question. It’s either causing chemical urethritis or implying totally inadequate contraception. Here, the usual work up was totally negative.

Block 2

  1. B – Multiple lytic bony lesions equals multiple myeloma. Blastic/sclerotic lesions should make you think of metastatic prostate cancer (in men) and breast cancer (in women).
  2. G – Pleuritic chest pain and hypoxia with a normal chest x-ray should lead you to pulmonary embolism. There’s usually plenty of lung and blood flow, but it’s the mismatch that’s the issue.
  3. D – If you want to be a different gender, it’s gender identity disorder. The sexual orientation is completely separate.
  4. A – Headache and stiff neck clues you to meningitis. In a college student, that’s enough for the diagnosis. Stop reading. The treatment is ceftriaxone.
  5. A – Cough is often the only sign of asthma. Exercise-induced asthma is exercise-induced asthma.
  6. C – Macrocytic anemia with sensory changes is indicative of B12 deficiency. Causes include the classic pernicious anemia, but don’t forget the complications of GI surgery. Intrinsic factor is made by the stomach’s parietal cells.
  7. C – Increasing pain after injury and casting, particularly with passive motion, means compartment syndrome. Compartment syndrome treatment seems is barbaric, but a fasciotomy prevents neurovascular compromise.
  8. E – Abnormal vaginal bleeding in a woman over 35 requires an endometrial biopsy to rule out endometrial cancer.
  9. A – Organ donation is a complex organizational dance, and the regional procurement organization manages the nitty-gritty aspects.
  10. B – Diabetes get diabetic nephropathy. Don’t over-think things.
  11. B – The other answer choices are ridiculous. If someone seems depressed for more than two years but does not meet the criteria for major depressive disorder (MDD), it’s dysthmia.
  12. E – Don’t let the carpal tunnel history fool you. Numbness of the pinkie and half of the ring finger is ulnar entrapment (which happens at the elbow); carpal tunnel syndrome is the median nerve at the wrist (affecting thumb, index, middle, and half of the ring)
  13. E – ABCs. Patient has an airway (evidenced by breath sounds). Asymmetry implies a hemo-, pneumo-, or hemopneumothorax, which requires a chest tube immediately.
  14. D – Pain and swelling behind the ear means mastoiditis (remember the mastoid air cells?). The cause is nearly universally direct spread from otitis media.
  15. B – The patient has rhabdomyolysis from a prolonged visit with the floor. The ridiculously high CK confirms the diagnosis. Rhabo causes renal failure and requires aggressive fluid resuscitation.
  16. A – Even if you forget the signs/symptoms of Kawasaki’s disease, which you shouldn’t (strawberry tongue is a giveaway), just remember it’s essentially the diagnosis for any child with 5 days or more of fever. Treatment is aspirin (the one time it’s okay in children) and IVIG.
  17. A – It’s a cholesteatoma, which can be congenital or acquired. Even if you have no idea what that is (look it up), it’s the only answer with “proliferation” to go along with the mass. None of the others mention anything remotely mass-like.
  18. E – The only thing you do with things that look like primary melanoma is excise them completely.
  19. B – Episodic hypertension should make you think of pheochromocytoma (symptoms of headache or panic attacks etc. are common). Catecholamines are made in the adrenal medulla. The other malignancy to keep in mind with “panic-like” episodic flushing, headache, etc is carcinoid syndrome.
  20. C – Weight loss and iron deficiency anemia are concerning for colon cancer with occult blood loss. Colonoscopy is required. Parasitic causes of iron deficiency (e.g. hookworm) are first tested with stool ova & parasite screening.
  21. A – Low pH means acidemia. Renal failure causes metabolic acidosis (hence low bicarb). Low CO2 is the respiratory compensation. If it was vice versa, the pH would be high (alkalemia).
  22. C – Obstructive sleep apnea (OSA) is diagnosed exclusively by polysomnography (aka a sleep study).
  23. C – Polycystic ovarian syndrome (PCOS) is treated with estrogen-containing birth control (OCPs). Metformin would be an additional appropriate pharmacotherapy.
  24. A – Lung cavities are made by tuberculosis but filled by aspergillus (the so-called “fungus ball”)
  25. B – This man is well-controlled. Nonetheless, diabetics need monitoring for end-organ damage, specifically of the eyes, kidneys, and peripheral arteries. Diabetics should undergo annual ophthalmologic examination.
