Sense of Smell Is Impaired in Half of Multiple Sclerosis Patients in Study

Many multiple sclerosis (MS) patients have a reduced sense of smell, and the more relapses they have, the worse the problem, according to a study suggesting that smell may be a marker for the disease’s progression.

Findings also suggested a connection between reduced sense of taste and MS progression.

The study, “Longitudinal Testing of Olfactory and Gustatory Function in Patients with Multiple Sclerosis,” was published in the journal PLOS ONE.

Researchers followed 20 patients for three years. Their main goal was to determine whether loss of smell is connected with disease progression.

Roughly half the patients had reduced sense of smell, or hyposmia, at the beginning of the test period. They were aware of their olfactory impairment.

Two tests were used to assess smell. One was the Threshold Discrimination Identification test, or TDI, which covers a person’s ability to detect smells and tell the difference between smells. The other was the Olfactory Evoked Potential test, or OEP. It uses an electroencephalogram, which measures electrical pulses originating in the brain, to measures delays in the brain’s reaction to smells.

The patients were also tested for their sense of taste, or gustatory functioning, using the Taste Strip Test (TST).

Researchers use the smell tests to group patients in three categories: those with anosmia, or total loss of smell; hyposmia, or reduced sense of smell; and normosmia, or normal smell.

Follow-up testing led to 19 of the 20 patients being classified as hyposmic. Nine, or 45% of the patients, were classified as hyposmic on the basis of their TDI results, and 10 or 50% on the basis of their OEP results. None of the patients was classified as anosmic.

Twenty percent of patients showed taste dysfunction in the follow-up.

The higher the relapses that patients had during the three years, the lower their ability to distinguish odors, the study found.

“The results from this study underline the persistence of olfactory and gustatory dysfunction in MS patients,” the authors wrote. “This suggests that the olfactory capacity for the discrimination of smells might be a marker for disease progression in MS patients As the discrimination of odors is processed in higher central regions of the central nervous system (CNS), the results suggest that olfactory dysfunction could be due to CNS damage.

The authors also noted:

“This study is possibly the first investigation into olfactory and gustatory function in more than 5 MS patients longitudinally. The patients in our study showed mild disease activity and no relevant changes in their olfactory and gustatory function. It would be interesting to perform olfactory and gustatory testing in patients with highly active MS to investigate possible increased olfactory and gustatory disturbances and the correlation to MRI activity.”