Internal Medicine: Core Reasoning and Common Traps
Internal medicine questions reward a disciplined diagnostic sequence: identify the dominant syndrome, generate a ranked differential, and let discriminating features (onset, laterality, associated symptoms, response to prior therapy) narrow it. You must be fluent in the classic presentations of cardiopulmonary disease (acute coronary syndrome, heart failure, COPD/asthma exacerbation, pulmonary embolism), endocrine and metabolic disorders (diabetes, thyroid disease, adrenal insufficiency, electrolyte derangements), and the systemic diseases that present with fever, weight loss, or multi-organ involvement.
Concepts to master
- Hemodynamic reasoning: mean arterial pressure, pulse pressure, jugular venous distension, and how they shift in shock states.
- Acid–base interpretation: calculate the anion gap, then the delta ratio; check compensation before calling a disorder "mixed."
- Electrolytes: corrected sodium in hyperglycemia, ECG changes of potassium disorders, and the dangers of over-rapid correction.
- Antibiotic and anticoagulant selection grounded in the likely organism or clot burden, not habit.
Traps
Questions often hide the diagnosis behind a normal-looking value (e.g., a "normal" anion gap in a hypoalbuminemic patient) or a single atypical feature. Beware answer choices that treat a symptom rather than the cause, and distractors that are correct statements but irrelevant to the stem. Timing cues ("sudden onset," "over weeks") frequently separate vascular from inflammatory causes.
Worked rule of thumb
For any acid–base stem: (1) identify primary disorder from pH and PCO₂/HCO₃⁻, (2) compute expected compensation, (3) compute anion gap; if elevated, compute delta ratio. A delta ratio <1 suggests a concurrent non-gap acidosis; >2 suggests concurrent metabolic alkalosis. This single algorithm answers most mixed-disorder questions.