Explanations for the 2014-2015 Official Step 1 Practice Questions

Using the official 2014-15 “USMLE Step 1 Sample Test Questions,” (cached version here) I’ve written explanations and take home points for each of the 138 questions (the “Free 150”). The 2015-16 set has no new questions (a few have actually been removed), so this is still current. I can’t reproduce the questions themselves of course as they’re uber-copyrighted.

An asterisk means it’s a new question (of which there are around 84). The questions and explanations for last year (2013-14) can still be found here.

The new 2016 set is out and has around 50 new questions, which are discussed here.

Block 1

1. C – Acute abdominal pain in a fertile woman is very frequently going to be an ectopic question. Associated fun fact: the most common cause of secondary amenorrhea is pregnancy.
2. E – Parents can be overly protective of their children with chronic diseases (diabetes, lupus, etc). This child doesn’t have SCID, so going to school isn’t going to kill them. The child is in overall reasonable health with only mild symptoms. Vulnerable child syndrome is characterized by unreasonable parental anxiety. *
3. B – HGPRT = high uric acid. Self-mutilating behavior (e.g. bad finger biting) is one of the more specific clinical features.
4. E – Functional parathyroid adenomas can cause elevated parathyroid hormone (PTH), which results in hypercalcemia and hypophosphatemia. Hypercalcemia is characterized by the rhyming symptoms of: stones (renal, biliary), bones (including bone pain to osteitis fibrosa cystica), groans (abdominal pain, n/v), thrones (polyuria, constipation), and psychiatric overtones (from depression to coma). *
5. B – You are seeing a tube inside of a tube in the pathology specimen. Yes, look again: bowel within bowel. Intussusception. Currant jelly stools. Classic history (sudden onset colicky pain, palpable mass). Now, a right lower quadrant lesion that causes pain and hematochezia, particularly in a child? Then you would get to think of Meckel’s (with its rule of 2′s).
6. F – While staph aureus is the most common cause of hematogenous osteomyelitis in children, Salmonella is the most frequent cause for patients with sickle cell anemia (a test favorite). I think I may have even had this fact tested twice on my Step.
7. D – Reye’s syndrome is the reason why children don’t receive aspirin (except to treat Kawasaki’s disease, of course). Reye’s syndrome is characterized by vomiting followed liver damage (hepatic steatosis and hepatomegaly) and encephalopathy beginning with irritability and aggressive behavior and potentially progressing to coma.*
8. B – Bisphosphonates work by decreasing osteoclast activity (thereby reducing bone resorption). Choice F is the opposite of how estrogen therapy works (RANKL is found on osteoblasts, and its activation triggers osteoclasts and stimulates bone resorption).*
9. B – Azotemia, hemoconcentration, and hypotension/tachycardia are all results of dehydration. This may lead to acute renal failure if allowed to continue (but this diagnosis requires a change in creatinine of 0.3).
10. A – Phenylephrine is an alpha-agonist nasal spray and oral medication that often shows up on exams. Oxymetazoline (Afrin) is a similar alpha-agonist nasal spray. Pseudoephedrine is another decongestant with a similar MOA that’s less common now that it’s a federally monitored component of methamphetamine production. Topical alpha agonist decongestants are physically addictive and can cause miserable rebound congestion (rhinitis medicamentosa). Systemic formulations can cause hypertension and worsen prostate problems by causing prostatic smooth muscle constriction. Just remember that tamsolusin (Flomax) is an alpha-5a antagonist, which relaxes prostate muscle.
11. A – She has nephrogenic diabetes insipidus (large volume dilute urine production that cannot be reversed with the administration of exogenous vasopressin). Aquaporins are the water channels that allow for the reabsorption of free water from the collecting ducts and the production of concentrated urine.
12. A – The p-value corresponds to the likelihood of a type I error (a false positive). A lower p-value means a lower acceptable likelihood of obtaining the same results by chance, and thus, significant results can be reported more confidently (a 1% false positive rate instead of a 5% rate).*
13. A – Gonorrhea can change its pilus, which is responsible for adhesion to host cells and the main antigen to which the host mounts an immune response. Neisseria gonorrhoeae is able switch out different pilin genes, and for this reason, prior infection does not confer long lasting immunity.*
14. B – Crossed findings means a brainstem lesion. Left (ipsilateral) tongue, right-sided (contralateral) weakness means the exiting left hypoglossal nerve has been affected (within the left medulla). B is the pyramid where the corticospinal tract runs to control muscles (prior to the decussation). This is known as medial medullary syndrome or Dejerine syndrome.
