Q. Several months ago, I developed a bad taste in my mouth. I reviewed my medicines with my pharmacist, but none had that side effect. My dentist said my teeth were OK and a CT scan of my sinuses didn't find anything either. What do you think could be the cause?
--Oro Valley, Calif.
A. As is so often the case, treatment of the condition you describe depends on identifying and removing the causative factors. It certainly sounds as though you're doing your detective work. I hope this general information will help you further.
Impairment of taste and smell is a relatively common disorder, affecting approximately 2 percent of North Americans. It can be frustrating because it disrupts the ability to enjoy food, drink and aroma. But more seriously, disruption of taste and smell functions can interfere with the ability to discern spoiled food, toxic chemicals and gases or smoke.
To distinguish most flavors, the brain needs input from both the taste and smell chemical receptors, which are closely related. Except for the tongue's ability to differentiate salty, bitter, sour and sweet, true flavor is identified through the nose. Loss of the sense of taste is known as ageusia; distorted sense of taste is known as dysgeusia.
Air containing an odor must travel through the nose to reach olfactory receptors in the mucous membranes behind the bridge of the nose. These receptors identify an odor and transmit the information to the brain. Disruption of that transmission can cause absence of the sense of smell (anosmia) or diminished sense of smell (hyposmia).
Anything that hinders the journey of the electrical impulse from the odor receptors in the nose or the taste receptors on the tongue to the brain can influence the perception of taste and smell. The causes of this group of disorders are many.
Taste dysfunction can be caused by damage to any part of the sensory nerve pathway from the taste buds to the brain. That damage can be the result of other disorders or conditions (e.g., strokes, Bell's palsy, depression); trauma (e.g., head injury); heavy smoking, especially pipe; and some drugs. A dry mouth can also cause injury to taste buds.
Many drugs and toxic chemicals also can impair or distort both taste and smell by affecting the action of the receptors, as can head trauma, strokes, congenital problems and aging. Viral illness is often implicated.
The bad news is that, at present, most forms of dysgeusia are considered untreatable. You seem to have ruled out two common causes that are treatable--tooth decay and sinus infections.
The good news is that sometimes that distortion comes and goes without the cause being known. In one recent study, two-thirds of a group of patients with dysgeusia experienced spontaneous resolution of the disorder, with the average duration of 10 months.
Otherwise, treatment means detective work, followed by treating responsible systemic diseases and stopping any drugs or behavior that contributes to the problem. Can you remember doing anything unusual when the bad taste began? If the problem persists, I suggest you talk with a neurologist about possible causes.
Update on rare diseases
I'm frustrated at not being able to write about all the questions I get on rare diseases. Unfortunately, it's impossible to cover the more than 6,000 diseases that have been identified by the Office of Rare Diseases, which is part of the National Institutes of Health.
Fortunately this office, in conjunction with the National Human Genome Research Institute, has launched a new information center for the general public about these diseases. To reach them, send an e-mail to firstname.lastname@example.org, visit the Office of Rare Diseases online at http://rarediseases.info.nih.gov or call 888-205-2311.
As with accessing any other source of information, it's much better to write down all of your questions ahead of time and, if you don't understand an answer, say so and ask again.