A secondary progressive clinical course is uncommon in neuromyelitis optica.

We compared the clinical course of 96 patients with neuromyelitis optica (NMO) to multiple sclerosis (MS) natural history data. Based on the distribution of follow-up data (median 6.1 year), we estimated that 21 NMO patients would convert to a secondary progressive course, but we observed only two conversions (p = 0.00002; relative risk = 0.08). The disparate natural histories of MS and NMO suggest dissociation between relapses and clinical progression in CNS demyelinating diseases.