Poorer Sense of Smell Can be Evident in the Early Stages of MS

Those with multiple sclerosis have been known to have a worse sense of smell than others, and a small Turkish study, “Olfactory dysfunction in multiple sclerosis,” finds that these problems could be starting at the earlier stages of disease development.

The work supports previously conducted studies that also note these olfactory problems in MS patients. It argues that longer disease duration and more relapses are associated with overall greater difficulties which researchers said reflects, “More extensive involvement of the central nervous system and olfactory network in MS disease.”

Some scientists, on the other hand, disagree, as lesions are rarely evident in the olfactory nerve. The weakened ability to smell odors or the alterations of the way smells are known to be non-motor symptoms of MS.

The olfactory nerve lacks myelin, which is usually destroyed in those with MS, therefore researchers have thought that olfaction was spared damage, though new evidence shows there is greater involvement of the olfactory network in MS than previously assumed.

Olfaction has been shown to be damaged in the early stages of neurodegenerative diseases like Parkinson’s or Alzheimer’s disease. Studies suggest that olfactory impairment could be used as a bio-marker for diagnosing neurodegeneration.

Data from clinical studies addressing smell function in MS indicate a 20 to 40 percent olfactory impairment in MS, mainly in patients with relapsing-remitting MS but also in those with primary progressive MS. Some studies, on the other hand, report no olfactory problems associated with the disease.

Researchers in Turkey evaluated the link between olfactory dysfunction and MS duration progression along with patients’ cognition. Using MS patients from an MS clinic in Istanbul, the team analyzed a total of 31 adult patients with a minimum follow-up period of five years and 24 healthy controls.

Everyday items were used in the smell identification test such as peanut butter, soap, chocolate, coffee, cinnamon, mothballs and baby powder. The results revealed that MS patients, especially those with longer disease duration and frequent relapses, performed worse than controls on the olfactory test. Better cognitive status was also linked to superior olfactory test scores.

Investigators wrote that, “olfactory testing could be a useful surrogate for cognitive dysfunction in MS patients, apart from their physical disability status.”

While no correlation was directly found between patients’ level of disability and their olfactory perceptions, a larger study may be needed in order to see these results. The researchers did conclude that the study, “supports the presence of a possible relationship between MS and olfactory system involvement, and the correlation of cognitive impairment with olfactory dysfunction, even in the early stages of the disease in young and less physically disabled patients.”