Variation in MS outcome

The course of multiple sclerosis (MS) is highly variable, manifest by a wide range in age at onset, either relapsing or progressive course from onset, and major differences in attack severity and recovery.¹ Not surprisingly, the rate and age at which severe and permanent disabilities are attained are also highly variable. Most of these descriptors of outcome are generally considered independently of one another, as are the clinical and radiologic features of disease; however, certain features cluster and may define unique subtypes of CNS demyelinating disease. For example, neuromyelitis optica spectrum disorders (NMOSD), which had been traditionally considered as a type of MS, are characterized by older age at onset, relative selectivity for certain parts of the nervous system, and lack of association with a progressive course despite being associated with severe attacks.² Until it was recognized that these characteristics define a unique subtype of disease, NMOSD was included in studies of prototypic MS, thereby distorting the perceived clinical course of MS. Furthermore, because NMOSD is associated with black ancestry, spurious conclusions were made about an association of black ancestry with severe attacks and adverse outcomes of MS. Quantitative differences in MS course also associate with race/ethnicity in individuals with MS, even when patients with NMOSD are excluded. African Americans have a worse prognosis than whites³; whites have a worse prognosis than Japanese.⁴