  26. D – The lungs are clear. Location, JVD, and lack of heart sounds mean cardiac tamponade from hemorrhage into the pericardium. Pericardiocentesis is the next step. Don’t forget, if you see tension pneumothorax or a water-bottle heart (from tamponade) on chest xray, you’ve already delayed life-saving therapy.
  27. B – Endometriosis is a common cause of infertility and is associated with chronic pelvic/abdominal pain and excruciating periods. Formal diagnosis is made using laparoscopy (visualization of “chocolate cysts”).
  28. C – Notice the pale, hypoperfused eyeball here. The sudden onset should have ruled out A, B, and E for you. Central retinal vein occlusion blocks the outflow of blood from the eye, leaving a bloody engorged mess. It also typically presents more gradually. Central artery occlusion is one cause of amaurosis fugax.
  29. C – If you see blood at the meatus, don’t just jam a foley into it. You can transect a damaged urethra. Get a “RUG” (retrograde urethrogram).
  30. B – A p-value less than 0.05 means that the results are statistically significant. However, most would agree that roughly 7 hours difference in cold duration is clinically insignificant.
  31. E – Genital warts don’t hurt and they turn white with vinegar (acetic acid). No systemic therapy works (although there is now a vaccine), but cryotherapy (as well as laser and electrocautery) can help. HPV will remain however, and the lesions can recur.
  32. D – Polyps over 1 cm must be biopsied. This is especially concerning considering the blood loss anemia.
  33. A – They’ve listed the criteria for ADHD. Note that conduct disorder is the kid-version of antisocial behavior. If the kid breaks rules and messes up but doesn’t seem evilthen it’s not conduct disorder.
  34. A – Sudden respiratory failure after rupture of membranes means amniotic fluid embolism (it’s not like a fat embolism; it’s actually an allergic reaction). Can happen during labor or secondary to trauma. Hypotension and coagulopathy ensue.
  35. D – Super contagious super itchy rash of the hands and fingers (especially the webs!) is scabies. Viral exanthems do not localize to the waistband and hands.
  36. B – The first imaging test in acute stroke is a noncontrast CT scan of the head. At 12 hours out, it may show ischemic strokes, but more importantly, it will diagnose hemorrhagic strokes, for which antiplatelet therapy is contraindicated.
  37. E – Exfoliative and blistering drug reactions comes in three severities of the same mechanism: erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis. Diffuse involvement (>30%) is consistent with toxic epidermal necrolysis (TEN), which carries a 30-40% mortality.
  38. D – The majority of twins are born premature, which is even more true for triplets. Only monochorionic twins experience twin-twin transfusion syndrome (as they have to share a blood supply in order for the problem to occur).
  39. B – You can usually ignore the CT scan if you want. Elevated lipase, epigastric pain radiating to the back, and alcoholism go best with pancreatitis. Varices present with hematemesis. Perforated gastric ulcers will give you free air under the diaphragm (also typically blood in the stool as well).
  40. D – They hit you over the head with hypocalcemia symptoms before giving the value. Hidden in there is the pancreatic insufficiency causing steatorrhea and fat-soluble vitamin deficiency (A, D, E, and K).
  41. A – It’s not clear that the glucose is a fasting value or not, but it’s clear the patient has insulin resistance. Diet and exercise are always necessary in DM2 and can reverse many early cases. With a 10% weight loss, for example, the patient may not require pharmacotherapy.
  42. H – The most common inherited bleeding diasthesis is von Willebrand factor (VWF) deficiency, which is doubly true in women (as hemophilias are X-linked).
  43. F – The presence of petechiae means low or grossly dysfunctional platelets (and not a factor coagulopathy). Coupled with low-grade fever, anemia (pale), splenomegaly, and lymphadenopathy, you should be thinking of leukemia (in this age group, ALL).
  44. B – Cocaine (crack or the pricier variety) causes coronary vasospasm, which can cause myocardial infarction and acute heart failure.
  45. A – Run of the mill myocardial infarction is caused by coronary artery thrombosis. Risk factors are HLD, HTN, DM, smoking, etc.

