Neuromyelitis optica‐IgG in idiopathic inflammatory demyelinating disorders amongst Hong Kong Chinese

Background:  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 autoantibody targeting aquaporin‐4, is a marker for NMO. We studied the frequency and clinical relevance of NMO‐IgG seropositivity in IIDD patients.Methods:  Neuromyelitis optica‐IgG was detected by indirect immunofluorescence using primate cerebellum.Results:  Neuromyelitis optica‐IgG was detected in six of 10 NMO patients (60%), six of 10 idiopathic relapsing transverse myelitis (IRTM) patients (60%), two of nine idiopathic relapsing ON patients (22%), one of 11 patients (9%) having single ON attack, one 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 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:  Neuromyelitis optica ‐IgG facilitates diagnosis of NMO spectrum disorders. NMO‐IgG seropositivity is associated with higher relapse rate in first 2 years.