Multiple sclerosis and neuromyelitis optica spectrum disorders in Malaysia: A comparison in different ethnic groups

•Important epidemiological data about the disease in Malaysia ie Multiple Sclerosis (MS) and Neuromyelitis optica spectrum disorders (NMOSD) are the two commonest demyelinating diseases seen with ratios of 1.3 to 1.0.•Important Inter-ethnic differences; NMOSD is commoner in the Chinese ethnic group while MS is commoner amongst the Indians and Malays. Seropositive NMOSD is significantly associated with Chinese NMOSD patients.•Inter-ethnic differences in terms of clinical presentation, laboratory findings and neuroimaging are described.•The importance of recognition of these differences so management of the disease can be optimized in resource limited settings. We performed a retrospective observational analytical study looking at the frequencies and characteristics of multiple sclerosis(MS) and neuromyelitis optica spectrum disorders(NMOSD) in consecutive patients with idiopathic inflammatory demyelinating disease (IIDDs) attending three centers (2009-2017). Of 523 patients with IIDDs, there were 173 patients with NMOSD and 230 patients with MS. The percentage of NMOSD: IIDDs was 33%. The percentage of NMOSD:Total MS and NMOSD cohort was 43%. Of 141 seropositive NMOSD patients, 134(95%) were from the three main ethnic groups. The percentage of seropositive NMOSD to IIDDs and to combined MS and NMOSD was 26.9% and 35% respectively. Ratios of MS to NMOSD were nearly equal at 1.3 to 1.0, reinforcing the high ratio of NMOSD to MS in Asia. Nearly half of the Chinese cohort were seropositive ie; 71/141 (50%) with the remainder being Malays; 56/141 (39.7%) and Indians; 7/141 (5%). Amongst the other indigenous groups seropositivity was seen in 2 each of Iban, Bajau, Kadazan descent as well as one of Bidayuh origin. Comparatively, seropositivity in NMOSD is commoner amongst the Chinese compared to the Malays (p ≤ 0.005) and Indians, p ≤ 0.05 with ratios as high as 10:1. In the MS group of 230 subjects, 123(53.5%) were Malays (ratio of MS:NMOSD of 2:1), 41(17.8%) were Chinese, (ratio of MS:NMOSD of 0.5:1.0) and 54 (23.5%)were Indians (ratios of MS:NMOSD of 5:1 amongst the Indians). The remainder from East Malaysia were made up of 2 each of Kadazans, Ibans and Bajaus including 3 each of Bidayuh and Eurasian descent. Comparatively, in the NMOSD and MS cohorts a female preponderance was noted more so amongst Chinese NMOSD patients, with rare familial occurrence in both but more in Malay MS/NMOSD patients. This study also highlighted some of the inter-ethnic differences