Block 3

  1. E – Everyone should get a flu vaccine. Diabetics are somewhat immune suppressed and deserve it even more.
  2. H – Recurrent infection and abscesses should raise the suspicion of chronic granulomatous disease. Suppurative arthritis does even more, if you’re likely to remember that. The real diagnosis is made from the Step 1 style question. Nitroblue tetrazolium is the test used to diagnose CGD, which is a defect in NADPH oxidase (the oxidative burst that kills Staph aureus).
  3. E – This question is comical. They even included the munchies.
  4. E – Crescents mean rapidly progressive glomerulonephritis (RPGN—bad news bears). Immune complexes along the basement membrane mean Type II, such as seen with lupus, IgA nephropathy, acute proliferative glomerulonephritis, and Henoch-Schönlein purpura. Treated with immune suppression, which in the acute phase always means steroids.
  5. A – The most common cause of hypothyroidism in developed countries is Hashimoto’s thyroiditis. In developing countries, it’s iodine deficiency.
  6. D – If environmental, food, or exposure allergies ever include shortness of breath, then carry an epi-pen.
  7. C – Meningitis/encephalitis symptoms (fever, headache, altered mental status) with monocytic predominance and only mildly elevated protein on CSF studies go along with viral meningitis, such as HSV.
  8. B – Irregular heavy menstrual bleeding in otherwise young healthy women is almost always due to anovulatory cycles. Normal pelvic ultrasound essentially rules out the rest.
  9. B – Myocardial infarction causes heart muscle death (as the name implies). Lose enough muscle and you get systolic heart failure.
  10. A – Nighttime cough and hoarseness imply laryngopharyngeal reflux (GERD that spills over into the larynx). In real life, you might try a PPI trial, but pH monitoring will confirm the diagnosis.
  11. B – Altered consciousness (intoxication, seizure, etc) predisposes to aspiration. Aspiration PNA typically goes to the RLL when upright and RUL when supine, and the damage is done by nasty GI anaerobes.
  12. C – Patients who have the capacity to make medical decisions are allowed to refuse life-saving medical treatment. You should offer it but accept her refusal.
  13. B – One of the in SIGECAPS is for suicidality. Depression is extremely common, and it’s also underdiagnosed in cancer patients.
  14. E – Thrombocytopenia without antiplatelet antibodies or splenomegaly implies a platelet production problem (e.g. myelofibrosis). The only way to know what’s happening at the factory is a bone marrow biopsy.
  15. C – He needs an antihypertensive. Diuretics like HCTZ prevent uric acid excretion and can worsen gout, so that leaves you with atenolol.
  16. B – Thick, white, and acidic means candidal vulvovaginitis (aka a yeast infection). Bacterial vaginosis typically only causes foul odor (and is alkaline, has positive whiff test, clue cells on wet mount, etc).
  17. E – Bilateral hilar adenopathy nearly always means sarcoidosis on board exams, especially in women in their 30-40s (and even more so if African-American). It’s a multisystem disease that can affect anything.
  18. D – Transillumination of a scrotal mass equals a hydrocele, which is due to a patent processus vaginalis.
  19. J – Sudden catastrophic neurological decline in patients with uncontrolled hypertension is likely due to a hemorrhagic stroke. Hypertensive hemorrhage is especially common in the basal ganglia, thalamus, pons, and cerebellum. The “hyperdense mass” is a big wad of blood.
  20. E – Of the choices listed, only X-linked agammaglobulinemia causes recurrent respiratory bacterial infections. CGD results in multiple abscess-forming infections (predominately Staph aureus). B and C also cause recurrent viral infections in addition to bacterial disease.
  21. A – Lisinopril and especially spironolactone (a K-sparing diuretic) both cause hyperkalemia. Renal failure is also a major cause of hyperkalemia, but not with the normal BUN and only mildly elevated Cr levels.
  22. D – Mitral valve stenosis is a sequela of rheumatic heart disease that can lead to LAE and left-sided heart failure if left untreated.
  23. B – Asymptomatic bacteriuria is never treated, except in pregnancy—when it should always be treated—since it’s associated with preterm labor. Treat with an oral antibiotic that covers gram negatives (like E coli), such as amoxicillin or nitrofurantoin.
