NBME CBSE cheat sheet

Major depressive disorder requires at least 5 of 9 symptoms lasting 2 weeks or more, including depressed mood or anhedonia.

Alcohol withdrawal is treated with benzodiazepines, with dosing guided by a withdrawal scale such as the CIWA-Ar.

Wernicke encephalopathy (confusion, ataxia, ophthalmoplegia) requires thiamine before any glucose administration.

Naloxone reverses opioid overdose; flumazenil reverses benzodiazepines but can precipitate seizures in dependent patients.

Disulfiram inhibits aldehyde dehydrogenase, causing acetaldehyde accumulation and flushing, nausea and tachycardia with alcohol.

Serotonin syndrome: clonus, hyperreflexia, hyperthermia and agitation from serotonergic combinations such as an SSRI plus an MAOI.

Neuroleptic malignant syndrome: lead-pipe rigidity, hyperthermia and elevated creatine kinase; treated with dantrolene or bromocriptine.

Buprenorphine and methadone, both mu-opioid agonists, are first-line pharmacotherapy for opioid use disorder.

Sensitivity = TP/(TP+FN) and specificity = TN/(TN+FP); both are intrinsic properties of a test and do not change with prevalence.

PPV = TP/(TP+FP) rises as disease prevalence rises, while NPV falls as prevalence rises.

Relative risk = incidence in exposed divided by incidence in unexposed, and is calculated in cohort studies.

Odds ratio = (a x d)/(b x c), calculated in case-control studies; it approximates relative risk when the disease is rare.

Number needed to treat = 1 divided by the absolute risk reduction.

Type I error is alpha (false positive); type II error is beta, and statistical power equals 1 minus beta.

At steady state, prevalence is approximately incidence multiplied by average disease duration.

Herd immunity threshold = 1 minus 1/R0, where R0 is the basic reproduction number.

A 95% confidence interval that excludes the null value corresponds to P less than 0.05.

Iron deficiency anemia: microcytic anemia with low ferritin, high TIBC and low transferrin saturation.

Anemia of chronic disease: low serum iron, low TIBC, high ferritin and elevated ESR or CRP.

Thalassemia trait: microcytosis out of proportion to the degree of anemia, with normal ferritin and elevated HbA2.

Vitamin B12 deficiency: macrocytic anemia, hypersegmented neutrophils, neurologic deficits and elevated methylmalonic acid.

Folate deficiency: macrocytic anemia without neurologic findings and with a normal methylmalonic acid level.

Sickle cell disease results from glutamic acid to valine substitution at position 6 of beta-globin; parvovirus B19 precipitates an aplastic crisis.

G6PD deficiency produces Heinz bodies and bite cells after oxidative stress such as fava beans, sulfa drugs or primaquine.

TTP: ADAMTS13 deficiency with schistocytes, thrombocytopenia, renal failure and neurologic signs; treat with plasma exchange.

Hemophilia A: factor VIII deficiency with prolonged PTT and normal PT and bleeding time.

MAP = cardiac output x total peripheral resistance; MAP also approximately equals diastolic pressure plus one third of the pulse pressure.

Frank-Starling relationship: increasing preload increases stroke volume up to a physiologic limit.

Aortic stenosis: crescendo-decrescendo systolic murmur at the right upper sternal border radiating to the carotids, with pulsus parvus et tardus.

Mitral stenosis: opening snap followed by a diastolic rumble, most often after rheumatic fever.

Mitral regurgitation: holosystolic murmur at the apex radiating to the axilla.

Aortic regurgitation: early diastolic decrescendo murmur at the left sternal border with widened pulse pressure.

Ventricular septal defect produces a holosystolic murmur at the left lower sternal border; a patent ductus arteriosus produces a continuous machine-like murmur.

Tetralogy of Fallot: right ventricular outflow obstruction, VSD, overriding aorta and right ventricular hypertrophy; squatting raises systemic vascular resistance and reduces the shunt.

Troponin rises 3 to 6 hours after myocardial infarction, peaks near 24 hours and remains elevated for 7 to 10 days.

Primary hypothyroidism: elevated TSH with low free T4; central hypothyroidism shows low or inappropriately normal TSH.

