Gustometry (synonyms: taste test, taste test, taste test) is a diagnostic procedure used in ear, nose, and throat medicine to test the sense of taste, for example, to detect nerve lesions (nerve damage). Gustometry is performed with the application of various taste substances at several locations on the tongue, in order to be able to ensure an accurate evaluation of the various sensory nerve branches of the facial nerve and the glossopharyngeal nerve in the tongue area (the sensation of taste in humans arises, among other things, from the function of two nerves, some of which nerve fibers are located in the tongue). In the application of gustometry there are different variants with different ways of execution. Gustometry can be used in diagnostics as a subjective or objective method. Moreover, there are different methods to cause irritation of the taste receptors of the tongue.
Indications (areas of application)
- Gustometry can be performed for any subjective impairment of the sense of taste to determine whether a nerve lesion is involved and where it is located.
- In addition to these peripheral lesions (damage located outside the brain), there may also be a disorder caused by damage to the brain structure in Parkinson’s disease or Alzheimer’s disease, so that the taste disorder (dysgeusia) can be considered an early symptom of the diseases.
- Another field of application of gustometry is the side effect testing of drugs, since many drugs can cause an often spontaneous reduction in taste sensation.
- In addition, many metabolic diseases such as diabetes mellitus type 1 and 2 can also cause a reduced taste sensation, so that a detected hypogeusia (reduction in taste sensitivity) can serve as an indicator (indicator) for further diagnostic procedures.
The procedure
The principle of gustometry is functional testing of the sense of taste by means of stimulation of the sensitive nerve endings, which are caused, for example, by the application of flavors to the surface of the tongue. A distinction is made in gustometry between three supergroups:
- Classical gustometry or chemogustometry: in this method, taste-intensive substances are applied to cotton swabs and placed on specific areas of the patient’s tongue. The sense of taste is tested using samples of the four taste qualities: sweet, sour, bitter and salty. A 10 percent glucose solution (the percentage reflects the amount of glucose in the test fluid), a 7.5 and 15 percent NaCl (saline) solution, as well as 5- and 10-percent citric acid and 1- and 5-percent quinine (bitter) are used for testing. However, the results are not considered very reproducible because of the possibility of simulation or aggravation (arbitrary exaggerated emphasis on the symptoms of the disease, which is due to increased self-observation). Because of the possible influence, the procedure is called subjective gustometry.
- From this method can be distinguished electrogustometry: here, the taste receptors of the tongue surface are stimulated by a constant current and the strength is determined, at which the stimulus via the taste receptors are perceived by the patient. The value determined in this way is called the taste threshold and represents the lowest stimulation of the taste receptors that leads to the sensation of a taste. Although this procedure is performed without the use of taste samples, it is still not an objective procedure.
- The only objective taste testing is done by measuring gustatory evoked potentials in the EEG (by stimulating a nerve located in the tongue, a change in activity in the brain can be measured).
About the procedure of gustometry:
- The patient is asked to stick out his tongue before the actual testing of the sense of taste. Following this, the brushing of the respective tongue area with the cotton swab is performed.
- After each test of a taste quality, the mouth must be rinsed to avoid getting false results.
- The implementation of electrogustometry is, of course, as described with the stimulation of the receptors in the tongue surface via electric shocks.
- The assessment of the sense of taste must always be done by side comparison. In addition to the patient’s indication of when he notices an irritation of the taste receptors, he must indicate which taste quality it is.
- Furthermore, it is crucial for the performance of the examination that the patient does not take the tongue back in the mouth during the examination, since this could experience the taste sensation also the healthy side in the case of a unilateral nerve lesion.
Although a reduction in the sensitivity to taste can be interpreted as an early symptom of many diseases, in the vast majority of cases it is based on an age-related change. The deterioration is a result of the change in the surface structure of the tongue that accompanies age. Smoking or excessive alcohol consumption can also worsen the sense of taste. Since hypogeusia may be present as an early symptom of a serious underlying disease, the results of gustometry should not be neglected. Thus, what is critical for the patient is not to identify the taste disorder but rather to identify the cause of the disorder.
