A three-dimensional approach for understanding the spectrum of idiopathic inflammatory demyelinating disorders: importance of the 'attack-related severity' axis

Understanding the spectrum of idiopathic inflammatory demyelinating disorders (IIDD) of the central nervous system is an important issue for accurate diagnosis and advancing research on the pathogenesis as well as treatment strategies, but the nosology and the classification of the IIDD remains confusing. Until now, we have tried to apply each disorder within the spectrum to an adequate co-ordinate on a two-dimensional plane. One axis is clinical course and the other is lesion distribution. We reviewed some disorders of the IIDD spectrum, and our recent findings on the fulminant nature of each attack and the expansion of each lesion, which we called attack-related severity in Japanese multiple sclerosis (MS). From our findings and the literature, attack-related severity appears to be a third important factor, in addition to lesion distribution and clinical course. Introduction of the third axis produces a three-dimensional space for a better understanding of the heterogeneous characteristics of IIDD and 'MS' syndrome, and can advance treatment strategies for these disorders. As severe attacks seem to be relatively common in Asians but rare in the west, ethnic-related heterogeneity should be considered in understanding the spectrum of IIDD, and there is an urgent need to develop a common general concept of the spectrum, especially for MS.