People with the autoimmune disease myasthenia gravis tend to develop an unusual symptom: they lose the sense of smell. This may not sound so bad when the septic tank overflows, but the condition, called anosmia, can have serious consequences. How food tastes is closely tied to how it smells, meaning people with anosmia don’t get the full taste of food; this lack of a psychological reward for eating can result in poor appetite and malnourishment. Moreover, the nose can act as a sentry for the body, with spoiled food and harmful microbes having foul odors that stimulate an immune response.
Researchers gave a standard scent identification test to patients with myasthenia gravis, patients with a similar disorder called polmyositis, and healthy subjects. These subjects were also given a picture recognition test, in order to distinguish problems identifying smells in particular from more general recognition problems—the researchers wanted to rule out overall cognitive impairment, though that’s not generally a symptom of myasthenia gravis.
What they found was that people with myasthenia gravis have significantly reduced ability to smell things—and this held regardless of severity, duration, or even having or not having a history of smoking. In severe cases, myasthenia gravis is treated by removal of the thymus gland, which develops a tumor in about one in every seven cases of the disease, and this surgery has no effect on the olfactory dysfunction.
Other symptoms of the condition, in which nerves and muscles don’t communicate properly, causing fatigue and weakness, include drooping eyelids, double vision, problems chewing or swallowing, difficulty with speech or facial expressions, weakness in your arms, and neck muscle problems that make it difficult to hold your head up. Myasthenia gravis is an autoimmune disease, in which the body attacks receptor sites for the neurotransmitters that carry messages from the brain to the muscles.
One of the most common first-line treatments focuses on increasing the number of those neurotransmitters, so that even with some of the receptors gone, the signal can still get through. Another option often used is suppressing the immune system, protecting the receptor sites. Recent research has looked at the possibility of modifying only the immune response to those sites, rather than throughout the body, reducing side effects.