Patient selection

The study subjects were 24 patients who underwent total or subtotal glossectomy and reconstruction with flaps ( Table 1 ). Informed consent was obtained from all patients. We excluded patients who had undergone radiotherapy and those undergoing chemotherapy at the time of the study. The patients included 21 men and three women aged 37–79 years (average age 57.8 years). All patients had undergone preoperative chemotherapy and neck dissection (bilateral, 21 cases; unilateral, four cases).

Table 2 provides details of the surgical treatment of the 24 study patients. Six patients underwent a total glossectomy, whereas 18 underwent a subtotal glossectomy. Among patients with subtotal glossectomy, operative notes indicated that >2/3 of the tongue base remained in one patient, 1/2 remained in three patients, 1/3 remained in 11 patients, and <1/4 of the tongue base remained in three patients. In addition, 11 patients were able to see their remaining tongue from the mouth. Twenty-two patients underwent reconstruction by free rectus abdominis musculocutaneous flap, one by free anterior lateral thigh perforator fasciocutaneous flap, and one by pectoralis major myocutaneous flap. The timing of assessment ranged between 2 months and 158 months, with an average of 30.5 months after operation.

Interview on taste perception

Subjective symptoms were evaluated by medical interview alone. In particular, it was not considered to be a problem if the patient did not recognize that they had a taste disorder, even if their taste threshold was low. Patients were interviewed about diet, subjective symptoms of taste, and taste changes after surgery. Diet was classified into the following four grades : grade 1 was defined as good, i.e., a diet cooked and eaten in a regular manner, or a diet identical to that before surgery; grade 2 was acceptable, i.e., a softer diet consisting of rice gruel, stewed vegetables, and viscous foods for added thickness; grade 3 was poor, consisting of liquids or a diet prepared by blender and not normal in appearance; grade 4 was defined as an inability to take adequate food by mouth so that tubal feeding was required. Grades 1 and 2 resemble a normal diet, in which eating is a pleasure as well as nutritional support. The immediate sensory impression of the food is dominated by taste, smell, vision, and oral haptic perception, and these modalities interact with each other. Odorants may enhance or suppress taste and vice versa. Food texture affects taste and smell and vice versa. We therefore believe that diet is one of the important factors in taste perception after glossectomy.

Taste test protocol

A taste test by filter paper disc method, one of the few objective estimates of taste besides electrogustometry, was used to evaluate the taste threshold. This method is carried out using the four basic tastes divided into five concentration grades: 0.3%, 2.5%, 10%, 20%, and 80% sucrose (sweet); 0.3%, 1.25%, 5%, 10%, and 20% NaCl (salty); 0.02%, 0.2%, 2%, 4%, and 8% tartaric acid (sour); and 0.001%, 0.02%, 0.1%, 0.5%, and 4% quinine (bitter). Each solution has no smell. Differential thresholds were determined by testing increasing concentrations followed by rinsing with water, and there was an interval of more than 30 s before proceeding to the next taste. In accordance with the manufacturer’s instructions and the original study, the bitter taste was tested last, but the others were randomized so that the subjects would not anticipate the next taste. To prevent aspiration, we used a fine cotton swab instead of the original filter paper disc. Soaked cotton swabs were placed on the posterior wall of the oropharynx and the remaining tongue, if it was visible. The lowest concentration was designated as the threshold score for each taste. If grade 5, the highest concentration, was not identified, we assigned a score of 6. The same test was performed on the tongue of 15 healthy adults (nine male and six female; mean age 34.0 ± 8.1 years) as a control.

The study design and protocols were approved by the institutional ethics committee.