Anti-aquaporin-4 antibodies in idiopathic inflammatory 9 demyelinating disorders

Abstract

Introduction: Idiopathic inflammatory demyelinating disorders (IIDD) affect the central nervous system. In classical multiple sclerosis (CMS), brain, optic nerves (optic neuritis [ON]) and spinal cord (acute transverse myelitis [ATM]) are affected. In neuromyelitis optica (NMO), optic nerves and spinal cord are predominantly affected. NMO-IgG, an antibody targeting aquaporin-4 (AQP4) water channel, is a marker for NMO. We studied the frequency and clinical relevance of anti-AQP4 antibodies seropositivity in IIDD patients. Methods: NMO-IgG was detected by indirect immunofluorescence using primate cerebellum. Results: NMO-IgG was detected in 6 of 10 NMO patients (60%), 6 of 10 idiopathic relapsing transverse myelitis (IRTM) patients (60%), 2 of 9 idiopathic relapsing optic neuritis patients (22%), 1 of 11 patients (9%) having single ON attack, 1 of 30 CMS patients (3%), and none of patients having single ATM attack or controls. Comparing NMO-IgG–seropositive (n=12) with NMO-IgG–seronegative (n=8) patients having NMO or IRTM, NMO-IgG seropositivity was associated with a higher relapse rate in the first 2 years, 1.5 and 0.6 attacks/year for seropositive and seronegative groups respectively (P=0.006), and non-significant trend towards more severe ON and myelitis with poorer clinical outcome. Conclusion: Anti-AQP4 antibodies facilitate diagnosis of NMO spectrum disorders and anti-AQP4 antibodies seropositivity is associated with higher relapse rate in the first 2 years.