Heterogeneity and continuum of multiple sclerosis in Japanese according to magnetic resonance imaging findings.

There are two distinct subtypes of multiple sclerosis (MS) in Asians: optic-spinal (OSMS) and conventional (CMS). Longitudinally extensive spinal cord lesions (LESCLs) extending over three or more vertebral segments are characteristic of patients with OSMS, yet in Asians, one-fourth of CMS patients also have LESCLs. To clarify the distinction between LESCLs in OSMS and CMS, and to characterize the relationship between the presence of LESCLs and brain magnetic resonance imaging (MRI) findings, we studied 142 patients with clinically definite MS of relapsing-remitting onset and 12 patients with primary progressive MS (PPMS) by MRI of the whole spinal cord and brain. The former was diagnosed by Poser criteria, including 57 with OSMS, 67 with CMS and 18 with brainstem-spinal form of MS, while the latter by McDonald criteria. The presence of LESCLs throughout the entire clinical course was significantly more common in OSMS patients than in CMS patients, while brain lesions fulfilling the Barkhof criteria (Barkhof brain lesions) were significantly more common in CMS patients than OSMS patients. LESCLs in OSMS patients most frequently affected the upper to middle thoracic cord, with either holocord or central gray matter involvement. By contrast, 70% of LESCLs in CMS patients predominantly affected the peripheral white matter of the mid-cervical cord. LESCLs in patients with PPMS also showed preferential involvement of the peripheral white matter of the mid-cervical cord. One-third of OSMS patients had neither LESCLs nor Barkhof brain lesions more than 10 years after disease onset, and showed significantly milder disability than OSMS patients with LESCLs. These findings suggest that LESCLs are heterogeneous between OSMS and CMS patients, and that there are distinct subtypes of MS in Japanese, according to clinical and MRI findings.