The clinical features of MS in Japanese are said to be characterized by high incidence of optico-spinal MS (OS-MS), although the frequency of it has recently decreased. The term OS-MS is used to describe a subgroup of patients diagnosed with MS, in which the clinically determined lesions are confined to the optic nerves and the spinal cord. The OS-MS is characterized by a female preponderance, a later onset, a higher score of the expanded disability status scale of Kurtzke (EDSS), milder abnormalities on brain MRIs, higher sero-positive rates for some autoantibodies, and higher cell counts and protein levels in the cerebrospinal fluid, compared with conventional MS. The OS-MS is positively associated with HLA-DPB1*0501 allele, and the HLA prohile are different between OS-MS and conventional MS. Therefore, the OS-MS is immunogenetically as well as clinically a distinct subtype of MS.
