Features of anti-aquaporin 4 antibody-seronegative Thai patients with neuromyelitis optica spectrum disorders: a comparison with seropositive cases.

OBJECTIVE The aim of this study is to investigate the unique features of seronegative neuromyelitis optica spectrum disorders (NMOSD) in Thailand. BACKGROUND It remains unknown whether seronegative NMOSD patients possess clinical and paraclinical features that are distinct from those with seropositivity. METHODS In a Thai cohort of idiopathic inflammatory CNS disorders (n=122), 52 patients fulfilled the Wingerchuk 2007 criteria for NMOSD. We determined anti-AQP4 antibody statuses using three different assays (an in-house cell-based assay [CBA], a commercially available CBA and a tissue-based indirect immunofluorescence [IIF] assay). RESULTS Among the NMOSD patients, the percentage of seropositive cases was 54.5% based on the in-house and commercial CBAs and 30.8% based on the IIF assay. Using the in-house CBA, seronegative NMOSD patients exhibited distinct features compared with seropositive patients, such as a lack of female preponderance (F/M=1.2 vs. 6.0), frequent simultaneous bilateral optic involvement (33.3% vs. 0.04%), a lower annual relapse rate (0.4 ± 0.3 vs. 0.7 ± 0.6), fewer spinal cord lesions (1.0 ± 4.3 vs. 1.4 ± 0.6), and lower CSF cell counts (20 ± 72 vs. 80 ± 285). Use of the commercial CBA yielded essentially similar results, but some of these differences were not significant using IIF. CONCLUSIONS Sensitive anti-AQP4 antibody assays reveal features of seronegative NMOSD patients that differ from those of seropositive patients from Thailand.