Masseter myodegeneration in the horse: Suggested approach to diagnosis and treatment

A descriptive case report of the management of a miniature pony presenting to a UK equine veterinary hospital with marked trismus and increased masseter muscle size. Diagnosis of masseter myodegeneration (MM) was aided by the use of computed tomography and excisional biopsy. Hyperlipaemia was diagnosed as a sequelae of MM. Treatment included nonsteroidal anti-inflammatories, parenteral nutrition and fluid therapy in addition to supportive care. The gelding was discharged from the hospital 30 days after admission, having made a full recovery. MM in the horse is a rare condition that appears to be physiologically distinct from canine masticatory muscle myositis which is primarily immune mediated.