Smell Disorders in Multiple Sclerosis
Smell disorders (aka olfactory dysfunction) affect a significant number of people who have multiple sclerosis. A new study explains that olfactory dysfunction impacts the quality of life of MS patients and that a better understanding of this challenge could result in improved disease management.
A team at the Pennsylvania State University-Milton S. Hershey Medical Center recently reviewed the phenomenon of olfactory dysfunction among individuals with multiple sclerosis, which may occur in 20 to 45 percent of patients. They noted that smell disorders correspond with disability in MS and that severity may change with relapses.
Olfactory dysfunction includes a loss of the ability to smell or a change in how a person perceives different odors. Complete inability to smell is called anosmia while a reduction in the sense of smell is called hyposmia.
Problems with the sense of smell can be problematic on several levels, not least of which is its impact on the sense of taste. Inability to detect odors also can be dangerous if individuals cannot identify harmful substances such as gases or smoke.
Elizabeth B. Lucassen, MD, who headed the review of 40 studies, and her team explained that a better understanding of smell disorders in people with MS “may elucidate its relationship to disease activity, stage of disease, neurodegeneration, and correlations with other MS co-morbidities.” Among the things experts still do not fully understand are the changes in the ability to smell that occur during the course of the disease, how olfactory function correlates with cognition and other MS issues, and the correlation between olfactory function, MS activity, and relapses.
Lucassen explained that measurement of olfactory function in multiple sclerosis could help clinicians identify when patients have secondary progressive disease and are no longer likely to benefit from taking disease-modifying therapy. It’s also possible that smell disorders are an indication of more widespread brain dysfunction in people who have multiple sclerosis.
Other smell disorder studies in multiple sclerosis
In a recent related study, a team in Turkey explored the association between olfactory bulb and olfactory sulcus depth and disease duration and attack frequency. The olfactory bulb is a structure in the forebrain that receives neural input concerning odors and thus is involved in the sense of smell, while the olfactory sulcus is a deep groove on the frontal lobe, the depth of which relates to olfactory function.
The olfactory bulb and olfactory sulcus depth were evaluated in 25 people with multiple sclerosis and 30 healthy individuals. Both features were significantly lower (atrophied) in the individuals with multiple sclerosis than in the healthy controls. These findings correlated with disease duration and attack frequency.
In a 2013 study, the olfactory function as well as medical information were evaluated in 50 individuals with remitting or secondary progressive MS. Forty percent of the patients had hyposmia, and the authors noted that the ability to identify odors, which declines over time, is associated with the level of disability.
Smell disorders and changes in how one perceives odors progresses over time in many people who have multiple sclerosis. No treatments are currently available for this challenge, which is the result of demyelination and loss of axons in olfactory tissue.
Lucassen EB et al. Olfactory dysfunction in multiple sclerosis: a scoping review of the literature. Multiple Sclerosis and Related Disorders 2016; DOI:10.1016/j.msard.2015.12.002
Tanik N et al. Olfactory bulb and olfactory sulcus depths are associated with disease duration and attack frequency in multiple sclerosis patients. Journal of the Neurological Sciences 2015 Nov 15; 358(1-2): 304-7
Rolet A et al. Olfactory dysfunction in multiple sclerosis: evidence of a decrease in different aspects of olfactory function. European Neurology 2013; 69(3): 166-70