EN
Muscle diseases belong to uncommon diseases in small animals. According to the literature an idiopathic form of that process may be reported as dermatomyositis, eosinophilic myositis and polymyositis. Whereas dermatomyositis and eosinophilic myositis occur mostly in Ehrlichia canis infected dogs and are restricted to masticatory and neck muscles, polymyositis is a generalised disease and the lesions appear in skeletal and heart muscles. In our case the presence of rickettsia was not confirmed and it was of idiopathic origin. Because of its character the process (infiltration of round cells, necrosis, colagenisation) seemed to be caused by immune response of the animal.