Hashimoto thyroiditis: anti-thyroid peroxidase antibodies, and the most common cause of hypothyroidism in iodine-sufficient regions.

Graves disease: TSH-receptor stimulating antibodies causing hyperthyroidism, diffuse goiter, exophthalmos and pretibial myxedema.

Diabetes diagnosis: HbA1c of 6.5% or higher, fasting glucose of 126 mg/dL or higher, or 2-hour OGTT glucose of 200 mg/dL or higher.

Diabetic ketoacidosis: anion-gap metabolic acidosis with ketones; total body potassium is depleted even when serum potassium is normal or high.

Primary adrenal insufficiency: low cortisol with high ACTH, hyperpigmentation, hyponatremia and hyperkalemia.

SIADH: euvolemic hypotonic hyponatremia with high urine osmolality and inappropriately high urine sodium.

Primary hyperparathyroidism: elevated calcium, low phosphate and elevated PTH, most often from a single adenoma.

MEN1 syndrome: parathyroid, pituitary and pancreatic neuroendocrine tumors.

Celiac disease: IgA anti-tissue transglutaminase antibodies, villous atrophy with crypt hyperplasia, and HLA-DQ2 or DQ8.

Crohn disease: transmural inflammation, skip lesions, noncaseating granulomas and perianal involvement.

Ulcerative colitis: continuous mucosal inflammation beginning at the rectum, with risk of toxic megacolon and colorectal carcinoma.

Duodenal ulcer pain is relieved by eating, whereas gastric ulcer pain is worsened by eating.

Zollinger-Ellison syndrome: gastrinoma causing multiple refractory ulcers and diarrhea with elevated fasting gastrin.

Acute pancreatitis: elevated lipase and amylase, with gallstones and alcohol as the leading causes.

Wilson disease: low ceruloplasmin, Kayser-Fleischer rings, hemolytic anemia and neuropsychiatric findings.

Hereditary hemochromatosis: elevated ferritin and transferrin saturation with diabetes, arthropathy, hepatomegaly and bronze skin.

Alpha-1 antitrypsin deficiency: early panacinar emphysema plus cirrhosis from retained protein in hepatocytes.

Rate-limiting enzyme of glycolysis is phosphofructokinase-1; of the TCA cycle, it is isocitrate dehydrogenase.

Cyanide inhibits cytochrome c oxidase (complex IV), rotenone inhibits complex I and antimycin A inhibits complex III.

Net ATP yield per glucose is about 30 to 32, varying with the efficiency of the NADH shuttles.

Type I collagen is in bone, skin and tendon; type II in cartilage; type III in blood vessels and early wound; type IV in basement membrane.

Vitamin C is required for hydroxylation of proline and lysine during collagen synthesis and cross-linking.

Hardy-Weinberg equilibrium: p^2 + 2pq + q^2 = 1, and the carrier frequency for a recessive allele is 2pq.

Autosomal dominant traits show male-to-male transmission and no carrier state; X-linked recessive traits show no male-to-male transmission.

Tumor suppressors such as RB, TP53 and APC require loss of both alleles; oncogenes such as RAS and MYC require activation of one allele.

Mitochondrial inheritance is maternal, and heteroplasmy produces variable severity among offspring.

Osteoarthritis: asymmetric joint space narrowing, osteophytes, subchondral sclerosis, and Heberden and Bouchard nodes.

Rheumatoid arthritis: symmetric MCP and PIP involvement, morning stiffness lasting more than 1 hour, and anti-CCP antibodies.

Gout: needle-shaped negatively birefringent monosodium urate crystals; pseudogout: rhomboid positively birefringent calcium pyrophosphate crystals.

Osteoporosis is defined by a DXA T-score of -2.5 or lower.

Paget disease of bone: mosaic trabecular pattern with elevated alkaline phosphatase and normal calcium and phosphate.

Osteomyelitis: Staphylococcus aureus is the most common cause overall, and Salmonella is typical in sickle cell disease.

Pemphigus vulgaris: intraepidermal flaccid bullae with anti-desmoglein antibodies and a positive Nikolsky sign.

