Eosinophilic Polymyositis in a Mouse

CONTEMPORARY TOPICS © 1998 by the American Association for Laboratory Animal Science 94 The term eosinophilic myositis or polymyositis is used to describe a diverse, heterogeneous group of diseases in human beings and animals. One form of the disease may be associated with parasites that invade muscle tissue, such as Trichinella or Sarcocystis (1–4). In human beings, it has been described as a reaction to drugs (5) or nutritional supplements, as has occurred with particular suppliers of L-tryptophan (6, 7). Eosinophilic myositis also occurs as a disease of unknown origin (idiopathic eosinophilic polymyositis) (1, 8–12). In human beings, idiopathic eosinophilic myositis can occur as a localized lesion (9, 13) and has even been described as a pseudotumor (14), or as a generalized condition involving multiple skeletal muscles and the heart (8, 9, 11). The disease can occur with or without concurrent increase in the number of eosinophils in the peripheral blood (9, 11, 15). A form of idiopathic eosinophilic myositis has been described in dogs (16), in which the lesions are frequently confined to the muscles of mastication, but cases of generalized disease have also been described (16). This report describes a case of eosinophilic polymyositis involving skeletal as well as cardiac muscle in a mouse.