High Presence of Sense of Smell Dysfunction Found in Patients with Multiple Sclerosis

Olfactory and gustatory dysfunction may be a useful biomarker for disease progression in individuals with multiple sclerosis (MS).

An increasing number of studies have reported olfactory dysfunction in patients with MS, ranging from 11% to 41%, and gustatory dysfunction, ranging from 4.5% to 19%.

In a longitudinal study published in PLOS ONE, investigators sought to determine the correlation between the olfactory and gustatory capacity and disease progression in patients with MS over a median time interval of 3 years.

Included in the study was a total of 20 patients with MS, of whom, 16 patients had relapsing-remitting MS (RRMS) and 4 had primary progressive MS. Of the patients with RRMS, 14 of 16 were treated with disease-modifying drugs during the testing period. Three patients received glatiramer acetate, 3 received interferon beta, 4 received dimethyl fumarate, 3 received fingolimod, and 1 patient received azathioprine.

At baseline and again at follow-up, all participants were required to complete 2 questionnaires, and also undergo an otorhinolaryngological (ORL) and neurological examination.

The investigators used the Threshold Discrimination Identification Test (TDI) for subjective olfactometry. Objective olfactometry was performed by registering olfactory evoked potentials (OEP) by EEG. For gustatory testing, the Taste Strip Test (TST) was used.

There were a total of 8 patients who did not perform the follow-up testing. Three patients were excluded due to receiving corticosteroid treatment, and 5 patients refused to perform the follow-up visit due to personal reasons. The mean number of relapses during the longitudinal study was 0,3 ± 0,5.

The results of the study showed that 50% of the longitudinal cohort showed hyposmia in the baseline TDI test, and 45% showed hyposmia in the follow-up test.

In the gustatory testing, 20% of patients showed gustatory dysfunction in the baseline measurement and in the follow-up visit. Additionally, 75% of patients with gustatory dysfunction were also hyposmic.

There was evidence of mild disease activity in the patients with a mean number of 0,3 ± 0,5 relapses over the testing period, and there was no significant change in the olfactory and gustatory capacity. Furthermore, the patients showed a good self-estimation of their olfactory capacity expressed in the visual analogue scale.

The olfactory capacity for the discrimination of odors correlated inversely with the number of relapses (r = -0.5, p ≤ 0.05). Additionally, the patients were aware of their olfactory deficit, according to the authors.

“Olfactory and gustatory dysfunction is a symptom in MS patients and may be a useful parameter to estimate disease progression in MS patients,” the authors concluded. “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.

“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 the olfactory and gustatory function. It would 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.”