A 23-year-old female patient with severe trismus caused by myositis ossificans progressiva was reported. Her trismus developed at the age of 14 and it progressed gradually. At 15 years of age she was diagnosed myositis ossificans progressiva by orthopedists.
On admission a maximum interincisal opening of 0.5 mm was noticed but mobility of bilateral masseter muscles was not remarkably disturbed. The routine hematological studies including alkaline-phosphatase revealed normal. Computed tomograms showed the bridging of high-density mass between the right coronoid process and the zygoma, and it was diagnosed as heterotopic ossification of the insertion of the right temporal muscle.
Judging from the past medical history that her symptoms were resistent to administration of diphosphonate (EHDP) and adrenal cortical hormones and that she was not in the active state of disease then, surgical treatment of bilateral coronoidectomy and excision of calcified mass in the right temporal muscle was carried out. An interincisal opening of 30 mm was achieved at the time of the operation. The postoperative course was uneventful except that trismus developed again because of poor physiotherapy. One year after the operation, X-ray examination revealed no recalcification in the operated location.
