Masticatory Myositis of a Dog – Case Study
Abstract
Atrophic myositis is the result of prominent atrophy of masticatory muscles. The masseter, temporal, and pterygoid muscles are selectively affected. A dog was presented to the Emergency Clinic of our Veterinary Faculty with the following clinical signs: progressive dyspnea and weight loss, apathy, cough, adinamia. The 11 years old, female, crosss-breed dog was reported to be unable to completely open his mouth (trismus), with the head having a fine fox-like contour, with unusual prominences of zygomatic arches. Following necropsy, the gross exam revealed advanced bilateral atrophy and fibrosis of temporal, pterigoid and masseter muscle, accompanied by a primary mammary carcinoma with pulmonary metastases. Histological lesions from the masticatory muscles were very patchy. In some areas there was an admixed inflammatory infiltrate predominately composed of lymphocytes and plasma cells. Muscle fiber atrophy was associated with focal areas of chronic proliferative fibrosis. In conclusion, masticatory muscle myositis needs to be included in the differential diagnosis of disorders in dogs with trismus and abnormal jaw function.
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