  24. A – PTSD symptoms that begin within 4 weeks of a traumatic event and last 4 weeks or less is acute stress disorder (ASD).
  25. D – Unstable and hypotensive patients after blunt trauma get laparotomies (don’t put an unstable patient in the CT scanner). In addition to saline and blood products, it’s how you address the C in ABC.
  26. D – Painless uterine bleeding goes with placenta previa. Painful uterine bleeding goes with placental abruption. Ruptured vasa previa results in rapid loss of the fetus.
  27. A – Dermatomal rash means zoster. Immune insults, like chemotherapy, predispose to zoster flares.
  28. A – Lyme disease (from tick bites while hiking) can cause a Bell’s palsy.
  29. A – Totally healthy people with indirect hyperbilirubinemia means Gilbert syndrome (which causes decreased bilirubin conjugation due to reduced glucuronyltransferase activity).
  30. C – Nifedipine (a peripherally-acting CCB) can be used to treat Raynaud’s phenomenon, which is a painful vasospastic condition associated with scleroderma.
  31. E – Pseudogout (calcium pyrophosphate deposition disease) is an inflammatory arthritis with a predilection for the knee that causes synovial calcifications.
  32. E – The large cystic midline pelvic mass is her bladder, which is full of urine and must be decompressed before any further workup is pursued.
  33. D – Lack of oxygen is reducing the systolic effort of the heart. Lung pathology does not intrinsically acutely reduce systemic blood pressure.
  34. C – Anesthesia to the anterolateral thigh is the distribution of the lateral femoral cutaneous nerve. LFC neuropathy can be caused by compression near the inguinal ligament (say, from a hematoma). Note that it’s the compression of the nerve that causes decreased sensation, not the hematoma itself.
  35. D – A boot-shaped heart means Tetrology of Fallow on board exams. Outside of that giveaway, TOF is by far the most common cause of cyanotic heart disease.
  36. E – Weight gain, fatigue, and constipation go with hypothyroidism. High LDL cholesterol actually does too, but the question is doable even when ignoring the lab values.
  37. B – Two things make this aortic dissection instead of a heart attack or pulmonary embolism. First, the diastolic murmur is that of aortic insufficiency/regurgitation, which is happening because the dissection is involving the aortic root. Second, diminished femoral pulses implies that the dissection also involves the descending thoracic aorta distal to the takeoff of the brachiocephalic and left subclavian arteries (which supply the arms). Only an issue in the aorta can cause that constellation of symptoms.
  38. F – SIGECAPS+. Patient has MDD and developing panic disorder. Both of these can be treated first-line with SSRI therapy, such as paroxetine (Paxil).
  39. C – The only test that can be performed between weeks 10-12 of gestation is chorionic villus sampling (CVS). It’s too early for amniocentesis, nuchal cord translucency, or triple/quad screening.
  40. E – Working up serious hypoglycemia involves measurement of both insulin and C-peptide (the cleaved by-product of endogenous proinsulin) to assess for hyperinsulinemia and distinguish endogenous (e.g. insulinoma) from exogenous (e.g. Munchausen’s) causes.
  41. A – Most common palpable breast mass in women less than 30 is fibroadenoma. In women between 30-50, it’s a cyst (or fibrocystic changes of the breast). Greater than 50, malignancy.
  42. H – Congenital rubella is super uncommon (but very common on the boards): “blueberry muffin” rash, sensorineural deafness, eye abnormalities, and congenital heart disease. The mild rash in the mother is the historical clue.
  43. A – Delivery at home is the red flag. Neonatal tetanus comes from inadequate cord hygiene, particularly when the cord is cut with a non-sterile instrument.
  44. G – She’s Hepatitis B immune, but Hepatitis A isn’t mentioned. Hep A is transmitted through fecal-oral transmission, so when it comes to daycare, it means that if one kid gets it, they all get it.
  45. D – Dark urine and pale stools mean direct hyperbilirubinemia (i.e. not physiologic jaundice, breast feeding or breast milk jaundice, G6PD deficiency, etc). With a subhepatic mass, you’re looking at a choledochal cyst: a rare, sad, congenital abnormality of the biliary system that leads to biliary obstruction, cirrhosis, and death if untreated. Some subtypes can be treated with surgery, others eventually require a liver transplant for survival.

