Recurrent pyogranulomatous polymyositis and intramuscular abscesses secondary to Corynebacterium species in a young beagle

Abstract

AbstractA 16‐month‐old, male, entire beagle presented for suspected relapse of steroid‐responsive meningitis‐arteritis 12 months after diagnosis. Following improvement with immunosuppressive treatment, the dog developed lethargy and right pelvic limb lameness. Neuroanatomical localisation was to the L4–S3 spinal cord segments/associated peripheral nerves. Magnetic resonance imaging revealed peripherally contrast‐enhancing, fluid‐isointense, cavitary lesions within the right and left great adductor, gracilis muscles and right semimembranosus, internal and external obturator, superficial glutaeal and coccygeal muscles. Culture and sensitivity of muscle fine‐needle aspiration revealed Corynebacterium species without antibiotic resistance. Clinical signs resolved on amoxicillin‐clavulanate (25 mg/kg/12 h) and clindamycin (20 mg/kg/12 h), but relapsed after 6 weeks. Addition of marbofloxacin (2 mg/kg/24 h) achieved clinical resolution. After 2 weeks, the dog relapsed and the owner elected euthanasia. Postmortem biopsies of the gracilis and semitendinosus muscles revealed pyogranulomatous polymyositis. Corynebacterium species should be considered a differential diagnosis for pyogranulomatous polymyositis in dogs. Lack of response to appropriate antibiotic treatment in immunosuppressed dogs may carry a poor prognosis.