Prognostic value of odor identification impairment in multiple sclerosis: 10-Years follow-up

•Impaired olfaction has long-term prognostic value in progressive MS.•Impaired olfaction is associated with disease severity and shorter survival time.•A B-SIT measure can be a marker of neurodegeneration in progressive MS. Olfactory dysfunction has been linked to clinical severity variables in multiple MS populations. Though, its prognostic value is still unknown. The aim of this study was to explore the long-term outcome associated with Brief-Smell Identification Test (B-SIT) performance in a cohort of MS patients. A retrospective review of the clinical records was conducted in 149 patients who participated in a previous study, with a median follow-up of 121 months. Demographic and clinical data regarding the last clinical appointment with EDSS measurement were collected. Multiple Sclerosis Severity Scale (MSSS) and Age-Related Multiple Sclerosis Severity (ARMSS) scores were calculated. Date of the last clinical contact or death was recorded. Among MS patients with progressive clinical course (n = 33), those with impaired B-SIT at baseline had greater change per month during follow-up (as measured by increases in MSSS and ARMSS scores) and a higher hazard of death. No significant associations were found among patients with relapsing and remitting MS (n = 116). The study results demonstrate that odor identification impairment has prognostic value in progressive MS, suggesting that a brief odor identification measure can be a marker of neurodegeneration in progressive MS.