Seronegative Chronic Relapsing Inflammatory Optic Neuropathy.

Chronic relapsing inflammatory optic neuropathy (CRION) is a rare cause of recurrent optic neuritis characterized by steroid responsiveness and relapse upon treatment withdrawal. Because no definitive diagnostic test exists, the diagnosis is clinical and requires exclusion of more common demyelinating and antibody-mediated disorders. We describe a 45 year-old woman with a history of psoriasis, photodermatitis, and Hashimoto thyroiditis who presented with four episodes of severe left retro-orbital pain and progressive visual blurring over a three-year period, with the right eye remaining unaffected throughout. Each episode demonstrated left optic nerve enhancement on magnetic resonance imaging and responded promptly to intravenous corticosteroids. Extensive evaluation for multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein (MOG) antibody disease was consistently negative. A diagnosis of seronegative CRION was established based on the recurrent steroid-responsive clinical pattern. Long-term immunosuppressive therapy with mycophenolate mofetil, later transitioned to mycophenolic acid due to gastrointestinal intolerance, resulted in clinical stability during follow-up. One additional relapse occurred following a brief three-day interruption of mycophenolate for treatment of cellulitis. CRION should be considered in patients with recurrent optic neuritis when workup for demyelinating and antibody-mediated conditions is negative. Early recognition and initiation of long-term immunosuppressive therapy are important to reduce relapse frequency and prevent cumulative optic nerve damage.