Prevalence of, and Disability Due to, Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder in Japan by the Fifth Nationwide Survey.

Background and objectives: All 4 previous nationwide surveys of multiple sclerosis (MS) in Japan were conducted before the discovery of anti-aquaporin-4 (AQP4) antibodies; thus, neuromyelitis optica spectrum disorder (NMOSD) was included in MS, as optic-spinal MS. We aimed to clarify the epidemiologic features and trends of MS and NMOSD in Japan separately using a fifth nationwide survey.

Methods: The primary survey, in which a questionnaire was sent to 3,799 selected departments (including neurology/internal medicine, pediatrics, and ophthalmology), explored the estimated number and prevalence of patients with MS or NMOSD in 2017, and the secondary survey collected detailed characteristics of the patients using a second questionnaire.

Results: The response rates for the primary and secondary surveys were 60.1% and 53.9%, respectively. The estimated total number of patients with MS or NMOSD was 24,800, 2.5-fold higher than that in the fourth survey in 2003. The crude prevalence was 19.6 per 100,000 patients (14.2 for MS and 5.4 for NMOSD), compared with 7.7 per 100,000 patients in the fourth survey. Patients with MS showed milder disability (median Expanded Disability Status Scale [EDSS] score: 2.0 [interquartile range 1.0-4.5] vs 2.5 [1.0-6.0]), decreased secondary progression (8.5% vs 15.2%), and increased usage of disease-modifying drugs (63.7% vs 37.2%) compared with those with conventional MS in the fourth survey. The proportions of oligoclonal bands and Barkhof criteria fulfillment on MRI, which are features of classical MS, increased with advancing year of birth. Patients with NMOSD also showed less disability and shorter disease duration than patients with optic-spinal MS in the fourth survey (EDSS score: 3.5 [2.0-5.5] vs 3.8 [2.0-6.0]; disease duration: 8.0 [3.9-14.8] vs 10.0 [5.0-16.0]). Among patients with NMOSD, disability was exacerbated by a history of longitudinally extensive spinal cord lesions and anti-AQP4 antibody positivity, which both decreased with advancing year of birth.

Discussion: The prevalences of MS (particularly with classical features) and NMOSD have been increasing in Japan, suggesting the contribution of environmental factors. However, disabilities in patients with MS and NMOSD have been mitigated. Extensive usage of various disease-modifying drugs could be a factor contributing to this disability mitigation in MS.