Neurogenic Mechanisms in Burning Mouth Syndrome

Burning mouth syndrome (BMS) is characterized by a bilateral burning sensation in the anterior tongue, hard palate and lips in the absence of any clinical or laboratory findings. The term syndrome implicates the simultaneous presence of oral dryness (xerostomia) and altered taste (dysgeusia) in addition to the burning sensation in the oral mucosa. BMS is most often seen in women and is more frequent during menopause. The etiology and pathogenesis are still unclear but recent studies suggest that BMS is a neuropathic pain condition. The objectives of the study are: * To clarify potential neurogenic mechanisms behind BMS using immunohistochemistry (IH) to characterize the localization and distribution of peripheral nerve fibres, neuropeptides like substance P, calcitonin gene-related peptide, nerve growth factor, nerve growth factor receptor, PGP 9.5 neuronal marker and TRPV1 as well as inflammatory/structural changes. * To perform a randomized double blind cross-over intervention study to examine the efficacy and safety of topical application of capsaicin oral gel (on the tongue) to relieve the burning sensation in patients with BMS.

Data which support the hypothesis that BMS is a neuropathic pain condition include amongst others a recent clinically controlled study that has shown up-regulation of TRPV1-positive nerve fibres in tongue mucosa in patients with BMS. The vanilloid receptor-1 (TRPV1) is a voltage-dependent cation channel expressed by the unmyelinated C-nociceptive nerve fibres and the receptor may be activated by capsaicin (from chili peppers), heat and H+. Capsaicin binds to the TRPV1 receptor causing depolarization of the C-nociceptors. Prolonged activation of these neurons by capsaicin depletes pre-synaptic substance P and makes them unable to report pain.