15. A – p53 is the quintessential tumor suppressor (it activate apoptosis). Carcinogenesis of HPV is caused by insertion of the virus into the host DNA and producing a protein which binds with an essential p53 substrate, functionally inactivating the p53 and its apoptotic cascade. C (transactivation/TAX) is how HIV and HTLV cause cancer. E (cmyc translocation) causes Burkitt lymphoma.*
16. A – Atypical antipsychotics (e.g. clozapine, quetiapine, etc) are more likely to improve negative symptoms (affective flattening, anhedonia, avolition, aphasia) when compared to typical antipsychotics (e.g. haloperidol). They are no more effective at treating positive symptoms (hallucinations, delusions). Highly testable fact.*
17. A – It’s the antibodies to surface antigens that are protective. Hemagglutinin is a surface antigen that is responsible for clumping RBCs in vitro.
18. A – All the vesicles contain the same viral infection, so all should have the same appearance on gel. Choice D is what a gel looks like without using a restriction enzyme digest (no discrete bands of specific weights).
19. E – Xanthogranulomatous pyelonephritis (XGP) is a rare form of chronic pyelonephritis, especially associated with Proteus infection. Tumor-like growth, upper urinary tract infection, and (this is key) lipid-laden foamy macrophages make this neither acute pyelo nor cancer. Malacoplakia causes GU papules/ulcers, typically of the bladder (not super important).
20. B – Post-streptococcal glomerulonephritis is caused by the deposition of circulating immune complexes (a type III hypersensitivity and a test-favorite).*
21. A – As always, it’s almost better to ignore the pictures when possible. This gentleman has a peptic ulcer, which we know is caused predominately by H. pylori infection. H. pylori produces proteases and particularly urease, which allow it to increase the pH of the its local environment by cleaving urea into ammonia, which is toxic to gastric mucosa. The picture demonstrates H pylori, which are evident with silver staining.*
22. D – Schistosomiasis is a parasitic worm particularly endemic in Africa (Egypt in particular comes up a lot on questions) that is most associated with chronic cystitis. Calcifications of the bladder wall are essentially pathognomonic. Chronic infection is associated with an increased risk of squamous cell carcinoma of the bladder (as opposed to the usual urothelial/transitional cell).*
23. E – This patient has chronic kidney disease, as indicated by elevated serum creatinine/BUN and evidence of anemia of chronic disease (normochromic normocytic). Poorly functioning kidneys do not hydroxylate 25-Dihydroxycholecalciferol to 1,25-Dihydroxycholecalciferol well nor produce adequate erythropoietin (hence the CKD-related anemia). Patient’s with CKD development thus develop secondary hyperparathyroidism due derangements in phosphate excretion and inadequate Vitamin D activation resulting in hypocalcemia.  Thus, we should expect to see low calcium, high phosphorus, low 1,25 vitamin D, and low Epo, which is E.*
24. C – Isoniazid can cause peripheral neuropathy due to its depletion of pyridoxine (vitamin B6). B6 supplementation is therefore preventative. INH can also cause drug-induced lupus (another test favorite) and sometimes severe liver disease (also fair game).*
25. C – The meningitis diagnosis is a giveaway. Your job is to know two things: 1) the common pathologic organisms in different age groups or 2) that Neisseria is a gram negative diplococcus.
26. B – To amplify tiny fragments of DNA in order to detect their presence, we use PCR. The question is a description of the process. Southern Blots are used to detect a specific DNA sequence within a DNA sample.*
27. C – Hookworm infection can cause intestinal irritation leading to chronic GI blood loss and iron deficiency anemia. An otherwise healthy boy who lives in rural Mississippi, probably playing in the mud in his bare feet like a hillbilly? That’s the kind of kid who would get hookworm. Treatment is mebendazole (albendazole would also be fine. These are your go to choices for anti-helminthics).*
28. A – Androgen insensitivity is caused by a defective androgen receptor. DHT is responsible for creating male genitalia during fetal sexual development. The default human gender is female. So a genetically male patient with complete androgen insensitivity is externally phenotypically female. Lack of response to adrenal androgens prevents hair formation during puberty (adrenarche).*
29. D – You need to memorize the list of drugs that induce and inhibit CYP450. Warfarin has oodles and oodles of drug reactions for this reason with potentially dire consequences.
30. C – Leydig cells make testosterone. Leydig cell tumors aren’t always physiological active, but those that are can cause masculinization. Granulosa cell tumors, on the other hand, sometimes produce estrogen. Teratomas are oddballs that typically have fat, hair, teeth, etc. Thecomas will not be on your test. Ovarian carcinoid is highly unlikely to show up on your test, but if it did, it would likely present with a classic carcinoid syndrome.*
31. B – This patient has cystic fibrosis. The combination of respiratory and GI issues is classic and caused by ineffective chloride transport and consequently thick exocrine secretions, which clog up the airways and the pancreatic ducts.
