両眼性複視を伴った特発性眼窩筋炎に対して下直筋後転術が奏効した1例

A case of idiopathic orbital myositis with binocular diplopia in which inferior rectus muscle recession provided favorable outcomes

要約　目的：眼窩を中心とした原因不明の良性かつ非感染性炎症性疾患である特発性眼窩炎症のうち，外眼筋の炎症が病態と考えられるものを特発性眼窩筋炎という。今回筆者らは，慢性期の特発性眼窩筋炎に対して罹患眼の下直筋後転術が奏効した症例を経験したので報告する。

症例：75歳，男性。両眼性複視を認め，前医で頭部MRIを施行したが原因不明のため獨協医科大学埼玉医療センター眼科に初診となった。前眼部，中間透光体，眼底ともに炎症を含め特記事項はなかった。交代プリズム遮閉試験による眼位検査で左眼固視にて20△右下斜視，ヘス赤緑試験で右眼の上転障害を認めた。眼窩部MRIおよび血液検査から原因不明の特発性眼窩筋炎と診断した。治療に際して患者は副腎皮質ステロイド内服加療を希望しなかったこと，また第1眼位で上下斜視を認めたことから手術適応と判断し，右眼下直筋に対して下直筋後転術を実施した。手術直後，軽度の複視症状は残存するも眼球運動は改善しており，手術2か月後には複視症状は消失した。

結論：本症例の経過から慢性期の特発性眼窩筋炎に対して斜視手術は複視症状を改善させる可能性がある。

Abstract　Introduction：Idiopathic orbital myostisis, a benign, noninfectious inflammatory disease of unknown cause centered in the orbit, caused by inflammation of the external ocular muscles. We report a case of chronic idiopathic orbital myositis that was successfully treated by recession of the inferior rectus muscle of the affected eye.

Case：A 75-year-old man presented to our department for the first time because with binocular diplopia, the cause of which was unknown following a head MRI scan at his previous doctor. There were no special findings, e.g. inflammation in the anterior, intermediate translucency, or fundus of the eye. Eye position examination with an alternate prism cover test showed 20△ right inferior obliquity with left eye fixation, and supraduction disability of the right eye was observed with the HESS red-green test. Based on orbital MRI and blood tests, the patient was diagnosed with idiopathic orbital myositis of unknown origin. Since the patient did not wish to receive oral corticosteroids treatment for his symptoms. Because of vertical strabismus in the first eye position, the patient was judged to be suitable for surgery. Accordingly, a 5 mm inferior rectus recession was performed on the inferior rectus muscle of the right eye. Immediately after surgery, eye movements improved, although mild diplopia remained, until 2 months after the surgery, after which it disappeared.

Results：Based on the course of this case, strabismus surgery for idiopathic orbital myositis may ameliorate diplopia.