Abstract

Background : CRION is a rare steroid-responsive optic neuropathy marked by painful, recurrent optic neuritis that flares with steroid tapering or withdrawal. It accounts for fewer than 1% of optic neuritis cases, yet carries a high risk of irreversible vision loss if untreated. Diagnosis is clinical, made after excluding multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein antibody disease (MOGAD). Early recognition and prompt therapy are essential to preserve visual function. 

Case : A 60-year-old man presented with six weeks of progressive left-eye blurred vision and periocular pain. He had a history of at least four prior episodes of bilateral visual loss over the past 12 years, each responsive to oral corticosteroids. Past medical history included blunt trauma to the right eye and throat cancer treated with chemoradiation. Clinical Examination : ● Visual acuity: initially 20/100 OS → improved to 20/40 post-treatment; hand motion OD ● Fundus: mild disc edema, both eyes; optic pallor, OD ● OCT: cystoid macular edema and epiretinal membrane OS; lamellar hole with intraretinal fluid OD Investigations : ● MRI brain/orbits/spine: bilateral intraorbital optic nerve enhancement; no demyelinating lesions ● CSF: protein 64 mg/dL, 1 WBC/mm³, negative oligoclonal bands ● Serology: AQP4-IgG, MOG-IgG, NMDA, and acetylcholine receptor antibodies all negative .

Management and Outcome : The patient was treated with high-dose IV methylprednisolone (1 g/day for 5 days), followed by a tapering course of oral prednisone. His visual acuity improved significantly in the affected eye. Given the relapsing course and steroid dependence, long-term immunosuppression with mycophenolate mofetil is being started; rituximab is reserved for future failures. Low-vision support services were also arranged. At 3-month follow-up, visual acuity remained 20/40 OS with no new relapses. Conclusion : CRION should be suspected in patients with isolated, steroid-responsive optic neuritis and negative evaluations for MS, NMOSD, and MOGAD. Timely corticosteroid therapy can result in substantial visual recovery; untreated, up to 70 % of eyes decline to ≤ 20 / 100. In patients with recurrent episodes or steroid dependence, long-term immunosuppression may be necessary to prevent further optic nerve damage. Raising awareness of CRION can reduce diagnostic delays and improve outcomes.

Learning Pearls : 1. Recurrent optic neuritis with pain and steroid dependence should raise suspicion for CRION. 2. Normal brain and spine MRI and negative AQP4/MOG antibodies are essential to diagnosis. 3. Delays in treatment may result in irreversible vision loss - act promtly. 4. After two or more relapses, initiate steroid-sparing therapy to protect vision.