Evaluating the etiology of metallic taste during head and neck cancer treatments: a study of facial and glossopharyngeal nerve interactions.

Metallic Taste (MT) is frequently described during head and neck cancer treatments but very little is known about its etiologies. One hypothesis to explain the MT is the removal of facial nerve inhibition on the glossopharyngeal nerve. Indeed, the decrease of taste afferents mediated by the facial nerve (anterior two-thirds of the tongue) due to cancer or its treatments, would reveal those mediated by the glossopharyngeal nerve (posterior one-third of the tongue) and thus lead to MT perception. The aim of this study was to evaluate the validity of this hypothesis. Selective supraliminar taste tests on the tip and the base of the tongue were regularly performed on 44 patients with head and neck cancers before, during, and after their treatment. Sweet, salty, bitter, sour, and MT were tested. Patients were grouped based on whether they reported experiencing MT or not. Twelve patients complained about MT (27.2 %), always during the treatment phase. Most of them (83.3 %) were treated by surgery and radiotherapy or radiochemotherapy. Supraliminar tastes were altered in every patient, especially during the treatment phase. Test results showed that perceived intensity was significantly reduced in patients reporting MT for salt, sweet and sour. This was observed more on the base of tongue than on the tip of the tongue. MT was significantly linked with mucositis (p = 0.027) but with neither candidiasis (p = 0.38) nor salivary flow (p = 0.63). The hypothesis of removal of facial nerve inhibition on the glossopharyngeal nerve cannot explain MT in head and neck cancer.