Internal Medicine: Structured Reasoning at the Bedside
Core concepts
Internal medicine questions reward a disciplined approach: define the syndrome, generate a short differential, then let discriminating features narrow it. Master the cardinal presentations - chest pain, dyspnoea, fever, oedema, jaundice, altered consciousness, polyuria, weight loss - and the physiological basis of each. Know the diagnostic criteria you can recite: features of nephrotic versus nephritic syndrome, the metabolic syndrome, diabetic ketoacidosis versus hyperosmolar state, and the classification of anaemias by mean corpuscular volume. Electrolyte and acid–base interpretation is high-yield: calculate the anion gap, then the delta ratio, and check compensation with Winter's formula. Cardiology rewards pattern recognition - ECG territory mapping, the timing of troponin rise, and the difference between heart failure with reduced and preserved ejection fraction. Endocrinology questions often hinge on a single confirmatory test and its interpretation.
Traps
Questions frequently offer a plausible but wrong test order, or a treatment before confirmation. Watch for 'most likely' versus 'next best step' - the answer changes. Beware distractors that describe a complication rather than the primary diagnosis, and remember that normal-range values can still be abnormal for the patient (for example, a 'normal' potassium in a patient with renal failure and acidosis). Read units carefully; glucose in mmol/L versus mg/dL changes the threshold you apply.
Rule of thumb
For any metabolic derangement, ask three questions in order: what is the primary disorder, is compensation appropriate, and what is the underlying cause? Correct the cause, not just the number.
Worked example
A patient with vomiting has pH 7.50, PaCO₂ 48 mmHg, bicarbonate 36 mmol/L. The primary disorder is metabolic alkalosis; the raised CO₂ is appropriate respiratory compensation, not a primary respiratory acidosis. Look for diuretic use or gastric losses.