EGM-thresholds
A statistically significance difference was observed between the values
prior to starting the therapy and one week after (p=0.02, Cohen’s
d-Test=0.35). At that time, patients had complaints of hypogeusia (n=6),
allogeusia (n=1) and dysgeusia (n=1). When the third measurements were
made, hypogeusia was reported by every patient, while 3 patients also
complained of dysgeusia. A further deterioration in EGM-threshold values
was observed in the subsequent measurements, which included the
follow-up measurements following RCT. Table 1 shows the mean
EGM-thresholds of the evaluated patients.
Structural alterations associated with the fungiform papillae
The fPap shape and vascularisation of the tip of the tongue exhibited a
significant deterioration when therapy was being delivered based on the
classification criteria of Negoro. It appeared that the fPap parameters
(form and vascularisation) had worsening tension once the treatment had
been completed.
Prior to RCT, there were significant correlations among the
EGM-thresholds and morphology (r=-0.719, p<0.05) as well as
vascularisation of fPap (r=-0.719, p<0.05). Once RCT had been
initiated, a strong positive correlation was only detected between EGM
and vascularisation (r=0.763, p<0.05) one week subsequent to
the initiation of therapy. In the follow-up measurements, no additional
correlations were observed.
Discussion
In the current study, we demonstrated that an improvement in EGM
thresholds does not occur concurrent to the morphology and
vascularisation of fPap. Vascularisation is the first parameter that
appears to show signs of improvement. A further important result is that
additional deterioration of EGM-thresholds appears to occur even after
the RCT treatment has been completed. Our findings support the theory
that when nerve fibres responsible for innervating taste buds are
damaged by irradiation, taste cells could be indirectly destroyed due to
the fact that mature taste cells need functional nerve contact in order
to be maintained [8].
After receiving RT treatment for HNC, patients commonly complain of
taste dysfunction [1]. When receiving a 6-8-week daily radiotherapy
course, a loss of taste generally manifests by weeks 3 to 4 and it is
common for all taste modalities to be impacted. Previous studies have
reported the worsening of EGM-thresholds during RCT for HNC [3]. The
time at which taste cells are lost predominantly occurs when patients
begin to experience functional taste loss, which is initially seen one
week into the course of radiotherapy [9].
Low-level radiation delivered during the early stages could cause the
receptors to be damaged. In a study, it was observed that when curative
radiation therapy was given for HNC, salivary function had decreased by
the end of week 1, and measurements clearly indicated that after the
second week of treatment, taste function had been impaired [9].
Initial evaluations of taste changes reported by patients receiving
radiation therapy have indicated that significant changes occur when the
treatment is ongoing, and that taste sensations do not return to
pre-treatment levels [1]. Such taste problems could be caused by
direct impacts on the taste receptors, the reduction in the production
of saliva leading to secondary infection, and limited delivery of
tastants to receptor areas.
With regard to chemotherapy, taste disorder aetiology is not only
because of damage caused to taste receptors and neurons by RCT, but it
is probable that it is caused by multiple factors. Apart from
chemotherapeutic agents, other drugs can also alter taste and must be
taken into account when assessing taste in such patients [10].
In summary, there is no improvement in EGM-thresholds concurrent with
the morphology and vascularisation of fPap. There has been minimal focus
in the literature on taste dysfunction in patients with HNC, and it is
probable that they are underestimated. Additional long-term studies of
nerve fibres at the tongue tip subsequent to chemotherapy or
radiotherapy in patients diagnosed with tonsillar squamous cell
carcinomas are therefore necessary.