視神経周囲炎による視力低下をきたした甲状腺眼症の1例

Optic perineuritis with visual impairment in a case of thyroid ophthalmopathy

要約　目的：視神経周囲炎により視力が低下した甲状腺眼症の1例の報告。

症例：71歳女性に複視が突発した。その翌日から右眼視力が低下し，8日後に受診した。

所見と経過：矯正視力は右0.04，左1.2で，右眼に外転制限があり，内斜視であった。右眼のRAPDは陽性で，右限界フリッカ値は大きく低下していた。眼底に著変はなかった。血液の抗サイログロブリン抗体と抗ペルオキシダーゼ抗体が陽性であった。眼窩MRIで，造影T1強調画像の軸位断で右内直筋の筋腹に高度な肥大と炎症の所見があり，右視神経の周囲に造強効果がある視神経周囲炎があった。冠状断では，右内直筋と下直筋の炎症が眼窩先端部に及んでいた。メチルプレドニゾロンによるミニパルス療法で，3日後の1クール終了時に右矯正視力は0.9に回復し，2クール後には右眼の眼球運動制限も改善した。

結論：本症例での視神経周囲炎は，甲状腺眼症に伴う外眼筋の炎症が眼窩先端部から視神経周囲に波及したと推定される。

Abstract　Purpose：To report a case of thyroid ophthalmopathy who developed sudden visual loss due to optic perineuritis.

Case：A 71-year-old woman noted sudden visual impairment in her right eye. She developed diplopia the following day and was seen by us one week later.

Findings：Best corrected visual acuity was 0.04 in the right eye and 1.2 in the left eye. The right eye showed limited abduction with esotropia. Relative afferent pupillary defect was positive and critical flicker frequency was severely decreased in the right eye. Antibodies to anti-thyroglobulin and anti-peroxidase were positive by hematological studies. Contrast-enhanced magnetic resonance imaging showed marked hypertrophy in the muscle belly with signs of inflammation in the medial and inferior rectus muscles in the right eye. Axial and coronal sections showed enhanced right perioptic nerve lesion. Mini-pulse therapy with methylprednisolone was followed by improvement of right best corrected visual acuity to 0.9. Impaired eye movement with diplopia disappeared after two sessions of mini-pulse therapy.

Conclusion：Optic perineuritis in the present case appears to have developed secondary to severe inflammation in extraocular muscles due to thyroid ophthalmopathy that extended to the orbital apex and optic nerve.