A study found that patients with relapse-remitting multiple sclerosis (RRMS) are nearly twice as likely than controls to experience olfactory dysfunction. The researchers also identified a correlation between olfactory dysfunction and fatigue in patients with RRMS treated with dimethyl fumarate or fingolimod.
Thirty controls and 30 patients with RRMS were compared. Patients with RRMS were treated with either injectable (interferon β or glatiramer acetate, n=18) or oral disease-modifying therapies (dimethyl fumarate or fingolimod, n=12). The Sniffin’ Sticks Identification Test (SSIT) was used to determine hyposmia, which was defined as a SSIT olfactory test score ≤6 points. Data collection included number of previous relapses, disability in Expanded Disability Status Scale (EDSS), recent MRI scan of the brain, thalamic volume, and third ventricle width. Two years after the olfactory assessment, patients were evaluated for cognition per the Symbol Digit Modalities Test (SDMT) and fatigue per the Fatigue Scale for Motor and Cognitive Functions (FSMC).
Patients with RRMS were more likely than controls to have hyposmia (66.7% vs. 36.7%; odds ratio, 1.82; 95% confidence interval, 1.10-3.67; P=0.02). The number of previous relapses; new brain MRI lesions; EDSS, SDMT, and FSMC scores; thalamic volume; and third ventricle width were not associated with SSIT score (P>0.05). Olfactory dysfunction was associated with the FSMC cognitive subscale among patients receiving oral drugs (P=0.006).