Keegan, B. Mark

Background: It is unclear if all patients with relapsing–remitting multiple sclerosis (RRMS) ultimately develop progressive MS. Onset of progressive disease course seems to be age- rather than disease duration-dependent. Some forms of progressive MS (e.g. primary progressive MS (PPMS)) are uncommon in population-based studies. Ascertainment of patients with PPMS from clinic-based populations can facilitate a powerful comparison of age at progression onset between secondary progressive MS (SPMS) and PPMS but may introduce unclear biases. Objective: Our aim is to confirm that onset of progressive disease course is more relevant to the patient’s age than the presence or duration of a pre-progression relapsing disease course in MS. Methods: We studied a population-based MS cohort ( n =210, RRMS n =109, progressive MS n =101) and a clinic-based progressive MS cohort ( n =754). Progressive course was classified as primary (PPMS; n =322), single attack (SAPMS; n =112) and secondary progressive (SPMS; n =421). We studied demographics (chi 2 or t -test), age-of-progression-onset ( t -test) and time to Expanded Disability Status Scale of 6 (EDSS6) (Kaplan–Meier analyses). Results: Sex ratio ( p =0.58), age at progression onset ( p =0.37) and time to EDSS6 ( p =0.16) did not differ between the cohorts. Progression had developed before age 75 in 99% of patients with known progressive disease course; 38% with RRMS did not develop progression by age 75. Age at progression onset did not differ between SPMS (44.9±9.6), SAPMS (45.5±9.6) and PPMS (45.7±10.8). In either cohort, only 2% of patients had reached EDSS6 before onset of progression. Conclusions: Patients with RRMS do not inevitably develop a progressive disease course. Onset of progression is more dependent on age than the presence or duration of a pre-progression symptomatic disease course. Moderate disability is sustained predominantly after the onset of a progressive disease course in MS.

The pathogenesis of multiple sclerosis (MS) remains elusive. Recent reports advocate greater involvement of B cells and immunoglobulins in the initiation and propagation of MS lesions at different stages of their ontogeny. The key role of B cells and immunoglobulins in pathogenesis was initially identified by studies in which patients whose fulminant attacks of demyelination did not respond to steroids experienced remarkable functional improvement following plasma exchange. The positive response to Rituximab in Phase II clinical trials of relapsing-remitting MS confirms the role of B cells. The critical question is how B cells contribute to MS. In this paper, we discuss both the deleterious and the beneficial roles of B cells and immunoglobulins in MS lesions. We provide alternative hypotheses to explain both damaging and protective antibody responses.