Incidence of giant cell arteritis mimicking non-arteritic anterior optic neuropathy

Purpose: Giant cell arteritis (GCA) involving ophthalmic circulation often manifests as anterior ischemic optic neuropathy (AAION), presenting with severe vision loss and pallid optic disc edema. Non-arteritic anterior ischemic optic neuropathy (NAION) classically presents with segmental optic disc edema and corresponding altitudinal visual field defect (VFD) with small cup-to-disc ratio in the fellow eye. Differentiating these two entities is critical as GCA requires immediate treatment to prevent vision loss in the fellow eye. This study investigated how often GCA mimics NAION at presentation. Methods: Retrospective chart review of patients with temporal artery biopsy (TAB) positive GCA with ocular manifestations seen at a tertiary neuro-ophthalmology practice between 2015 and 2020. Patients presenting with segmental non-pallid optic disc swelling and corresponding altitudinal VFD mimicking NAION were identified. Results: The clinical presentation of 7.1% (3/42) of patients with TAB-positive GCA mimicked NAION. Two of three patients had cup-to-disc ratio of <0.3 in the fellow eye. Two patients were women, mean age was 67.3 +/- 6.5 years, and mean presenting visual acuity was 0.45 +/- 0.48 LogMAR. Two patients had a normal temporal artery ultrasound. Two of three patients had at least one systemic symptom of GCA at presentation and all had elevation of one or both inflammatory markers. Conclusions: There should be high index of suspicion for GCA, even in patients highly suspected to have NAION. Inflammatory markers must be checked in every patient with presumed NAION and TAB performed if one or both are elevated to avoid missing GCA.