Olfactory dysfunction in multiple sclerosis: association with secondary progression

Objective: The Brief Smell Identification Test (B-SIT) was used to explore odour identification capacities in multiple sclerosis (MS). Methods: In total, 153 consecutive patients with MS and 165 healthy controls (HC) participated in the study. All participants were asked to answer the B-SIT and the Hospital Anxiety and Depression Scale (HADS). The Expanded Disability Status Scale (EDSS), the Multiple Sclerosis Severity Scale (MSSS), and the Mini-Mental State Examination (MMSE) were used for patients' clinical and cognitive characterization. Results: Patients with MS (11.1%) were more impaired on the B-SIT than HC participants (3%). The frequency of impairment was higher for patients with secondary progressive (SPMS; 11/16, 68.8%) than relapsing-remitting (RRMS; 4/121, 3.3%) or primary progressive (2/16, 12.5%) courses. A threshold score of <= 8 on the B-SIT provided a sensitivity of 69% and a specificity of 97% in the identification of SPMS among patients with relapsing onset. The association between SPMS and impaired B-SIT remained statistically significant after adjusting for demographic (i.e. age and education), clinical (i.e. disease duration, EDSS, and MSSS), psychopathological (i. e. HADS anxiety and depression scores), and cognitive (i. e. MMSE) variables. Conclusions: A brief odour identification measure provided a good discrimination between SPMS and RRMS courses. A systematic assessment of olfactory functions may contribute to the development of clinical markers of SPMS.