Disorders of the muscles of mastication occur relatively commonly in clinical practice and can be of myopathic or neuropathic origin. Masticatory muscles are predominantly composed of fibres designated as Type 2M. Masticatory muscle disorders (MMD) can be diagnosed by the assay of serum from affected animals to see if there are autoantibodies against Type 2M fibres.

False negative results may be obtained if immunosuppressive dosages of corticosteroids have been given for longer than 7 – 10 days in end-stage masticatory muscle myositis and in polymyositis. A muscle biopsy would be necessary for confirmation of the diagnosis in these cases.

A 1mL serum sample is required.