Bullous pemphigoid: subepidermal tense bullae with linear IgG along the basement membrane and a negative Nikolsky sign.

Breslow depth of invasion is the single most important prognostic factor in melanoma.

Upper motor neuron lesions cause spasticity, hyperreflexia and a Babinski sign with little atrophy; lower motor neuron lesions cause flaccidity, atrophy, fasciculations and areflexia.

CN III palsy leaves the eye deviated down and out with a dilated pupil.

Peripheral CN VII palsy affects the entire face including the forehead, while a central lesion spares the forehead.

Middle cerebral artery occlusion causes contralateral face and arm weakness, often with aphasia.

Epidural hematoma: torn middle meningeal artery, lens-shaped collection, lucid interval; subdural hematoma: bridging veins, crescent-shaped collection.

Subarachnoid hemorrhage: thunderclap headache with xanthochromia on lumbar puncture.

Parkinson disease: loss of substantia nigra dopaminergic neurons with resting tremor, rigidity and bradykinesia, treated with levodopa-carbidopa.

Multiple sclerosis: periventricular white matter plaques, oligoclonal bands in CSF, and heat-induced worsening known as Uhthoff phenomenon.

Alzheimer disease: amyloid plaques and tau neurofibrillary tangles beginning in the hippocampus.

Creatinine clearance = (urine creatinine x urine volume) divided by plasma creatinine.

The proximal tubule reabsorbs about 65% of filtered sodium along with glucose and amino acids; dysfunction produces Fanconi syndrome.

The thick ascending limb uses the Na-K-2Cl cotransporter, is impermeable to water, and is the site of loop diuretic action.

Thiazides block the distal convoluted tubule Na-Cl cotransporter and can cause hypercalcemia and hyperglycemia.

Prerenal acute kidney injury: BUN/creatinine ratio above 20 and fractional excretion of sodium below 1%.

Acute tubular necrosis: muddy brown casts and fractional excretion of sodium above 2%.

Nephrotic syndrome: proteinuria above 3.5 g/day, hypoalbuminemia, edema and hyperlipidemia; minimal change disease is the most common cause in children.

Post-streptococcal glomerulonephritis: low C3, cola-colored urine and red blood cell casts.

Hyperkalemia ECG progression: peaked T waves, then widened QRS, then a sine wave pattern.

The LH surge triggers ovulation roughly 14 days before the next menses, and progesterone peaks during the luteal phase.

hCG is produced by the syncytiotrophoblast and becomes detectable in serum about 1 week after conception.

Ectopic pregnancy most often implants in the ampulla; risk factors include pelvic inflammatory disease, smoking and prior ectopic pregnancy.

Preeclampsia: new hypertension after 20 weeks with proteinuria or end-organ dysfunction; magnesium sulfate prevents seizures.

Placenta previa causes painless third-trimester bleeding and no digital cervical examination; abruption causes painful bleeding with a tender, tetanic uterus.

Polycystic ovary syndrome (Rotterdam criteria): oligo-ovulation, hyperandrogenism and polycystic ovaries on ultrasound.

Prostate cancer arises in the peripheral zone, while benign prostatic hyperplasia arises in the transitional zone.

Turner syndrome (45,X): streak ovaries, short stature, coarctation of the aorta and cystic hygroma.

Obstructive disease: FEV1/FVC below 0.70 with increased residual volume and total lung capacity.

Restrictive disease: reduced FVC and TLC with a normal or increased FEV1/FVC ratio.

Emphysema: smoking causes centriacinar disease in upper lobes, while alpha-1 antitrypsin deficiency causes panacinar disease in lower lobes.

Asthma: reversible airflow obstruction with Curschmann spirals and Charcot-Leyden crystals.

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia; Klebsiella causes currant-jelly sputum in alcoholics.

Sarcoidosis: bilateral hilar lymphadenopathy and noncaseating granulomas with elevated serum ACE.

ARDS: acute bilateral infiltrates with severe hypoxemia refractory to supplemental oxygen and a low PaO2/FiO2 ratio.

Small cell lung carcinoma is central and paraneoplastic; adenocarcinoma is the most common type and is usually peripheral.