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P0452 - Continued increase of multiple sclerosis and neuromyelitis optica and the north-south gradient in Japan; updates from the 5th nationwide survey (ID 775)
In Japan, nationwide survey for multiple sclerosis (MS) including neuromyelitis optica spectrum disorders (NMOSD) has regularly been conducted since 1972, and the past 4 surveys conducted before the discovery of anti-aquaporin 4 antibodies demonstrated the rapid increase of MS.
To investigate the epidemiological characteristics of MS and NMOSD in Japan simultaneously through the 5th nationwide survey.
Preliminary survey was conducted to ascertain the approximate number of patients with either MS (pwMS) or NMOSD (pwNMOSD) who had seen at the selected facilities in 2017. Preliminary survey packages were sent to departments of neurology, internal medicine, ophthalmology, and pediatrics, at the facilities randomly selected using pre-determined sampling rates stratified based on the hospital bed counts. Secondary questionnaire was sent to the facilities with the cases to collect the detailed clinical information of each patient.
Out of 3,799 departments where we sent preliminary survey, 2,284 (60.1%) replied and 645 departments reported the presence of the patients with the diseases. Second questionnaire form was sent to the 645 departments for 13,067 cases, and 6,990 (53.5%) forms were returned for further analysis. Estimated number of pwMS and pwNMOSD were 24,118 in total, which is more than 10-fold higher than that (2,280) of the 1st survey in 1972. The crude prevalence for both MS and NMOSD was 19.6/100,000 (14.3 for MS and 5.3 for NMOSD). Male: female ratios of MS and NMOSD were 1: 2.2 and 1: 4.1, respectively. The onset ages (mean ± standard deviation, year) of MS and NMOSD were 32.3 ± 11.6 and 44.2 ± 16.1, respectively. The Expanded Disability Status Scale scores and disease durations were 2.7 ± 2.4 in 12.9 ± 9.0 years for MS and 3.7 ± 2.4 in 10.9 ± 9.5 years for NMOSD. Disease-modifying therapy had been used for 77.2% in MS. The proportion of pwNMOSD against pwMS was 1: 0.37. Based on the prefectures at birth, the distribution of pwMS demonstrated north-south gradient (ρ = 0.39, p = 0.008), although no significant gradient was observed in pwNMOSD. Based on the registered sites, the proportion of pwMS among both pwMS and pwNMOSD showed north-south gradient (ρ = 0.4, p = 0.004).
As the combined prevalence of MS and NMOSD was 7.7/100,000 in the 4th survey (4.4 for conventional MS and 3.3 for others including opticospinal form), the prevalence of both MS and NMOSD appears to be still increasing. Disease severity may have become milder in MS and NMOSD compared with the 4th survey (3.5 ± 2.9 in conventional MS and 4.3 ± 2.7 in opticospinal form), though the disease durations in the two studies were comparable. Higher latitude is a risk for MS but not NMOSD in Japanese.