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

We report a rare case of probable arteritic posterior ischemic optic neuropathy (PION) secondary to giant cell arteritis (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 bilateral visual loss and normal inflammatory markers (ESR 14 mm/hour, 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 one 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 critical importance of maintaining suspicion for arteritic etiologies and considering temporal artery biopsy even when ESR, CRP, and MRI are normal.