Lost taste perception associated with more MS brain lesions.
Many patients with multiple sclerosis (MS) lose the ability to distinguish different tastes — a signal associated with MS-related lesions in the brain, researchers reported.
Taste identification tests revealed that scores were significantly lower in MS patients than controls for sweet (P=0.0002), sour (P=0.0001), bitter (P=0.0372), and salty (P=0.0004), Richard Doty, PhD, of the University of Pennsylvania, and colleagues reported online in the Journal of Neurology.
On magnetic resonance imaging (MRI), the taste test scores were correlated with lesion volumes in the frontal and temporal lobes, Doty and colleagues reported.
“The present study clearly demonstrates that MS is commonly associated with decrements in the ability to identify all four classic taste qualities within both anterior and posterior regions of the tongue,” they wrote. “Female MS patients, like women in general, identified tastants more accurately and rated their perception as more intense than did male MS patients.”
“Our study demonstrates that lesion volumes within large sectors of the frontal and temporal lobes are correlated with functional measures of taste,” they added.
The influence of MS on taste may involve higher brain structures, the researchers said, since the study showed that the number of brain structures directly associated with taste function had no or few MS-related lesions. This may also explain why most MS patients have normal taste function.
“Lesions made up <2% of the volume of the large brain regions with the most lesion activity, suggesting that only a minority of such lesions impact neural pathways related to taste function,” they said.
Still, Doty noted in an interview that a number of MS patients suffer from malnutrition.
“Although more research needs to be done, our study, along with others, suggests that a significant number of patients with MS experience losses of both taste and smell — losses which can significantly impact eating, enjoyment of food, and nutrition,” he told MedPage Today.
In the study, 73 patients with well-documented MS and 73 healthy controls matched for age, sex, ethnicity, and education were enrolled. All participants underwent a 96-trial test of sweet (sucrose), sour (citric acid), bitter (caffeine), and salty (NaCl) taste perception to the left and right anterior and posterior tongue regions. A total of 63 MS patients also underwent MRI of the brain in 52 regions.
The study showed that the prevalence rate for taste dysfunction in MS patients was 15% to 32% relative to controls, said the investigators. This is about half of that for optic neuritis, a diagnostic hallmark in MS, they pointed out.
“This suggests that altered taste function, albeit modest in magnitude and less noticeable than changes in vision, is a relatively common feature of MS,” they wrote.
A high percentage of MS patients consistently fell below the 5th percentile when compared to controls in identifying bitter (15.07%), sour (21.9%), sweet (24.66%), and salty (31.50%), the researchers reported. These taste deficits were present in both anterior and posterior tongue regions, and female MS patients were more accurate than their male counterparts in identifying tastes and rated them as more intense:
- Sucrose: 5.77 (0.15) versus 4.90 (0.23), P=0.002
- Citric acid: 5.06 (0.14) versus 4.10 (0.23), P<0.0001
- Caffeine: 5.33 (0.15) versus 4.03 (0.24), P<0.0001
- Sodium chloride: 5.29 (0.15) versus 4.64 (0.24), P=0.023
Results also showed that taste scores were inversely correlated with lesion volumes in the temporal, medial frontal, and superior frontal lobes, and with the number of lesions in the left and right superior frontal lobes, right anterior cingulate gyrus, and left parietal operculum. No taste deficits relative to lesions within the pons, brainstem, or elsewhere were observed.
Clinicians rarely measure smell or taste in MS patients and many patients don’t know until they are tested that their ability to taste has dulled, Doty said.
“Certainly, awareness on the part of both the patient and physician of chemosensory deficits can lead to better nutritional counselling that can improve general health,” he said, adding that larger studies are “needed to explore factors that contribute to chemosensory disturbances and pharmacological approaches that may mitigate them.”
Alexander Rae-Grant, MD, of the Cleveland Clinic Mellen Center, who wasn’t involved in the study, agreed that the findings need to be confirmed in an independent cohort.
“We know that specific lesions in the brainstem could affect taste, but symptoms referable to a lesion in these areas is uncommon in MS,” Rae-Grant told MedPage Today. “We know, however, that patients with Parkinson’s or Alzheimer’s disease may have reduction in smell function, so it’s not impossible that there will be some smell and taste disorders in the MS population.”
Like Doty, Rae-Grant acknowledged that physicians usually don’t ask about problems with taste or smell when evaluating MS patients: “One thing we could watch for is if a patient with MS began losing weight, taste perception may be part of the issue.”
This research was supported by the U.S. National Institutes of Health.
The study authors reported no conflicts of interest.
