Vascular alterations and degranulation of eosinophil leucocytes in bovine eosinophilic myositis

Histopathological examination was made on affected skeletal muscles from 10 cases of spontaneous eosinophilic myositis in Japanese Black cattle. Prominent regressive lesions with increased connective or adipose tissues were observed in affected skeletal muscles of all cases and also in the tongue, diaphragm and myocardium of a few cases. Small arteries or arterioles in muscular lesions showed edematous swelling of the intima, degeneration of the media and cellular infiltration. Infiltration of eosinophils, lymphocytes and plasma cells was remarkable with some neutrophils, while neither basophils nor mast cells appeared. Interestingly, degranulation of infiltrated eosinophils was encountered frequently accompanying eosinophilia in local lymph nodes, suggesting allergic basis in pathogenesis of the disease. Neither parasites, common bacteria, mycoplasmas nor viruses were detected, while a few sarcosporidial cysts without any reactions were seen in muscle fibers of 4 cases.