Masticatory muscle myositis

Symptoms of acute MMM include swelling of the jaw muscles, drooling, and pain on opening the mouth.

Ophthalmic signs may include third eyelid protrusion, red eyes, and exophthalmos (protruding eyeballs).

The immune system recognizes these proteins as foreign to the body and attacks them, resulting in inflammation.

False negatives by the 2M antibody assay may be obtained if MMM is end-stage with destruction of type 2M fibers and marked fibrosis.

Treatment is usually with corticosteroids such as prednisone, often with decreasing doses for up to 4–6 months, and in the case of trismus, manual opening of the mouth under anesthesia.