Simultaneous Diffuse Alveolar Hemorrhage and Acute Myocarditis in an Immunocompetent Adult with a Human Metapneumovirus Infection: A Case Report

Human metapneumovirus (hMPV), which can cause severe lower respiratory tract disease and, rarely, extrapulmonary complications, was identified in a 64-year-old immunocompetent man who presented with acute hypoxemia, bronchoscopic evidence of diffuse alveolar hemorrhage (DAH), and clinically diagnosed acute myocarditis. Notably, hMPV was detected by multiplex PCR on a bronchoalveolar lavage (BAL) sample despite an initial negative upper airway evaluation. The patient's condition was severe and required invasive mechanical ventilation and inotropic support. After the viral etiology was identified, empiric steroids were discontinued, the patient recovered, and his left ventricular ejection fraction improved from ~9% to 40% at discharge. This case underscores the fact that during the hMPV season, acute hypoxemia with diffuse opacities should prompt consideration of infectious DAH and that lower-respiratory multiplex PCR (from BAL or deep tracheal aspirate) can identify pathogens when upper airway tests are negative. It also highlights that, in unexplained DAH, empirical immunosuppression should be used cautiously to perform a full infectious evaluation. Furthermore, when myocarditis is suspected, timely hemodynamic assessment and consideration of mechanical circulatory support may influence the outcomes.