Credit: Thinkstock The senses of smell and taste are closely related. Working together they can both alert us to dangers and enhance our enjoyment or dislike of certain foods. Our tongues are covered in thousands of little bumps called taste buds. These taste buds contain receptors that allow us to perceive five elements of taste: sweet, sour, salty, bitter, and savory.
A reduced ability to taste is called hypogeusia. A distortion in taste is called dysgeusia or parageusia. The complete lack of the sense of taste is called ageusia.
There are many things that can alter one’s ability to taste, such as common viral infections, smoking, or certain medications. People with multiple sclerosis (MS) undergoing intravenous steroid treatment for relapse frequently report a temporary “metallic” taste in the mouth. But that’s not the only way that MS might affect taste.
A problem with taste in MS is thought to be rare; but when it does happen, it can seriously impact one’s quality of life. A 2016 study published in the _Journal of Neurology_reported that taste deficits may be more common in people with MS than previously thought and are associated with MS-related lesions in specific parts of the brain.
The study aimed to determine how common and severe problems with taste may be in MS. Then they tried to correlate specific types of taste deficiencies with the location of brain lesions. Researchers recruited 73 people with MS and 73 healthy individuals to participate in the study.
Each participant took part in a 96-trial taste test that measured perceptions of sweet (sucrose, a type of sugar), sour (citric acid, commonly found in citrus fruits such as lemons), bitter (caffeine, found in tea and coffee), and salty (sodium chloride, found in table salt). Each ingredient was tested six times, with varying intensities, on four regions of the tongue connected to cranial nerves VII and IX. Participants were also tested with Gd-enhanced MRI scans.
The percentage of people with MS who had significantly more trouble identifying specific tastes, with scores falling below the 5th percentile of the control group, were 15.07 percent for caffeine (bitter), 21.9 percent for citric acid (sour), 24.66 percent for sucrose (sweet), and 31.5 percent for sodium chloride (salty). That’s one out of four people with MS having difficulty tasting sweet and almost one-third with difficulty tasting salty things.
People who had more trouble identifying tastes also had larger volume of lesions in specific areas of the brain, particularly the frontal and temporal lobes. In general, women were better at identifying flavors than men in both groups.
An altered sense of taste is not one of the symptoms that is typically included on questionnaires regarding MS. But it has been reported to be a presenting symptom in some MS case studies. For example, a 49-year-old woman, who experienced sudden dizziness, double vision, and slurred speech, had developed hypogeusia days before her neurological attack. Doctors found a single, small lesion in her lower midbrain. She was treated with high-dose steroids and eventually recovered from her attack. Almost two years later, she had a relapse with another brainstem lesion and was finally diagnosed with clinically definite MS.
If you suddenly notice that food just doesn’t taste the same or if you’ve lost your appetite and are losing weight, discuss this with your neurologist. It could be your MS.
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Doty RL, Tourbier IA, Pham DL, et al. Taste dysfunction in multiple sclerosis. J Neurol. 2016 Jan 25. [Epub ahead of print]
Hashimoto T, Doden T, Ono Y, Uematsu T. Bilateral hypogeusia caused by a small lesion in the lower midbrain tegmentum. BMJ Case Reports. 2012; 2012: bcr2012006837. Published online 2012 Sep 11. doi: 10.1136/bcr-2012-006837