SPONTANEOUS CARDIOMYOPATHY AND EXOPHTHALMOS IN COTTON RATS (SIGMODON HISPIDUS)

Exophthalmos and clinical signs of heart failure occurred sporadically in 3- to 12-month-old cotton rats (Sigmodon hispidus) in a colony ori ginally derived from three male and four female littermates. Macroscop ic lesions in severely affected animals included subcutaneous edema, h ydrothorax, right ventricular dilatation, unilateral or bilateral atri al thrombosis, and exophthalmos. Hearts from 17 cotton rats that were found dead or were euthanatized because of exophthalmos or dyspnea and 33 control cotton rats were examined microscopically. Myocardial lesi ons were present in 46 of 46 cotton rats greater than or equal to 1 mo nth of age and consisted of multifocal cardiac myocyte necrosis, miner alization, and mononuclear inflammatory cell infiltration. Cotton rats >5 months of age also had foci of interstitial fibrosis and myocyte a trophy. Twelve of 24 (50%) necropsied cotton rats had chronic pulmonar y congestion, and livers from eight of 24 (33%) had chronic periacinar congestion and atrophy. Thrombi were present in one or both cardiac a tria in nine of 50 (18%) hearts, and in at least one orbital venous si nus in 14 of 24 (58%) necropsied cotton rats and in 12 of 14 (86%) wit h exophthalmos. Exophthalmos in this colony of cotton rats appears to have resulted predominantly from orbital venous sinus thrombosis cause d by stasis of venous blood secondary to right heart failure associate d with a heritable cardiomyopathy.