Objective: To estimate the frequency and prognostic value of NMO-IgG seropositivity in patients presenting with isolated optic neuritis (ON) and no prior neurological events. Background: The aquaporin-4-specific autoantibody, NMO-IgG, is a biomarker for neuromyelitis optica (NMO). We have shown that 38% of patients with longitudinally extensive transverse myelitis (LETM) and 20% of recurrent ON are seropositive and are at high risk for recurrence of ON and myelits. The frequency and prognostic significance of seropositivity in individuals with isolated ON are unknown. Design/Methods: Medical records of all patients evaluated clinically at Mayo Clinic, Rochester-MN (MCR) for whom NMO-IgG testing was requested from January 2005 through December 2007 were reviewed. We excluded patients referred to MCR following identification of NMO-IgG seropositivity from the frequency analysis. We obtained follow-up data by telephone interview. Results: Of 583 patients clinically evaluated at MCR on whom NMO-IgG was ordered, 23 (3.4%) had a clinical diagnosis of isolated ON. One patient (4.3% of those with isolated ON who were tested) was seropositive. Five additional patients were referred to Mayo Clinic (2005-2008) because of seropositivity for NMO-IgG test after isolated ON. After a mean (SD) follow-up of 2.72 years (3.78), 1/22 (4.5%) of the seronegative and 3/6 (50%) of the seropositive group experienced and additional relapse of ON and/or LETM (p=0.01). Conclusions/Relevance: The frequency of NMO-IgG seropositivity in a consecutive series of patients seen at MCR with first ON for whom NMO-IgG was ordered was low; presumably, referral for testing for NMO-IgG was biased for risk factors for NMO (e.g. bilateral or more severe ON), thus the frequency in an unbiased series may be lower. Nonetheless, seropositive individuals are at higher risk of severe attacks of ON or LETM. Prophylactic immunosuppression of NMO-IgG seropositive individuals, regardless of the presenting syndrome, is indicated.
Read More: The prognostic value of neuromyelitis optica-IgG in isolated optic neuritis