32. E – Polycythemia Vera is the red blood cell cancer. Symptoms are related to hyperviscosity of the increased hematocrit. A classic symptom of polycythemia vera is pruritus, typically with exposure to hot water (e.g. the shower). Super high hematocrits are indicative. Low EPO means that the body is responding appropriate by trying to tone down RBC production (which continues autonomously in PCV). JAK2 mutation, test favorite. The classic treatment is bloodletting, like they used to do for everything back in the middle ages.*
33. D – Sensitivity rules things out. It’s TP / (TP + FN). So in order to calculate the sensitivity of this test, we need the true positives (the 90 with cancer) and the false negatives: the patients for whom the test is negative but actually do have prostate cancer. That’s D.*
34. C – Polyarteritis nodosa is that only one that makes sense in explaining the diffuse constellation of symptoms in this question. It affects small and medium arteries, including those involving the skin, heart, kidneys, GI tract, etc. On imaging, a “rosary sign” of small aneurysms strung like beads on a rosary is sometimes mentioned. The biopsy shows an inflamed artery (arteritis). Angiodysplasia typically causes painless GI bleeding (like that seen in diverticulosis). Kawasaki disease is in children (5 days of fever, strawberry tongue, etc). Takayasu arteritis involves big arteries, like the aorta, carotids, and subclavians (with classically diminished upper extremities pulses, hence “pulseless disease”). Thromboangiitis obliterans is also known as Buerger’s disease, a vasculitis seen essentially exclusively in smokers that causes severe peripheral arterial disease (legs much more so than hands). Wegener’s is typified by the combination of renal and lung (and sinus) findings in conjunction. The picture would should granulomas, and C-ANCA would likely be positive, because it’s a board exam.*
35. E – Androgens stimulate sebaceous glands and cause acne. In girls, this is primarily due to adrenarche (DHEA/DHEAS androgen production made by the adrenal gland the zona reticularis). Boys can also blame testosterone from gonadal puberty (pubarche).*
36. B – Six-year-olds typically understand the finality of death. Infants have no understanding, whereas preschool age children often think of deaths in reversible or metaphorical terms.
37. B – Thiazides (typically used as antihypertensives) also increase calcium resorption in the distal tubule and are therefore useful in preventing calcium oxalate stone formation in patients with hypercalciuria (the mechanism is not really worth learning). Thiazides block the Na-Cl symporter, as opposed to loop diuretics, which block the triporter, and acetazolamide, which blocks carbonic anhydrase in the proximal tubule.*
38. A – Pyknosis and nuclear fragmentation are part of the process of apoptosis.
39. A – Acetaminophen (Tylenol) can cause fulminant hepatic failure in overdose. This will probably be on your test.
40. A – The infraspinatus and teres minor are responsible for external rotation. Both the infraspinatus and supraspinatus muscles are innervated by a suprascapular nerve.*
41. B – Osteogenesis imperfecta (blue sclera, lots of fractures [they even occur prenatally]) is a defect in type 1 collagen.
42. C – Filgrastim is a granulocyte colony stimulating factor, which are drugs use to increase white blood cell count in patients with leukopenia. Leucovorin (folinic acid) sounds like it would also be right; it’s used to prevent bone marrow suppression in patients taking methotrexate. Darbepoetin (like erythropoietin) is used to stimulate red blood cell production.*
43. F – A Nystatin mouthwash is the treatment of choice for oral candidiasis. It’s topical, it’s easy, it works. For tongue thrush, the patient can spit it out (and therefore no chance for side effects). For pharyngeal/esophageal candidiasis, the patient can “swish and swallow.” Inhaled cortisteroids, particularly if used without an air chamber (spacer) can cause local immune suppression when contacting the oral mucosa, leading to thrush.*
44. A – Turner syndrome (you may remember lymphedema of the neck by another name: cystic hygroma). The 45,X gives it away though anyway. Mosaic Turner’s syndrome and the mosaic trisomies result from nondisjunction during mitosis. In total monosomy/trisomies, the cause is nondisjunction during meiosis. Uniparental disomy is essentially only tested via the Prader-Willi and Angelman syndromes (chromosome 15).
45. C – GVHD sucks. Skin and GI lesions are especially common sites (mucosal tissues are rapidly dividing and thus prone to attack).
