After total laryngectomy surgery, nasal airflow is permanently transferred to the tracheostome, compromising the arrival of odorant molecules to the nasal cavity1,2. The decrease in olfactory (hyposmia) and gustatory (hypogeusia) perceptions of individuals undergoing this intervention is often reported in the literature3,4. Currently, it is considered that the laryngectomy may cause these changes due to the interruption that occurs in the respiratory tract, as well as by changes in the epithelial structure of the nasal mucosa and in the sensorineural feedback5,6.

These sensory changes are less frequently investigated in clinical practice, since the loss of verbal communication, pulmonary complications and the psychosocial problems are evident after this surgery, and more often rehabilitated.

The present study aimed to evaluate the smell and taste perceptions in patients submitted to total laryngectomy, compared with non-laryngectomized individuals, by means of two quantitative tests.

Most of the laryngectomized volunteers had incomplete elementary education (21, 84.0%) (p < 0.001), a more frequent history of smoking (84%) and alcohol intake (60%) (p < 0.001) and larger number of missing teeth (p < 0.05) (Table 1).

In gustatory perception tests, the mean score of correct answers among the laryngectomized patients equaled 7.2 ± 0.48 points, ranging between 1-11 points, while in the comparison group, the mean was 10.5 ± 0.7 points, ranging from 4 to 16 points. This difference was significant (F = 15.695, p < 0.001).

Considering the cutoff point for gustatory capacity adjustment8, we noticed that the laryngectomized group had significantly more frequent hypogeusia (20; 80.0%) than the comparison group (9; 36.0%) (c2 = 5. 88, p = 0.015) (Table 2).

Hypogeusia was more frequent among laryngectomized with schooling up to middle level and a history of smoking and alcohol consumption, when compared with non-laryngectomized individuals and not all of these variables were statistically significant (Table 2).

Among the sweet, salty and sour tastes, the laryngectomized group had the most frequent percentage of identification errors, while for the bitter taste it was equal for both groups (Table 3).

In the olfactory discrimination test, the laryngectomized group had a mean level of correct answers equal to 6.0 ± 0.5, points, ranging between 3-11 points, differing significantly from the comparison group, which obtained a mean level of correct answers equal to 9.1 ± 0.3 points, ranging from 6 to 11 points (F = 31.937, p < 0.001).

Similarly to that observed on the gustatory assessment, we found that hyposmia was more frequent among males with mid-level education, as well as in the presence of a history of smoking and alcohol consumption among laryngectomized subjects and all these differences were significant (Table 2).

Considering nine points as the cutoff point for olfactory capacity adaptation, according to gender and age7, we noticed that 15 (60.0%) individuals from the comparison group had normal olfactory perception for their age and gender, compared with three (12%) from the laryngectomy group. In the comparison group, 10 (40%) subjects had abnormal olfactory discrimination for age and gender - a percentage significantly lower than the 88% in the laryngectomized group (c² = 12.50; p < 0.001) (Table 2).

Table 4 shows the breakdown of this difference. Laryngectomized patients more often did not identify odors of smoke, chocolate, rose, turpentine, banana, pineapple, onions and gasoline, and all these differences were significant. Although the laryngectomized have presented lower scores in turpentine and lemon odor identification, differences in relation to the comparison group were not significant.

Comparing the groups regarding concomitant changes of olfactory and gustatory perception, we found that in the comparison group, normogeusia associated with normosmia was more frequent (10.40%); while in the group of laryngectomized patients there was a higher frequency of hypogeusia and hyposmia (18.72%). In cases where there was involvement of a single perception, hyposmia was more frequent than hypogeusia, especially among the laryngectomized patients (c² = 17.74, p < 0.001).

Males, around 60 years of age, represent a worldwide prevalence of laryngeal cancer, as previously reported in the literature9–12 - having been demonstrated in this study - which showed a significant relationship between hyposmia and males among laryngectomized patients, but not hypogeusia.

Research suggests that males have the worst olfactory performance under the hypothesis that genetics and hormonal issues can be determinant for this gender difference in sensory perception13. Other researchers point out that the reduction of smell and taste is an occurrence inherent to the physiological process of aging14. These variables must also be considered in relation to the sensory losses found in this study, although hyposmia and hypogeusia are reported in the literature as frequent changes in laryngectomized patients4,15.

The low level of education found in the laryngectomized group may be associated with socioeconomic and cultural aspects; in addition, the evaluation methods used in our study required a subjective response, taking into account reports or experiences of the subject, which should be considered in understanding the results.

The interpretation of the association between hypogeusia and hyposmia and middle-level education among the laryngectomized subjects deserves caution, because it may be related to socioeconomic status and the type of occupation these patients have.

A study carried out with a standardized test to assess the olfactory function in the Brazilian population found that socioeconomic status may influence the loss of olfactory sensation. Hazardous occupational habits and exposure to pollutants are commonly portrayed in low economic status regions, which may result in olfactory deficit16. Another issue is the prevalence of this cancer in rural Brazil12, suggesting poorer living conditions and limited access to schooling.

Cigarette smoking and alcohol consumption have been referred to as the main etiological factors for the emergence of such cancer17. These harmful practices are also associated with olfactory epithelium degeneration, destruction of taste buds, and neuronal damage, which may result in hyposmia and hipogeusia18,19. These findings should be considered, since these habits were significantly more frequent in the laryngectomized participants of this study, and were associated with hypogeusia and hyposmia, it would be interesting to control these variables in subsequent studies.

Regarding the missing teeth, this variable does not seem to have influenced the aspects studied. The similarity of the groups in this item refutes the hypothesis that such variable prevails in laryngectomized patients, although age and educational level may suggest poor oral hygiene, as well as smoking and drinking20, and the very treatment of laryngeal cancer may damage the entire oral cavity.

