[A case of acute masticatory muscle myositis successfully treated with corticosteroids].

CASE: An 84-year-old woman. She developed a fever (37-38°C) on April X-9, 2021, and took antipyretics and analgesics, but did not improve. She developed temporal pain and eyelid edema on April X-3, which worsened, so she visited our department on April X.

MEDICAL HISTORY: She was undergoing treatment for ulcerative colitis. At the initial visit, her body temperature was 38.7°C, her face was edematous (right dominant), and her mouth was restricted. There was tenderness in the temporal region, but there was no engorgement of the temporal artery. Neurologically, there were no abnormalities in the cranial nerves, limb motor, or sensory systems. There were no signs of meningeal irritation.

EXAMINATION: Peripheral blood CRP 26.5 ‍mg/dl, WBC 12,900/mm3, RF positive (260 IU/ml), anti-galactose-deficient IgG antibody positive (146 AU/ml), anti-CCP antibody negative, and CK was within the normal range. There were no abnormalities in the temporal artery ultrasound examination. MRI-T1WI showed swelling of both temporal and masseter muscles, and STIR high intensity signal (right dominant). Symptoms and MRI findings improved promptly after oral administration of 30 ‍mg/day prednisolone. Based on the above, the patient was diagnosed with acute masticatory muscle myositis. Reports of acute masticatory muscle myositis in humans are rare.