46. D – The baroreceptors are stretch receptors (the more fluid in the vessel, the more they fire). So a patient with hemorrhagic shock will see a decrease in the baroreceptor firing rate. Activation of RAAS will result in increased vascular resistance (vasoconstriction) in order to maintain blood pressure. And capillaries, such as those in the kidney, will be primed for resorption and not filtration (no one wants to pee out good dilute urine when they’re dehydrated). Likewise, systemic capillaries will prefer to hold onto plasma and not let it leak into the interstitium (third-spacing).*

Block 2

47. C – Home canned/bottled food is a buzz-term for botulism. That’s also why the bottles you buy in the store have that little pop up lid that stick out when you open it. If there’s botulism forming air in the bottle, then the lid pops up (and you shouldn’t eat it!). Botulinum toxin inhibits the release of acetylcholine (which actives the nicotinic receptors necessary for skeletal muscle contraction).*
48. C – Blood flow also increases during exercise. The more anaerobic metabolism you use and lactate build-up you have, the more hyperemia you need to clear out the waste products.
49. B – Aminoglycoside antibiotics (gentamycin, amikacin, etc) are powerful antibiotics especially useful for bad gram negative infections. Bad side effects are permanent hearing loss (ototoxicity) and renal failure. Both are important to know. Torsades de Pointes (choice E) can be caused by fluoroquinolones (e.g. cipro), as these drugs prolong the QT-interval.
50. B – Memorize aspirin’s acid-base effects: metabolic acidosis and respiratory alkalosis. Note, this is actual respiratory alkalosis, not simply normal respiratory compensation for metabolic acidosis.
51. C – This patient has hepatitis (elevated liver enzymes) due to active Hepatitis C infection. Hep C and HIV infection are both associated with intravenous drug use. While most patients with Hep A will clear the virus after their acute illness, Hep C causes chronic infection in 80% of patients, which may lead to cirrhosis over time (~20 years).*
52. C – Osgood-Schlatter is also known as apophysitis of the tibial tubercle. It’s due to chronic stress/irritation at the insertion of the patellar ligament on the tibial tubercle. It’s classically seen in teenagers doing repetitive vigorous activity (running, jumping). The radiograph demonstrates classic fragmentation of the tibial tubercle (which isn’t necessary to know to get the question correct).*
53. E – Gram positive rods in a diabetic foot wound (or a World War I soldier fighting in a trench) means Clostridium perfringens (the causative organism of gas gangrene). Crepitus means gas in the tissues, which is produced as a byproduct of its highly virulent alpha toxin.*
54. D – Those are varicose veins, and they’ve described symptomatic varicosities. Incompetent valves allow reflux of blood into the dependent feet and legs. The pooling blood increases hydrostatic pressure, causing edema.
55. A – Electrical alternans on boards means a big pericardial effusion (and usually cardiac tamponade). The heart cannot fill properly, preload decreases, hypotension and tachycardia ensue, fluid backup leads to elevated JVP.*
56. D – Antibiotic-associated diarrhea caused by clostridium difficile can be tenacious, difficult to treat, and even fatal. Alcohol-based rubs are not sufficient to kill the spores. Handwashing with soap is necessary, and equipment should be autoclaved to clean it.
57. A – Ballet dancers (wrestlers, models, ballet dancers, athletes who need to make weight, and particularly young women in general) all have eating disorders on Step 1. Folic acid is involved in the production of both red and white blood cells. Remember, low folate leads to macrocytic anemia and hypersegmented neutrophils. B12 deficiency (not an answer choice) leads to macrocytic anemia and neurological changes (including SCID in severe cases).
58. D – ITP causes immune-mediated consumption of platelets, hence the low platelet count and petechiae. The bone marrow biopsy results demonstrate that the body has appropriately increased platelet production, meaning that this is not a platelet production issue. While TTP has a similar acronym, it’s an entirely different disease with a classic pentad: thrombocytopenia (low platelet count), microangiopathic hemolytic anemia, altered mental status, renal failure, and fever.
59. G – Vincristine (a mitosis inhibitor) frequently causes peripheral neuropathy, which can be severe and irreversible. Other fun associations are Bleomycin with pulmonary fibrosis, Cyclophosphamide and bladder cancer, and Doxorubicin with dilated cardiomyopathy.*
60. D – The arrowed fluid is contained in a space behind the stomach but in front of the retroperitoneal structures (e.g. the pancreas), i.e. the lesser sac.*
61. D – People in their 60s don’t spontaneously become schizophrenic with any frequency for that to be ever be the correct answer. Likewise, Alzheimer’s is a slowly progressive cognitive decline (dementia), not an acute decline in mental status (i.e. delirium). This patient is delirious. Common causes in the elderly includes medications, infections, and being in the hospital (particularly the ICU).*
