NMO-IgG in idiopathic inflammatory demyelinating disorders among Hong Kong Chinese

Abstract

Objective: Neuromyelitis optica (NMO) is characterized by monophasic or recurrent attacks of acute transverse myelitis (ATM) and optica neuritis (ON). 73 % of Caucasian NMO patients are seropositive for the NMO-IgG which distinguishes NMO from classical multiple sclerosis (CMS). The NMO-IgG autoantigen is aquaporin-4 water channel. We aim to study the seropositivity rate of NMO-IgG in local patients with idiopathic inflammatory demyelinating disorders (IIDD). Methods: Local IIDD patients (CMS, ATM [single or recurrent] without ON, ON [single/recurrent] without ATM, ATM with ON [monophasic or recurrent], acute disseminated encephalomyelitis [ADEM]) had sera taken at onset. Control sera were from healthy subjects, and patients with other neurological disorders (OND: stroke, Gullain-Barre syndrome, polymyositis, paraneoplastic neurological disorders).CMS was diagnosed according to revised McDonald’s criteria. Patients were followed up for at least 1 year. Sera from IIDD patients and controls were tested for NMO-IgG by indirect immunofluorescence using slides containing Monkey cerebellum and mouse gut tissues. Rabbit anti-aquaporin 4 antibody (Sigma) was used for positive control. Results: Three of 5 (60 %) non-CMS patients with ATM and ON were NMO-IgG positive. All 5 had extensive ATM, 4 of the 5 had severe visual impairment or paraplegia. Two of the 5 had brainstem dysfunction clinically with brainstem abnormalities on magnetic resonance imaging (MRI) brain; MRI brain was otherwise normal for all 5. All 5 were negative for cerebrospinal fluid oligoclonal bands.One of 25 (4 %) CMS patients was seropositive for NMO-IgG. Among 5 patients with recurrent ATM without ON, 3 were NMO-IgG positive and all 3 had recurrent extensive ATM (> 3 vertebral segments on MRI spine); one of the 2 NMO-IgG negative patients had recurrent extensive ATM with brainstem involvement, and one had recurrent ATM extending < 3 vertebral segments. None of patients with a single attack of ATM (8) or single/recurrent ON (11)were seropositive for NMO-IgG. None of the healthy subjects or patients with OND was NMO-IgG positive. Two patients with paraneoplastic cerebellar ataxia and breast cancer were seropositive for the Purkinje cell antibody type 1 (anti-Yo). Conclusion: 60 % of local patients with NMO or recurrent extensive ATM without ON were seropositive for NMO-IgG, while 4 % of CMS patients were seropositive. NMO-IgG is useful for diagnosis of NMO and recurrent extensive ATM without ON.