Pericarditis vs. endocarditis

Pericarditis and endocarditis are both cardiac inflammatory conditions, but they affect opposite layers of the heart. Pericarditis involves the pericardium, the fibrous sac enclosing the heart. Endocarditis involves the endocardium, the heart's inner lining — and in practice almost always means infection of the heart valves. (Inflammation of the muscular middle layer is myocarditis.)

Pericarditis typically presents with sharp, pleuritic chest pain that worsens when lying flat and improves when sitting up and leaning forward. Classic findings include a pericardial friction rub on auscultation and diffuse ST-segment elevation on ECG. Common causes are viral infection, recent myocardial infarction, uremia, autoimmune disease, and malignancy. Complications include pericardial effusion and, if fluid accumulates under pressure, cardiac tamponade.

Infective endocarditis presents very differently: fever, a new or changing heart murmur, and signs of systemic embolization. Vegetations — clumps of organisms and thrombus on valve leaflets — can shower emboli, producing findings like splinter hemorrhages, Janeway lesions, and Osler nodes. Risk factors include abnormal or prosthetic valves, intravenous drug use, and bacteremia; typical organisms are Staphylococcus aureus and viridans streptococci. Diagnosis rests on blood cultures and echocardiography, organized by the Duke criteria.

USMLE Step 1 tests these conditions side by side with myocarditis, and vignettes hinge on the distinguishing features: positional chest pain with a friction rub points to pericarditis, while fever plus a new murmur in a patient with valve disease or IV drug use points to endocarditis.