62. C – Anaphylaxis is treated with epinephrine.
63. C – Logic would dictate that a fracture of the inferior orbital wall might affect the infraorbital artery, and logic would be right.*
64. C -This is obviously a clinical trial. If you know you are getting a drug, then you are not blinded: it’s an open label trial. There is no randomization as there is only a single treatment group.*
65. C – Ah, you really want to pick A for cat scratch fever. But sore throat, adenopathy, and a positive Heterophile antibody test means mononucleosis (i.e. Mono), caused by Epstein-Barr Virus. The heterophile antibody test is due to a cross reaction with horse or sheep red blood cells, which are agglutinated in vitro by the antibodies in the patient’s serum.*
66. C – RSV, like all respiratory viruses, spreads via respiratory droplet. Babies are too young to wheeze because of asthma; they wheeze because of RSV.
67. A – Malonyl-CoA inhibits the rate-limiting step in the beta oxidation of fatty acid. Logically, resting muscle requires less energy (and thus less need for fatty acid breakdown) than active muscle.*
68. D – Recurrent respiratory infections could be a lot of things. But then they mention the dextrocardia. Kartagener syndrome is the combination of situs inversus and defective cilia (due to a mutation in dynein), where the inability to effectively clear secretions results in recurrent sinusitis and bronchiectasis.
69. B – Choriocarcinoma is a much-feared complication of a molar pregnancy. It is a cancer of the bHCG-producing syncytiotrophoblasts found in the placenta.
70. D – The suprachiasmatic nucleus of the hypothalamus controls circadian rhythms. A few more key thalamic nuclei are worth knowing: Supraoptic releases vasopressin (ADH). The lateral nucleus controls thirst and hunger. The ventromedial controls satiety. Anterior controls temperature. The paraventricular nucleus releases CRH, TRH, and oxytocin.
71. B – This patient has symptomatic anemia. Its microcytic nature implies iron deficiency, which is most commonly due to occult blood loss. In the elderly, the concern is colon cancer. In a reproductive age female, iron deficiency is more commonly secondary to uterine pathology.
72. C – Factor V leiden is by far the most common heritable cause of hypercoagulability. Keep in mind that many “most likely” questions are actually asking you for the “most common” cause.*
73. D –  This is rheumatic fever from group A strep pharyngitis. This is thankfully rare now, as we routinely treat Step throat with antibiotics. The cause of all the damage is due to cross-reactivity of Strep antigens with the tissues of the heart, joints, skin, and brain. Anti-streptolysin O (ASO) and anti-DNase titers will be high.
74. D – The Odds Ratio (OR), if you don’t simply have it memorized, is computed exactly as you would guess. It’s the odds of you getting a disease with the treatment (or risk factor) over the odds of you getting a disease without the treatment. In this case: 100/200 divided by 300/300 = 1/2.*
75. D – Rickets. “Pectus carinatum” is also known as “pigeon chest” (protruding sternum) and “bead-like enlargement of the costochondral junctions” is describing a rachitic rosary. Rickets is caused by vitamin D deficiency (either dietary or functional). Osteoblasts in patients with rickets lay down excess unmineralized osteoid, as they are less able to mineralize osteoid into mature bone without sufficient vitamin D.*
76. C – Lymphatic spread of disease moves through lymphatic channels from distal to proximal. The medial side drains to the superficial inguinal nodes. Much of the lateral side will stop at the popliteal nodes prior to ascending the thigh.
77. G – Sulfonylurea medications (glipizide, glyburide) stimulate the pancreas to secrete more insulin. For this reason, they are most efficacious early in the disease process when pancreas still has remaining functional reserve.
78. E – Those are sickle cells on the smear. LUQ pain on test questions almost always means splenic pathology. All sickle cell kids will eventually infarct their spleen.
79. E – Subacute combined degeneration (progressive peripheral sensory and motor loss) is a late sign of B12 deficiency, which is common in old people. On board exams, a geriatric patient who lives alone and may have a “tea and toast” diet is likely to have vitamin deficiencies, particularly of folate and B12.
80. D – An OR greater than 1 signifies increases odds/risk/likelihood. If the 95% CI range does not include 1, then the difference is statistically significant (though not necessarily clinically meaningful).*
81. C – Common sense is key, particularly for counseling-type questions. Patients have autonomy and can do whatever they want; it’s your job to explain the risks and benefits. The patients ultimately make their own treatment choices.
