A case of an unexplained eosinophilic myocarditis in a dog

An 8-year-old spayed female Munsterlander was evaluated for a chronic low grade fever and a two month history of exercise intolerance. On physical examination, tachycardia and a grade II/VI right systolic heart murmur were detected. Echocardiography revealed marked thickening of the atrial and ventricular walls with mixed echogenicity and concentric hypertrophy of the left and right ventricles and equivocal systolic dysfunction. Serum cardiac troponin I level was markedly elevated. Endomyocardial biopsy was attempted; however, the patient arrested during the procedure and resuscitation was unsuccessful. Post-mortem examination revealed severe, chronic atrial and ventricular eosinophilic myocarditis associated with marked interstitial fibrosis. Serological testing, histopathology and immunohistochemistry staining did not reveal an underlying infectious agent or neoplasm. To our knowledge, this is the first reported case of primary eosinophilic myocarditis in the absence of a peripheral eosinophilia and multi-organ eosinophilic inflammation in a dog.