Trap Pattern Library

Brachial Plexus Injury — Don't Confuse Trunks and Cords

When the stem mentions an upper trunk (Erb-Duchenne) injury, the answer is NOT about specific nerve branches like axillary or radial. Upper trunk = C5-C6 = muscles supplied by those roots.

Claw Hand — Ulnar vs Median vs Both

Claw hand is NOT always ulnar nerve. Look for which fingers are clawed. Ulnar claw = ring & little finger. Median claw = index & middle finger. Combined claw = all fingers (median + ulnar).

Aspiration Pneumonia — NOT Always the Right Lung

Aspiration pneumonia in a SUPINE patient affects the posterior segment of the RIGHT upper lobe or superior segment of the RIGHT lower lobe. But in a STANDING patient, it's the RIGHT lower lobe. The trap: they ask about a specific position.

Myocardial Infarction with Normal Coronaries

Not all MI is from atherosclerosis. If a young woman presents with chest pain + ST changes, DON'T immediately pick 'atherosclerotic CAD'. Consider MINOCA, vasospasm, spontaneous coronary artery dissection (SCAD), or takotsubo.

Diabetic Ketoacidosis — Potassium Paradox

In DKA, initial serum K+ is often ELEVATED (despite total body K+ depletion). The trap: they ask about potassium on admission, and students pick 'hypokalemia' because insulin deficiency causes K+ loss.

Acute Abdomen — Peritonitis vs Obstruction

Board-like rigidity with absent bowel sounds = PERITONITIS (surgical emergency). Distension with high-pitched tinkling sounds = OBSTRUCTION. The trap: stem describes a patient with severe abdominal pain and distension, students pick obstruction when it's peritonitis or vice versa.

Meningitis — CSF Picture Traps

NEVER diagnose based on ONE CSF parameter alone. Low glucose + high protein + neutrophils = BACTERIAL. Low/normal glucose + high protein + lymphocytes = TUBERCULOUS. Normal glucose + normal protein + lymphocytes = VIRAL. The trap: they give a mixed picture.

Jaundice — Direct vs Indirect Trap

Hemolytic jaundice = INDIRECT (unconjugated). Obstructive jaundice = DIRECT (conjugated). The trap: they ask about 'increased urobilinogen' — students think obstruction because they associate it with bile, but urobilinogen is INCREASED in hemolysis and DECREASED in obstruction.

Thyroid Eye Disease — Don't Confuse With Myasthenia

Diplopia + Ptosis can be EITHER thyroid eye disease (TED) OR myasthenia gravis (MG). The trap: stem describes a patient with diplopia and ptosis, students jump to myasthenia because of the classic eye findings. But TED has lid lag, proptosis, and restriction on upgaze.

Parkinson's — Rest Tremor vs Essential Tremor

Rest tremor = PARKINSON'S. Action tremor (intention) = CEREBELLAR. Postural tremor (sustained position) = ESSENTIAL TREMOR. The trap: they describe a patient with tremor and bradykinesia, students pick 'essential tremor' because they're more familiar with it.

Nephrotic vs Nephritic — The Proteinuria Trap

NEPHROTIC = massive proteinuria (>3.5g/day) + edema + hypoalbuminemia. NEPHRITIC = hematuria + hypertension + oliguria + mild proteinuria. The trap: They give a patient with hematuria AND massive proteinuria — students get confused.

Scaphoid Fracture — X-ray NOT Always Positive Initially

Scaphoid fracture may be X-ray NEGATIVE in the first 2 weeks. The trap: the stem says 'normal X-ray' and students pick 'no fracture'. But if there's snuffbox tenderness after a FOOSH injury, treat as scaphoid fracture regardless.

Pneumothorax — Needle Decompression Site Trick

Needle decompression for tension pneumothorax = 2nd intercostal space, MIDCLAVICULAR line. Chest tube insertion = 5th intercostal space, MIDAXILLARY line. The trap: they mix up the lines.

TB Treatment — Rifampicin Interactions

Rifampicin is a POTENT CYP450 INDUCER. It reduces levels of OCPs, warfarin, sulfonylureas, and many other drugs. The trap: they ask about a patient on ATT who becomes pregnant or has uncontrolled blood sugar — students think the drug is not working, not that it's an interaction.

Acute Pancreatitis — Lipase vs Amylase

LIPASE is MORE specific and stays elevated LONGER than amylase for pancreatitis. But many questions still use amylase. The trap: they ask about a patient with abdominal pain and an elevated amylase, but amylase can be elevated in many non-pancreatic conditions.

Post-Streptococcal Glomerulonephritis — Timing Trap

PSGN occurs 1-3 weeks AFTER Strep infection (usually pharyngitis or impetigo). Acute rheumatic fever occurs 2-3 weeks AFTER. The trap: stem gives a patient with recent sore throat who now has hematuria — students pick ARF instead of PSGN.

Cranial Nerve III Palsy — 'Down and Out' Trap

CN III palsy = eye is 'down and out' (due to unopposed action of LR (CN VI) and SO (CN IV)). The trap: students remember 'down and out' but forget that ptosis is ALSO present (due to loss of levator palpebrae superioris). If there's NO ptosis, it's NOT a complete CN III palsy.

Diabetic Foot — X-Ray Doesn't Rule Out Osteomyelitis

X-ray changes in osteomyelitis take 10-14 days to appear. The trap: stem says 'normal X-ray' and students pick 'cellulitis, not osteomyelitis'. But if a probe-to-bone test is positive or there's an ulcer over a bony prominence, treat as osteomyelitis even with normal X-ray.

Hypokalemia — ECG Changes Order

Hypokalemia ECG changes progress in order: (1) U waves, (2) T wave flattening, (3) ST depression, (4) QRS widening. The trap: students pick 'peaked T waves' (which is HYPERKALEMIA) because they confuse the two.

Liver Function — Transaminitis Pattern Recognition

AST > ALT = alcoholic liver disease (AST:ALT usually 2:1). ALT > AST = viral hepatitis. Both are elevated but the RATIO tells you the etiology. The trap: they give raw numbers without ratio interpretation.