82. D – She is taking anabolic (androgenic) steroids as a performance enhancing drug. Being an athlete on Step 1 is never a good thing.*
83. A – A new blistering disease in an older person is typically going to be a pemphigus question. Then you just have to remember the difference between bullous pemphigoid vs pemphigus vulgaris. Bullous pemphigoid is characterized be the loss of hemidesmosomes that bind keratinocytes to the basement membrane, resulting in bulla (big blisters) in areas of friction, choice A. Patients with pemphigus vulgaris lose their desmosomes (which bind keratinocytes to each other), so that their skin is super friable, which results in ulceration. Mouth ulcers are more common in PV.*
84. B – This is a (prospective) case series. There is no control (and certainly no blinding).*
85. D – Pregnant patients should avoid fish and seafood products that are high in mercury. In general, this means that shellfish and big salt-water fish should be avoided (tuna, swordfish, shark, king mackerel, tilefish, etc)*
86. A – Air and fluid = hydropneumothorax. If that fluid is blood (s/p stabbing), it’s a hemopneumothorax. Lack of mediastinal shift indicates that it’s not under tension.*
87. C – Middle-aged woman with progressive shortness of breath? Think of idiopathic pulmonary fibrosis, a restrictive lung disease.
88. B – Finasteride (aka Propecia) is used for male pattern baldness and prostate hypertrophy. It’s a 5-alpha-reductase inhibitor, which prevents the conversion of testosterone to dihydrotestosterone (DHT).
89. B – Gout, gout, gout. Allopurinol helps prevent flares but does nothing to treat them. Treatments of choice for an acute flare are NSAIDS or colchicine.
90. E – Splitting is an immature defense mechanism often employed by patients with borderline personality disorder. When splitting, a person fails to see others as capable of having both positive and negative qualities; at any given time, it’s all or nothing.*
91. F – Prolonged bleeding time with normal clotting factors (as evidenced by normal PT/INR and PTT) and a sufficient platelet count is going to be von Willebrand disease, the most common hereditary coagulation abnormality, which by either deficiency or mutation results in dysfunctional platelets. A temporary treatment for uncontrolled bleeding is vasopressin, which causes for addition vWf release. Factor VIII concentrate is a more dramatic and more effective treatment, as it also contains vWf.*
92. D – Diffuse low-level ST elevation means pericarditis. These patients often complain of pleuritic chest pain, which is somewhat alleviated by sitting up and leaning forward, and have distant heart sounds. Common test causes include viruses, uremia, and 2-3 weeks after myocardial infarction (Dressler syndrome). *

Block 3

93. E – Profuse super-watery diarrhea means cholera (the so-called “rice water stool”). That said, regardless of the cause, you treat all causes of volume loss with volume replacement (normal saline)!
94. D – Torticollis is a type of focal dystonia, which is a type of EPS (extrapyramidal symptoms) caused by neuroleptics (antipsychotics), such as haloperidol. Uncontrollable facial grimacing is a description of tardive dyskinesia, a rarer sometimes permanent EPS more associated with long-term antipsychotic use.*
95. C – That’s a litany of symptoms with only one reasonable single possible cause out of the provided choices: hyperthyroidism. Elevated thyroid hormone can manifest as anxiety, GI hypermotility, tachycardia and a-fib, weight loss, heat intolerance, etc. Thyroid disorders are very high yield. Pheochromocytomas (choice E) can cause some of the same symptoms in an episodic fashion (more typically panic attacks, episodic severe hypertension, headache).
96. A – Narcotic use for acutely painful conditions is both reasonable and important. Short-term use (immediately post-surgical) does not lead to long term dependence. And yes, drugs addicts should also receive narcotics to control pain.*
97. E – The most important cause of papillary necrosis is analgesia [abuse] nephropathy, a type of kidney damage caused by long-term use of OTC pain medications. Ischemia from disruption of blood flow from the vasa recta causes necrosis and sloughing of the renal papilla. Hematuria and sterile pyuria are common.*
98. A – Altitude sickness can cause high-altitude pulmonary edema (a type of ARDS). The x-ray demonstrates diffuse bilateral fluffy infiltrates.*
99. A – The genetic questions always seem to hinge on remembering (or deducing) that T in DNA is replaced by U in RNA.*
100. B – If you think about this logically, what we have here is a congenital intolerance to breastmilk: galactosemia, in which the body cannot convert galactose to glucose (resulting in an accumulation of Galactose 1-phosphate). They then list the findings and tests used to diagnose it. Lactose (the disaccharide in milk) is composed of glucose + galactose.*
101. E – Endothelial tight junctions’ permeability is increased in response to injury and inflammation, allowing migration of white blood cells and friends to the site of injury.*
102. E – Ventricular fibrillation is the most common cause of sudden cardiac death immediately after myocardial infarction. This is why we have AEDs all over the place now. Papillary muscle rupture classically occurs 2-7 days after an MI and results in massive life-threatening mitral regurgitation. Free ventricular wall rupture after an MI can result in cardiac tamponade. *
103. E – PPIs raise pH by preventing the normal secretion of HCl into the stomach by parietal cells. The body attempts to counteract this unnaturally basic gastric pH with compensatory hypertrophy. If our medications are moving a measured element beyond its set-point, the body nearly always tries to compensate.*
104. E – The whole afferent/efferent thing is worth knowing. When the efferent arteriole is independently constricted, the blood can get into the glomerulus but has difficulty getting out. So more blood spends a greater amount of time in the glomerulus being filtered: GFR up, filtration fraction up, but overall blood flow is decreased due to the increased resistance of the system as a whole.
