Severe polymyositis and neuritis in a cat

Abstract

A 4-year-old domestic shorthair cat was evaluated for a 1-week history of shifting limb lameness that progressed to tetraparesis. Physical examination revealed generalized muscle atrophy and signs of discomfort when the muscles of the appendicular skeleton were palpated. Neurologic examination revealed diminished myotatic and withdrawal reflexes in all 4 limbs. Results of a CBC indicated mild neutrophilia, and serum biochemical analysis revealed mild hyperalbuminemia and high creatine kinase activity. The cat was anesthetized, and an electromyogram (EMG), CSF sample, and nerve and muscle biopsy specimens were obtained. The EMG revealed positive sharp waves and fibrillation potentials, CSF analysis revealed albuminocytologic dissociation, and histologic examination of muscle and nerve specimens revealed severe myositis and neuritis. Immune-mediated polymyositis and neuritis were suspected. With physical therapy and long-term corticosteroid drug treatment, the cat recovered complete motor nerve function. The severity and rapid progression of clinical signs, combined with the EMG abnormalities and histologic findings, could have led to inappropriate euthanasia for this cat. Veterinarians should be aware that immune-mediated polymyositis and neuritis in cats can have an excellent prognosis with appropriate, long-term treatment.