[Global and Spatial Gustatory Function after Proven Unilateral Transsection of the Chorda Tympani].

Background: A transection of the chorda tympani results in loss of spatial gustatory function on the ipsilateral tongue. Most patients do not notice anymore this alteration. The cause is unclear. Do adjacent gustatory areas become more sensitive or is the gustatory perception rather independent of the size of stimulated area?

Methods: 51 patients with proven unilateral transection of the chorda tympani and 51 healthy subjects were tested for gustatory recognition thresholds. The methods used were the "three-drops-choice-technique" by Henkin to evaluate the whole mouth taste (global taste examination) and the "spatial taste test" to evaluate the local gustatory function on 4 areas of the tongue. The taste solutions were sweet, sour, salty and bitter with increasing concentrations.

Results: The global gustatory function of the patients and of the control group did not differ in either the 4 taste qualities but the composite score was increased within the group of patients. Most patients did not realize that. The spatial taste examination showed reduction of taste perception on 3 of the 4 gustatory areas of the tongue in the patients. The decreased gustatory function on the area of the transected chorda remained unchanged over time. The taste attenuation on the ipsilateral back area and the contralateral front area improved over time.

Conclusion: Transection of chorda tympani also leads to an attenuation of spatial gustatory function in adjacent areas. Therefore, adjacent areas cannot be taken as reference. Instead, taste function has to be compared to the results of healthy probands.