105. A – Benzodiazepines (including alprazolam aka Xanax) are effective at treating anxiety conditions. Ideally, their use should be limited to bridge therapy awaiting the efficacy of safer less habit-forming maintenance medications like SSRIs and buspirone.*
106. C – If you don’t eat enough calories to run your metabolism, your body will mobilize its stores. We “burn” fat through fatty acid oxidation.
107. E – Chronic microcytic anemia in a patient with normal iron studies should make you think of thalassemia. β-Thalassemia minor is the most common and is typically quite mild. As there is decreased beta chain production, there is a relative excess of alpha chains.*
108. E – Tetracycline use during childhood is commonly associated with tooth discoloration, typically yellow-brown (sometimes described as gray).*
109. A – Targetoid rash after a woodland excursion means lyme disease, caused by Borrelia burgdorferi, carried by the Ixodes tick. Rash (erythema migrans), viral syndrome symptoms, fatigue, and poly-arthritis are common. Lyme carditis typically manifests as AV block.*
110. A – Adalimumab is the only TNF inhibitor on the list. The fancy targeted therapies are all monoclonal antibodies and thus end in ab.*
111. B – The arrow is pointing to a neutrophil (multilobed nucleus). Main fighter of the immune system in acute inflammation and bacterial infection (such as aspiration pneumonia). C5a is a chemotactic factor for PMNs.*
112. C – AIDS retinitis is caused by CMV (typically seen with CD4 count less than 50). Treatment is with ganciclovir.*
113. E – This patient has stress incontinence, a common complaint in women after vaginal childbirth, the risk of which increases with number of deliveries, the size of the baby, and use of forceps, etc. The pelvic floor muscles and urogenital diaphragm are innervated primarily by the S3-4 nerve roots.*
114. A – Chronic anovulation is a common cause of infertility. Long periods are often anovulatory, where lack of an LH surge leads to unchecked estrogen and prevents ovulation and the secretory and menstrual phases that follow, leading to chronic proliferative-phase endometrium and irregular menses, which can be long or short, often light (as only the endometrial tissue that outgrows its blood supply sloughs off).*
115. A – GBS comes from a mother’s colonized vagina and is the most common cause of neonatal sepsis. Women who are GBS+ should receive PCN prophylaxis prior to delivery to prevent exposure to the fetus during delivery.*
116. B – Psychogenic polydipsia (PPD) is associated with several psychiatric conditions, particularly schizophrenia.  It is also sometimes felt to be secondary to the dry/cotton mouth seen with certain medications, including antipsychotics. Patients present with hyponatremia due to their excessive free water intake. In some cases, a water deprivation test is necessary to distinguish PPD from diabetes insipidus.*
117. A – Foot drop after compression in the lower leg = common fibular/peroneal nerve. Nerve compression syndrome = one reason why it’s important that casts not be too tight.*
118. A – The closer R is to 1, the more closely the data points should fit to a line. I think the NBME is trying to imply that I will have poorly controlled diabetes in the future.*
119. E – VEGF is a major tissue growth factor activated by injury, cytokine release (infection, inflammation) and hypoxia that promotes angiogenesis and also increases vascular permeability (hence the edema). This increased permeability aids in the movement of proteins and white blood cells to the site of injury.*
120. C – In this question, they have described the components of congenital rubella. The distributed purpura (a result of extramedullary hematopoiesis) is a description of the classic “blueberry muffin rash” (which you are highly unlikely to hear actually described as such on a test).*
121. B – Fatigable weakness, particularly of the eyes, is classic myasthenia gravis, an autoimmune condition cause by antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction. The arrow is pointing to the patient’s prominent thymus. Thymoma and thymic hyperplasia are both in common in the patients with MG, and thymectomy is curative in a portion of patients. Small cell carcinoma of the lung is associated with Lambert-Eaton myasthenic syndrome, a disease caused by autoantibodies against presynaptic calcium channels. These patients classically begin weak and an experience a “warm up” effect after some use (they ultimately become weak again though).*
122. A – Renal artery stenosis causes decreased blood flow to the supplied kidney, which results in the activation of the Renin-Angiotensin-Aldosterone System, because the hypoperfused kidney secretes renin from the juxtaglomerular cells. The normal kidney has normal renin secretion. However, the additional circulating aldosterone will cause the normal kidney to retain sodium/water.*
123. E – Tons of exercise followed by renal failure is always going to be rhabdomyolysis. Dark urine (without actual blood in it) is due to myoglobinuria, which can cause a false positive urine dipstick.
