Probable Arteritic Posterior Ischemic Optic Neuropathy with Atypical Recovery Secondary to Biologically Occult Giant Cell Arteritis: A Case Report.

Posterior ischemic optic neuropathy (PION) is a rare form of ischemic optic neuropathy, and arteritic PION secondary to giant cell arteritis (GCA) usually has a poor prognosis. We report a rare case of probable arteritic PION secondary to GCA with an atypically slow course and remarkable visual recovery. A 66-year-old man under mild chronic immunosuppression for autologous bone marrow transplantation presented with progressive visual loss and normal inflammatory markers (erythrocyte sedimentation rate [ESR] 14 mm/h, C-reactive protein [CRP] 1.10 mg/L). Contrast-enhanced orbital and cerebral MRI showed no vasculitic or perioptic abnormalities. Despite the atypical presentation, temporal artery biopsy performed 10 days after high-dose corticosteroid initiation confirmed healed GCA. The patient experienced major recovery of central vision (visual acuity 0.9) after 1 month of treatment. This case highlights the diagnostic challenge of biologically and radiologically silent GCA, the potential modifying role of chronic immunosuppression on disease course and recovery, and the importance of maintaining suspicion for arteritic etiologies and considering temporal artery biopsy even when ESR, CRP, and MRI are normal.