Miosite crônica dos músculos mastigatórios em cão sem raça definida : relato de caso

Abstract

Masticatory muscle myositis (MMM) is an immune-mediated inflammatory myopathy affecting dogs, characterized by autoantibodies against type 2M muscle fibers. Clinically, it presents with trismus, pain, and inflammation in the acute phase, potentially progressing to muscular atrophy and fibrosis in the chronic stage. Diagnosis is based on the correlation between clinical history, laboratory findings, and histopathological analysis of the affected muscle, which reveals inflammatory infiltrate and structural alterations. This report describes the case of a two-year-old mixed-breed female dog presenting with trismus and muscle atrophy. After hematological and histopathological examinations, MMM was diagnosed, and treatment with prednisolone (2 mg/kg BID) was initiated, resulting in clinical remission within 10 days, recovery of masticatory function, and reduction of trismus. The protocol included gradual tapering over 42 days. However, after six and ten months, clinical relapses occurred and were again treated with prednisolone. In the second relapse, cyclosporine was recommended, but due to cost, the owner did not obtain it, continuing with prednisolone alone, which again led to remission. This case highlights the recurrent nature of MMM and emphasizes the importance of early recognition, immunosuppressive therapy, and continuous veterinary monitoring to minimize clinical signs and maintain quality of life in affected dogs.