BACKGROUND: Multiple sclerosis (MS) is the most common demyelinating disease, and onset over the age of 50 years is referred to as late onset MS (LOMS). It has been thought that LOMSers will be more likely to exhibit a primary progressive (PPMS) clinical course.
OBJECTIVE: To identify the clinical characteristics of demyelinating disease in patients over the age of 50 years from four different MS centres in the Northern Midwest USA.
METHODS: We reviewed medical records of all MSers seen at the MS centres and identified those who were 50 years of age or more at the time of first spontaneously reported symptoms. We included those who were diagnosed with MS or clinically isolated syndrome (CIS) and excluded MS mimickers. Demographics, initial clinical course diagnosis, clinical characteristics, and any available five-year follow up data were collected. The clinical course was re-evaluated in each MSer with careful questioning regarding any prior focal neurological symptoms that had persisted for at least 48h, not otherwise explained. Those with a prior event who were initially diagnosed with PPMS or CIS were reclassified as secondary-progressive MS (SPMS) and relapsing-remitting MS (RRMS) respectively.
RESULTS: We identified 124 MSers from a total of 3700 patients, making LOMS 3.4% MS in our population. The initial clinical course was RRMS in 50 (40%), PPMS in 44 (36%), SPMS in 15 (12%), and CIS in 15 (12%) patients. After reclassification the clinical course was RRMS in 55 (44%), PPMS in 25 (20%), SPMS in 34 (28%), and CIS in 10 (8%) of patients. The clinical syndrome was identified as acute for 77 MSers (62%) with transverse myelitis (N=25, 32%) as the most common type. The clinical syndrome was chronic for 47 MSers (37%) and again transverse myelitis (N=24, 51%) was the most common type. Five-year follow up data was available for 44% of these MSers.
DISCUSSION: LOMS is rare and RRMS is the most common clinical course. Reclassification of the clinical course, not done before in any other LOMS study, with careful questioning regarding a prior neurological event reveals that SPMS is the most common type of progressive MS and PPMS may be less common than previously thought. Transverse myelitis is the most common clinical presentation.