Other researchers3,6,19,21 corroborate the hypothesis that the olfactory and taste functions are altered in patients who underwent total laryngectomy - confirmed in our results. Considering the occurrence of hyposmia and hypogeusia significantly greater in those subjects compared to subjects not submitted to laryngectomy, such evidence is still neglected in clinical practice.

The decrease in gustatory function, characterizing hypogeusia, was strongly evident in laryngectomized patients, as well as the occurrence of changes in the distribution of flavors - this features the most important contribution of this study.

Physiologically, flavor perception occurs through taste buds diffusely located on the tongue, palate, epiglottis, pharynx and larynx22,23. Sweet and bitter tastes have the same type of intracellular activation through G-protein coupled receptors, while stimulation of salty and sour tastes acts directly on specific ion channels located in the membranes of receptor cells23–25. However, in all cases, the electrical signals produced by the methods of conversion are uploaded to the central nervous system via cranial nerves VII, IX and X - responsible for the formation of synapses in specific receptor cells23,26.

It is believed that the disruption of the complex neurological connections and sensorineural feedback caused by complete removal of the larynx may account for these gustatory changes. It is important to stress that radiation therapy, often associated with the treatment of head and neck cancer, may also result in deleterious effects to sensory organs and tissues, including the oral cavity, tongue, salivary glands, the olfactory epithelium and nerves associated with the perception of smell and taste27.

Failure to observe significant changes in the bitter taste in the study groups over the other flavors, may have some explanations. The bitter flavor is part of a body protection mechanism associated with the rejection of certain foodstuffs28.

Recent studies have indicated that the bitter taste can be detected at other sites in addition to the tongue and adjacent mouth epithelium, for receptors have been found in the gastric and intestinal mucosae24,28, limiting the absorption of bitter tasting dietary toxins that escape aversion in the mouth28.

The occurrence of hyposmia in laryngectomized individuals was confirmed in this study, with emphasis in the difficulty of perceiving certain odors. Hyposmia has been evidenced in laryngectomized patients by several authors;4,6,15 however, the mechanisms responsible for the decrease in the olfactory function of laryngectomized patients are not yet fully understood. The definitive change in nasal airflow to the tracheostome has been the most cited theory by researchers as the cause of this sensory dysfunction, given that smell depends on chemoreceptors located in the olfactory epithelium to respond to the presence of molecules in the air4,6.

Other authors have demonstrated theories related to degenerative diseases of the olfactory epithelium5,21 as well as damage caused to the complex sensorineural mechanisms due to the total laryngectomy surgery29.

The inability to detect smoke odors and other smell-related signs of danger in laryngectomized patients has been reported in studies, and this may jeopardize the safety of these individuals,3,19 similar to the results presented here, in which the identification of “warning odors” was significantly decreased.

The difficulty in the perception of certain odors can influence even food-related pleasures, resulting in weight loss and contributing to malnutrition19. Likewise, the loss of the perception of bodily odors may result in socializing difficulties3. Our findings suggest that these problems can cause feeding problems and therefore nutritional issues in this population, requiring further investigations in future studies.

Paint thinner - a common solvent in North America - smell interpretation proved unfamiliar to the participants in this study, which may be related to cultural characteristics, and therefore, without significant differences in the results presented here.

Studies detail the association between the sensory functions of smell and taste as responsible for defining the taste of food, closely related to eating habits, nutritional aspects and pleasure during eating30,31. It is important to report the significant relationship between the smell and taste functions identified here, with evidence of concomitant hypogeusia and hyposmia in more than half of the total laryngectomized group.

Nasal airflow interruption in the total laryngectomized may not only negatively affect olfactory perception but also their gustatory identification skills, as pointed out in our results. During the olfactory test, we observed facial muscle movements in laryngectomized individuals, suggesting an attempt to force nasal aeration for the consequent stimulation of nasal olfactory epithelium. While not a variable considered in our study, it is important to note that, during chewing, there is the induction of an air stream into the oral cavity by which the olfactory organ is stimulated through the nasopharynx3,23. When food approaches the mouth during the respiratory mechanism of inspiration, the olfactory epithelium is also stimulated, thus acting in conjunction with other sensory functions to determine the food flavor31–33.

The international literature4,6,21 has stressed the importance of giving greater emphasis to the treatment of these sensory functions; however, it is limited to only reporting as to the decline of these functions without qualifying with regards to the impaired distribution of tastes and odors.

This study fills this knowledge gap, proving that the perception of salty, sweet and bitter flavors are impaired in laryngectomized individuals, as well as the identification of important warning odors and other smells directly related to feeding, also reduced in this population. Thus, interventions seeking to stimulate the limitations of these sensory functions should be part of the therapeutic scope aimed at individuals submitted to total laryngectomy.

In clinical practice, it is relevant to evaluate these sensory functions and to develop rehabilitation programs for this population, given that the smell and taste alterations may trigger changes in eating habits and impact the pleasure associated with this activity and on the nutritional status of these subjects, in addition to reducing the alert in risky situations, compromising the quality of life of these individuals.

The decrease in gustatory and olfactory functions in laryngectomized individuals was evidenced in this study. In discriminating flavors, the bitter taste was not different between the groups at the expense of other flavors. In the olfactory aspect, the laryngectomized individuals performed worse in detecting warning and food-related odors. It is assumed that the decrease in olfactory function may be directly related to the decrease in the gustatory perception, considering the association between these functions for defining food taste as well as concurrent hypogeusia and hyposmia in laryngectomized individuals.