MS Disease Progression Could Be Monitored With Smell Test: Study

Disconnect seen between patients' self-reported ability, performance results

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Evaluating a person’s sense of smell may help monitor disease progression in people with multiple sclerosis (MS), according to a recent study.

Almost a third of MS patients studied showed signs of smell loss in clinical evaluations and the degree of impairment correlated with clinical measures of disease, such as disability, MS duration, and cognitive performance.

“Smell appears to be a disease marker in MS and [patient-reported outcome measures] and olfactory ability tests may be introduced into core outcome sets used in clinical trials in MS,” the researchers wrote.

The study, “Smell as a Disease Marker in Multiple Sclerosis,” was published in the Journal of Clinical Medicine.

An increasing number of studies show MS patients have a loss of sense of smell that can emerge early in the disease, but reports on the prevalence of symptoms vary significantly.

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Smell Test Might Help Predict if MS Treatments Are Working

Smell tests could be a way to monitor MS progression and the effectiveness of treatments, it’s been suggested. A small study found that measures of olfactory threshold, or how sensitive a person’s nose is, could predict relapse risk in MS patients.

Researchers in Greece investigated whether there is a correlation between hyposmia (loss of sense of smell) and various clinical characteristics in MS patients.

The analysis included 115 MS patients with a mean age of 38.7 who were recruited during clinical practice at a multiple sclerosis center in Greece. A total of 56 healthy participants matched in age and sex served as a control group.

Most patients had relapsing-remitting MS (72.2%) and the remaining had a primary progressive (13.9%) or secondary progressive (13.9%) disease course.

Patients had been living with the disease for an average of 10 years and had a mean score on the expanded disability status scale (EDSS) of 3.7, reflecting moderate to significant disability, but retaining the ability to walk.

In self-reports, most MS patients (93.9%) and the control group members (92.7%) reported minimal or no olfactory symptoms. Similarly, most in both groups reported minimal or no taste disorders or nasal discharge. More patients (96.6%) reported minimal or no nasal or breathing difficulties compared with controls (80.4%).

Self-reported nasal obstruction symptoms and olfaction-associated quality of life did not significantly differ between patients and controls, but patients reported significantly worse nasal symptom-related quality of life. That difference was largely driven by fatigue and sleep disorder, analyses found.

A “Sniffin’ Sticks” test was used to clinically evaluate different components of smell. This assessment uses three visually identical sticks, each containing odorants at various concentrations, to evaluate a person’s ability to detect and distinguish odors.

Three measurements were obtained: odor threshold, or the lowest concentration of a single odor that can be perceived; odor discrimination, the ability to distinguish between different smells; and odor identification, which involves sniffing an odor and accurately identifying what it smells like. A person’s overall olfactory impairment was determined on a scale of 0 to 48, based on the performance on the three tests. Patients with scores of 30.75 or above were considered to have normal smell.

A total of 30.8% of patients had a score below 30.75, indicating hyposmia. Patients had significantly lower scores in the odor discrimination domain and overall olfactory impairment compared with healthy controls.

The finding notably contrasted with patients’ self-reports where most said they didn’t have an impairment.

“The discrepancies between patient-reported olfactory ability and psychophysical results have been extensively described, and are even more important for [people with MS] since this is a multifaceted condition possibly affecting the person’s cognition, mood, and typically inducing fatigue,” the researchers wrote. “These factors further complicate the valid evaluation of olfaction and render necessary the psychophysical testing [e.g. Sniffin Sticks test].”

Results also showed some measures of smell impairment correlated with clinical measures of MS. In particular, worse odor discrimination and greater overall olfactory impairment were correlated with a higher EDSS score, indicating greater disability, and a longer disease duration.

A better information processing speed was associated with greater odor threshold, odor discrimination, and less overall olfactory impairment. Fatigue was associated with a lower odor threshold and overall olfactory impairment predicted worse visuospatial memory.

The findings indicate “olfactory dysfunction might be a useful and easily obtainable parameter to monitor patients with regard to inflammation and neurodegeneration in MS,” the researchers wrote, adding that “olfactory function is changing in MS in accordance with disease progression and can be used as a disease marker.”

“The addition of MRI measurements and the infection history in the overall patient evaluation is expected to be of increased value for future studies,” they concluded.

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