Olfactory dysfunction can frequently be measured in multiple sclerosis patients, according to research published in Multiple Sclerosis and Related Disorders.
While previous studies have reported olfactory dysfunction in multiple sclerosis (MS), results have been inconsistent. To synthesize and interpret existing knowledge about olfactory dysfunction in MS and identify current gaps in knowledge, Elisabeth Lucassen, MD, from the Departments of Neurology at Pennsylvania State University-Milton S. Hershey Medical Center, and colleagues conducted a review of 25 clinical studies examining olfactory dysfunction in patients with MS.
Among them, 23 studies measured olfactory dysfunction in MS patients, 10 evaluated MRI correlates of olfactory dysfunction, and 5 evaluated neurophysiology correlates of olfactory dysfunction. Thirteen reviews or commentaries and 2 case studies were also included.
CLINICAL CHART: Multiple Sclerosis Treatments
“The majority of the studies identified some degree of olfactory dysfunction in MS patients, and various aspects and correlations with olfactory impairment were observed,” the authors wrote, showing that the overall weight of the existing knowledge on the subject suggests that olfactory dysfunction may occur in MS, with both threshold and identification deficits observed. Although the researchers found variability in the reported frequency of olfactory dysfunction, the more robust studies suggest that the prevalence is significant, ranging from 20% to 45% in the MS population.
While their review indicated that olfactory dysfunction may be frequently measured in MS patients, the researchers identified many questions that require further study. Despite evidence of a high prevalence of olfactory dysfunction, its mechanisms are unknown and the clinical relevance of the association has not been well explored. Correlations between olfactory dysfunction and cognitive dysfunction as well as depression and anxiety have also been observed, but these findings remain poorly developed and require further investigation.
Future studies to understand the dynamic changes in olfactory function during the course of MS are also warranted, as well as studies that correlate olfactory function with relapses and disease activity.
Lucassen EB, Turel A, Knehans A, Huang X, Eslinger P. Olfactory dysfunction in Multiple Sclerosis: A scoping review of the literature. Mult Scler Relat Disord. 2015; doi:10.1016/j.msard.2015.12.002.