Purulent Pericarditis Caused by Streptococcus Constellatus Masquerading as St-Elevation Myocardial Infarction: A Diagnostic and Therapeutic Challenge

Background Purulent pericarditis is a rare, life-threatening bacterial infection of the pericardial space, accounting for less than 1% of pericarditis cases with near 100% untreated mortality. A key diagnostic pitfall is its ability to produce diffuse ST segment elevation, mimicking ST elevation myocardial infarction. Streptococcus constellatus is an exceptionally rare causative anaerobe causing deep-seated pyogenic infections. Case Illustration A 49-year-old male was referred for primary percutaneous coronary intervention with a diagnosis of anteroposterior lateral STEMI, presenting with three days of central, stabbing chest pain radiating to the back, productive cough, and one week of fever. Examination revealed a pericardial friction rub and coarse bilateral crackles; electrocardiography showed ST segment elevation in leads II, III, aVF, I, aVL, V5–V6, and V7–V8. Laboratory findings showed leucocytosis, elevated C-reactive protein, and acute kidney injury. Echocardiography demonstrated moderate pericardial effusion, regional wall motion abnormality, reduced right ventricular function, and preserved ejection fraction. Coronary angiography revealed normal coronary arteries, redirecting the diagnosis to pericarditis. The course was complicated by haemodynamic instability, cardiac arrest, hospital-acquired pneumonia, and respiratory failure. Anterolateral thoracotomy yielded 500 mL of purulent fluid; cultures grew Streptococcus constellatus (susceptible to ceftriaxone), tuberculosis was excluded. Treatment included ceftriaxone, colchicine, and supportive care. Conclusion This case underscores that purulent pericarditis may mimic STEMI electrocardiographically, causing critical diagnostic delay. Normal coronary angiography, a pericardial friction rub, and systemic infection are pivotal clues toward the correct diagnosis. Given the fulminant nature and high mortality of this condition, a high index of suspicion, prompt microbiological confirmation, and early source control are imperative.Figure 1.ECG in Emergency Room show diffuse ST Elevation.