Abstract
1. Background
Inflammatory myopathy is generally categorized into generalized inflammatory myopathies (gIM), which affect muscles throughout the body, and focal inflammatory myopathies (fIM), which are localized to specific muscles or muscle groups. This report details a case of immune-mediated polymyositis in a dog, successfully diagnosed using MRI and IHC and managed with immunosuppressive therapy.
2. Case presentation
A 5-year-old castrated male Poodle was admitted to a hospital presenting with lethargy and exercise intolerance. Biochemical analysis revealed significantly elevated serum levels of aspartate aminotransferase (AST) and creatine kinase (CK). Physical examination showed muscle atrophy in the hind legs, but further orthopedic and neurological examinations identified no additional abnormalities. MRI demonstrated hyperintense and heterogeneous signal changes across the muscles, including contrast enhancement, suggesting polymyositis. This diagnosis was confirmed through histopathological examination, which revealed inflammatory lesions with fibrous tissue proliferation within the muscle tissue.
3. Conclusions
The dog was diagnosed with immune-mediated polymyositis and treatment was initiated with prednisolone (Solondo®, Yuhan Pharmaceuticals) at 1 mg/kg twice daily and azathioprine (Immuthera®, Celltrion Pharmaceuticals) at 2 mg/kg once daily. Following the administration of these immunosuppressive agents, CK levels returned to normal, and the dog’s exercise intolerance and lethargy resolved. The thickness of the hind legs also increased progressively. The dog has maintained an improved condition under continued immunosuppressive therapy for four months. This case highlights the critical role of MRI and immunohistochemistry in diagnosing immune-mediated polymyositis, demonstrating their superiority over conventional electromyography (EMG) in this context.