124. A – In additional to thyroid problems, amiodarone can cause interstitial lung disease, including potentially fatal non-reversible pulmonary fibrosis. Digoxin is famous for its narrow therapeutic range and numerous side effects, including green-yellow vision changes. Lisinopril can cause angioedema, as well as hyperkalemia. Metoprolol can exacerbate asthma in addition to causing dizziness, bradycardia, and hypotension. Procainamide can cause drug-induced lupus.*
125. E – Delayed separation of the umbilical stump is a classic clue for leukocyte adhesion deficiency. ICAM is the defective ligand most often asked about as a second order question.
126. A – This patient has Conn’s syndrome (primary hyperaldosteronism), most commonly caused by a hyperfunctioning adrenal adenoma. This is an important and highly tested cause of refractory hypertension. The patient has lab abnormalities consistent with high aldosterone (high sodium, low potassium, metabolic alkalosis) with an appropriately suppressed renin.*
127. E – A chronic “heaped up” ulcerative lesion of the skin, especially on sun-exposed areas in people who spend time outdoors, means cancer. If it’s keratinocytes at play (and not melanocytes), that leaves you with either squamous cell or basal cell carcinoma.
128. B – Alcoholics (and any person with an altered level of consciousness) are a set-up for aspiration pneumonia: classically RLL, classically foul-smelling. The organism on tests will be Klebsiella.
129. D – Cholesterol xanthomas, horrible serum cholesterol levels, and early death by MI are all signs of familial hypercholesterolemia (caused by a defect in the LDL receptor).
130. E – All of the congenital heart defects and their associated murmurs are high-yield and worth memorizing. Understanding murmur physiology is also high yield in general. In this case, we have a cyanotic heart condition in a newborn. Tetralogy of Fallot is the most common cyanotic heart lesion on tests and in real life. ASDs–fixed split S2–are left-to-right (non-cyanotic lesions), at least until they reverse down the line (Eisenmenger syndrome). Clinically significant PDAs are alluded to by their continuous “machinery” murmur.
131. E – This is what a correlation is. A negative r-value means that the relationship between the variables is inverse (not direct), so as one goes up, the other goes down.*
132. A – An annular pancreas occurs when the pancreas is wrapped around the second (descending) portion of the duodenum. When symptomatic (in adults, typically when there is superimposed pancreatitis), it can block flow of GI contents through the intestines.*
133. B – The left sided system is much higher pressure than the right side, hence the aortic valve closing is usually louder than pulmonic valve. A P2 louder than A2 means that the pulmonary artery pressure is significantly elevated.*
134. E – Calcium oxalate stones are the most common variety of kidney stones, but uric acid stones make up 5-10% as well. None of the other choices are associated with renal calculi of any variety.*
135. E – The patient’s chronic inflammatory pneumonitis is killing off his lung parenchyma (composed primarily of type I pneumocytes). Type II pneumocytes, in addition to making surfactant, can replicate in order to replace type I pneumocytes, so they will be increased. Chronic interstitial inflammation results in fibrosis, hence an increase in fibroblasts.*
136. H – Furosemide is the prototypical “loop” diuretic, which works by blocking the triporter and preventing the reabsorption of 1 K, 1 Na, and 2 Cl ions. So less K/Na/Cl ion transport causes decreased osmolarity of the medullary interstitium (where these ions would normally enter). Water follows solute, so with less ions reabsorbed, less water will be reabsorbed.
137. B – Surgical portosystemic shunts are most often performed by anastomosing the splenic vein to the nearby left renal vein. The splenic and SMV join to form the main portal vein. are portal system veins. More commonly, a TIPS procedure is performed to create an intrahepatic shunt between the portal and hepatic veins.*
138. C – If an adult is taking on behaviors common to children, it’s called regression (don’t feel bad if it’s something you might do yourself).

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

You may also enjoy some other entries in the USMLE Step 1 series:
— How to approach the USMLE Step 1
— How to approach NBME/USMLE questions
— Free USMLE Step 1 Questions
— Last year’s USMLE “Free 150” explanations (2013-14)