Fungal myocarditis and pericardial effusion secondary to Inonotus tropicalis (phylum Basidiomycota) in a dog

Fungal disease is a rare cause of pericardial effusion in dogs. This report describes the first case of fungal pericardial effusion and myocarditis secondary to the fungal organism Inonotus tropicalis. A 9-year-old female spayed French bulldog with a multi-year history of treatment with glucocorticoids for management of atopy was presented for exercise intolerance, ascites and weight loss. Physical examination and thoracic imaging revealed enlarged peripheral and cranial mediastinal lymph nodes, left ventricular thickening and cardiac tamponade secondary to pericardial effusion. Fine needle aspiration of the cranial mediastinal lymph node showed pyogranulomatous inflammation with short, thin and poorly septated hyphae. Culture of the aspirate yielded a fungal isolate identified as Inonotus tropicalis based on morphologic features and rRNA gene sequencing. Postmortem examination showed myocardial thickening with multifocal to coalescing, firm, white, ill-defined nodules. Histology confirmed the presence of disseminated fungal infection with extensive myocardial involvement. Inonotus tropicalis is an opportunistic poroid wood-decaying basidiomycete. Infection in this dog was likely the result of chronic immunosuppressive therapy.