眼窩蜂窩織炎との鑑別が困難であった後部強膜炎型特発性眼窩炎症

A case of idiopathic orbital inflammation with posterior scleritis simulating orbital cellulitis

要約　目的：眼窩蜂窩織炎に類似した臨床像を呈し，鑑別に苦慮した後部強膜炎型特発性眼窩炎症（IOI）の症例を報告すること。

症例：25歳，男性。右上眼瞼腫脹と疼痛が出現し，他院で眼窩蜂窩織炎と診断された。抗菌薬内服で改善しないため，当院を受診した。初診時の右矯正視力は1.2。右上眼瞼発赤腫脹と眼球突出，CRP値の軽度上昇（0.45mg/dl）と造影CT所見から眼窩蜂窩織炎と診断し，抗菌薬の全身投与を開始したが効果はなかった。その後，視神経乳頭発赤腫脹，網膜下液，脈絡膜皺襞，強膜充血と強膜肥厚が出現し，歪視と視力低下（0.3）が生じ，11日目には37.4℃の熱発とともにCRPが1.80mg/dlに上昇した。経過から診断を後部強膜炎型IOIに見直し，治療法をステロイド内服に切り替えたところ，所見の著明な改善がみられ，視力は1.2に回復した。

結論：本症例は治療開始時点には眼窩蜂窩織炎に矛盾しない病態を呈したが，治療経過中に後部強膜炎型IOIの診断に至った。CRPが0.43mg/dl以上であれば眼窩蜂窩織炎の可能性が高いとの既報があるが，本症例はその基準に合致せず，両者の鑑別には注意を要する。

Abstract　Purpose：To report a case of idiopathic orbital inflammation（IOI）with posterior scleritis that showed clinical features resembling orbital cellulitis.

Case：A 25-year-old male was referred to our hospital after failure in treatment for presumed orbital cellulitis of his right eye using oral and topical antibiotics.

Findings and Clinical Course：His right eye was diagnosed as orbital cellulitis based on the clinical features including swollen eyelid, exophthalmos, CT scan and elevated C-reactive protein（CRP）level（0.45 mg/dl）. He was treated with intravenous injection of antibiotics. During treatment, corrected visual acuity fell from 1.2 to 0.2, while swollen optic disc, exudative subretinal fluid, choroidal folds and thickening of sclera appeared as new findings, together with the elevated temperature（37.4℃）and further elevation of CRP（1.80 mg/dl）. These observations indicated that the diagnosis should have been IOI with posterior scleritis, and we changed the treatment method to oral corticosteroid. Subsequently, the ocular conditions improved and the visual acuity recovered to 1.2.

Conclusion：Differential diagnosis between orbital cellulitis and IOI is sometimes confusing. Even if inflammatory lab data such as elevated CRP suggest presence of orbital cellulitis, IOI should be considered when systemic antibiotics has turned out ineffective.