Heterogeneity and continuum of multiple sclerosis phenotypes in Japanese according to the results of the fourth nationwide survey

There are two distinct phenotypes of multiple sclerosis (MS) in Asians, optic-spinal MS (OSMS) and conventional MS (CMS). In 2004, we performed the fourth nationwide epidemiological survey of MS. The epidemiological features were reported elsewhere; here we report the characteristic features of patients with each MS phenotype, classified according to the clinically estimated sites of involvement and MRI findings. Among 1493 MS patients collated, 57.7% were classified as having CMS and 16.5% were classified as having OSMS. Based on MRI findings, MS patients were further subdivided into those with OSMS with or without longitudinally extensive spinal cord lesions (LESCLs) and those with CMS with or without LESCLs. Although disease duration did not differ significantly among the four groups, EDSS scores were significantly higher in patients with LESCLs than in those without LESCLs, irrespective of OSMS or CMS phenotype. Similar trends were found for the frequencies of bilateral visual loss, transverse myelitis, and marked CSF pleocytosis and neutrophilia. Increased IgG index, brain lesions fulfilling the Barkhof criteria and secondary progression were more commonly found in CMS patients than in OSMS patients, while negative brain MRIs were more commonly encountered in OSMS patients than CMS patients, irrespective of the presence of LESCLs. These findings suggest that demographic features not only vary based on CMS or OSMS phenotype, but also with the presence or absence of LESCLs, and that nonetheless, these four phenotypes constitute a continuum.