SPECIAL REPORT
There has been considerable uncertainty and confusion about the diagnosis of secondary-progressive multiple sclerosis (SPMS), which may stem in part from the MS Phenotype Group’s early efforts to define the clinical course of MS (Lublin et al. Neurology 2014; 83:278-286). In that paper, four sub-phenotypes of SPMS were described: those with active disease with disability progression (once considered to be transitional SPMS); active disease without disability progression (once considered RRMS); non-active disease with progression (once considered SPMS); and non-active disease without progression.