Olfactory function and cognition in relapsing–remitting and secondary-progressive multiple sclerosis

Background: Both cognition and olfaction are impaired in multiple sclerosis (MS). However, little is known about the relationship between smell identification ability and measures of cognitive function in this disease. Objective: To assess olfactory function in MS and to evaluate its relationship with cognitive and physical disability. Methods: Fifty-five MS patients and 20 healthy controls (HCs) were tested. The University of Pennsylvania smell identification test (UPSIT) was administered to assess olfactory function. Cognitive function was tested using the symbol digit modalities test (SDMT), California verbal learning test-II (CVLT II), brief visuospatial memory test (BVMT), paced auditory serial addition test (PASAT), and controlled oral word association test (COWAT). Fatigue and depressive symptoms were evaluated using the Modified Fatigue Impact Scale and the Beck Depression Inventory II, respectively. Results: MS patients had lower UPSIT scores than those of the HCs (28.76 ± 5.48 vs 31.7 ± 2.18, p = 0.02), with secondary-progressive and cognitively impaired MS patients showing the greatest impairment. Scores on the SDMT, CVLTII, BVMT and COWAT were related to the olfactory test scores. Conclusion: We confirm that olfactory function is impaired in MS, particularly in progressive phenotypes, and show, for the first time, that such dysfunction is related to a broad range of cognitive measures. Our data suggest that olfactory dysfunction might be considered as an indirect measure of MS severity. Longitudinal studies are needed to confirm this possibility.