一側の咀嚼筋に発症した限局性筋炎症例

A case of focal myositis in unilateral masticatory muscles

はじめに

　炎症性筋疾患では多発性筋炎や皮膚筋炎が代表的であるが，特殊なものとして限局性筋炎がある。限局性筋炎は，身体の一側の骨格筋に限局的な腫脹と疼痛を示す筋の特発性炎症性疾患で，下肢に限局的な疼痛や腫脹を示すことが多く，頭頸部での発症は稀とされている。今回われわれは，一側の咀嚼筋に発生した限局性筋炎の症例を経験したので報告する。

　Focal myositis is an idiopathic inflammatory myopathy that shows focal swelling and pain of the unilateral skeletal muscle, and it is rare in the head and neck region. An 86-year-old man was referred to our hospital complaining of swelling and pain of the cheek. In the magnetic resonance imaging（MRI）scan, inflammation was localized in the masseter and pterygoid muscles. After a bacterial infection, vascular accident, and tumor lesion were excluded focal myositis was finally diagnosed. These symptoms dramatically improved with administration of steroids. Because focal myositis occasionally evolves to polymyositis, we have been monitoring the patient.