That’s it.

Requests for further clarifications etc can be made in the comments below.

21 Comments

  1. thanks much for this sir!

    do you know if such explanations are available for the step 1 practice questions as well? or where to find them?

    Reply
  2. I haven’t seen a recent version around. Kaplan has a kept a copy of the 2009 answers available here, but at first glance, it does look like the questions have changed a bit. They may have a newer version for their customers.

    I might get around to doing my own (but probably not in the immediate future).

    Reply
  3. thanks! i have just begun my studies and planning on taking it day or 2 before exam (next year). hope it would be available then!

    Reply
  4. thank you so much for posting. I am going to use these to help a student figure out what she is doing wrong in her test taking processes when she misses a practice question. (hopefully)

    Reply
  5. How good of correlation is this with the sample test to the real deal. I just took it and got 83% right. The questions seemed rather simple compared to uworld, so I don’t know what to think about the score.

    Reply
  6. Correlates well in my opinion. The real test definitely has a higher percentage of easy questions compared with UW. UW questions are of the same style and content but tend toward the more difficult side, which is part of what makes them such an excellent study tool.

    Reply
  7. Hi Ben, thanks for your answer explanations! I was wondering if you could elaborate on Block 2, Question 81 – the alcoholic with pancreatic insufficiency and vitamin D deficiency. This patient seems like a candidate for hyomagnesemia as well, which usually coincides with hypocalcemia and presents with similar symptoms. Any tips on how to distinguish between answers A and D?

    Reply
  8. It’s not that hypomagnesemia is unlikely; it’s common in alcoholics as well and can cause both hypocalcemia (and even the other choice, hypoparathyroidism). But, in a single best answer question, your goal is to not necessary prove that only one answer is reasonable, it’s to pick the “best” one:

    In this case, the question stem tells you about his history of pancreatitis (alcoholic admitted for “abdominal pain” on several occasions) and then tells you about his chronic symptoms of pancreatic insufficiency. Putting that together, the implication is these are related to the causes of his current hypocalcemia. While hypomagnesemia is relatively common, this is predominately an issue of poor diet and alcohol-mediated renal excretion (i.e. not a sequelae of chronic pancreatitis).

    Reply
  9. Thank you for sharing these explanations. They really help.
    Any way to explain why there is increased bicarb with hypokalemic, hopochloremic met alkalosis? Shouldn’t the bicarb decrease to compensate for the loss of chloride?

    Reply
  10. The primary driver is the need to supply a hydrogen ion H+ for HCl in new gastric acid, which creates a backtide of bicarbonate. Renal mechanisms will then rapidly correct this in the absence of continued vomiting.

    Reply
  11. This is wonderful! Thank you so much! It seems the USMLE has updated the test since your post. I think they reused some of the questions, since I had the same question about why one of my answer choices was incorrect (i.e. hypomagnesium causing hypocalcemia in alcoholics) but it’s a different question number on the test I took. Here is the link for the updated test.

    http://www.usmle.org/pdfs/step-2-ck/2014_Step2CK_SampleItems.pdf

    Reply
  12. Yes, they released an updated set later in the year, so in effect these are the 2013-14 explanations. The set you’ve linked to is the 2014-15. They tend to reuse a lot of questions; I haven’t compared the sets like I did for the Step 1 materials yet, but around half of those were reused during the last update.

    Reply
  13. Yup, just by using the “find a word” feature, I’ve been able to find your explanations to over half of the questions! Do you have an idea of how I could correlate my percent score to the 3-digit NBME score?

    Reply
  14. There was a calculator online for the Free 150 to Step 1, but I don’t think anyone has ever accumulated enough people to do the same for the Step 2 CK questions. There’s no way to really know, and the changes each year to the set would change the relative final score. If I had to somewhat arbitrarily venture a guess, I’d suppose that 80% correct is somewhere around 230 (with 70% around 200 and 90% closer to 250).

    Reply
  15. For those wondering, the explanations for the updated 2014-15 set can be found here. Overall, there were only three new questions (but the order is completely jumbled).

    Reply

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