Crucial Role of Pre-antimicrobial Cultures and Histopathological Correlation in the Diagnosis of Culture-Negative Endocarditis: A Case Report.

Infective endocarditis (IE) is a life-threatening infection involving the cardiac valves and endocardium, most commonly associated with streptococci and enterococci in patients with underlying structural cardiac abnormalities. The bicuspid aortic valve (BAV) represents a significant predisposing valvular condition compared with patients with a tricuspid aortic valve. Culture-negative endocarditis accounts for a substantial portion of all cases, often attributed to prior antibiotic exposure, and represents a major diagnostic challenge in which histopathological examination of the surgical specimen becomes the decisive diagnostic tool. We report the case of an elderly male with a known BAV who presented with recurring fever episodes and progressive acute decompensated heart failure. Transthoracic echocardiography demonstrated a highly mobile vegetation on a calcified aortic valve, with severe aortic regurgitation. Empirical antibiotic therapy was initiated prior to surgical referral. Given clinical deterioration, aortic valve replacement was performed. Surgical valve cultures yielded no bacterial growth. Histopathological examination of the resected specimen revealed coagulative necrosis, dystrophic calcification, and Gram-positive structures, confirming the diagnosis of bacterial IE. This case underscores the critical importance of obtaining blood cultures before initiating antibiotic therapy. Furthermore, it highlights the role of histopathological examination when microbiological cultures fail and reinforces the need for a multidisciplinary approach in the management of IE on a BAV.