Profiling intraoral neuropathic disturbances following lingual nerve injury and in burning mouth syndrome.

BACKGROUND: The aim of the study was to analyse intraoral neurophysiological changes in patients with unilateral lingual nerve lesions as well as patients with Burning Mouth Syndrome (BMS) by applying a standardized Quantitative Sensory Testing (QST) protocol. METHODS: The study included patients suffering from a peripheral lesion of the lingual nerve (n = 4), from BMS (n = 5) and healthy controls (n = 8). Neurophysiological tests were performed in the innervation areas of the tongue bilaterally. For BMS patients the dorsal foot area was used as reference. RESULTS: For patients with peripheral lesion of the lingual nerve the affected side of the tongue showed increased thresholds for thermal (p < 0.05-0.001) and mechanical (p < 0.01-0.001) QST parameters, indicating a hypoesthesia and thermal hypofunction. In BMS patients, a pinprick hypoalgesia (p < 0.001), a cold hyperalgesia (p < 0.01) and cold/warmth hypoesthesia (p < 0.01) could be detected. CONCLUSIONS: The results of this study verified the lingual nerve lesion in our patients as a peripheral dysfunction. The profile showed a loss of sensory function for small and large fibre mediated stimuli. A more differentiated classification of the lingual nerve injury was possible with QST, regarding profile, type and severity of the neurologic lesion. BMS could be seen as neuropathy with variable central and peripheral contributions among individuals resulting in chronic pain.

The Detection of Small-Fiber Neuropathies in Burning Mouth Syndrome and Iatrogenic Lingual Nerve Injuries: Use of Quantitative Sensory Testing.

AIMS: To assess thermal pain perception in patients with burning mouth syndrome (BMS) and lingual nerve injury (LNI) by using a quantitative sensory testing (QST) protocol. METHODS: QST was used to assess cool, warm, cold pain, and heat pain thresholds in healthy control subjects (n = 17) and in patients with BMS (n = 22) and LNI (n = 47). Capsaicin (10 µg/mL) and ethyl chloride-evoked hypersensitivities at the anterior two-thirds of the tongue were measured using a visual analog scale. Data were analyzed using Microsoft Excel with descriptive statistics, scatter graphs, and two-tailed Student t tests with 95% confidence interval and 5% level of significance. RESULTS: Patients with BMS significantly reported the most pain at rest (P < .001) and capsaicin hypersensitivity (P < .01). Despite this increased sensitivity to capsaicin and significantly lower warm threshold than the control subjects (P < .05), these patients did not show heat pain hyperalgesia. There was increased sensitivity to ethyl chloride and cold pain hyperalgesia in patients with BMS (P < .05) compared with reduced or no sensation of cold or heat pain in patients with LNI. CONCLUSIONS: This study has demonstrated that the assessment of capsaicin and ethyl chloride-evoked sensitivities as well as the use of QST to assess thermosensitivity are useful approaches for detecting hyperalgesia or hypoalgesia to heat and cold in patients with BMS and LNI.

Disruption of oral sensory relay to brain increased anxiety- and depression-like behaviours in rats.

OBJECTIVE: Sensory information plays an important role to determine psycho-emotional behaviours of individuals. Lingual nerve can be damaged by dental surgery or trauma, such as physical irritation, radiation, chemotherapy, or viral infection. This study was conducted to examine the psycho-emotional effects of lingual nerve damage in which oral sensory relay to the brain is disrupted. DESIGN: Male Sprague-Dawley rats were tested for anxiety and depression-related behaviours after bilateral transections of the lingual and chorda tympani nerves (Nx) or sham operation. Tissue contents of serotonin and its metabolite in the hippocampus, hypothalamus, and nucleus accumbens were analyzed by high-performance liquid chromatography. RESULTS: Sucrose preference was reduced in Nx rats compared with sham rats, suggesting the development of anhedonia, decreased pleasure seeking behaviour, by the lingual nerves transection. Ambulatory activity was decreased, anxiety-related behaviours during the activity test increased, time spent in the open arms during elevated plus maze test decreased, and immobility duration during forced swim test increased in Nx rats compared with sham rats. Serotonin level in the hippocampus of Nx rats was decreased significantly compared with sham rats. CONCLUSIONS: Results suggest that aberration of oral sensory relay to brain may lead to the development of depression- and anxiety-related disorders, and decreased serotonergic neurotransmission in the hippocampus may play a role in its underlying mechanism.

Capsaicin avoidance as a measure of chemical hyperalgesia in orofacial nerve injury models.

Many patients suffer from trigeminal neuralgia and other types of orofacial pain that are poorly treated, necessitating preclininal animal models for development of mechanisms-based therapies. The present study assessed capsaicin avoidance and other nocifensive behavioral responses in three models of orofacial nerve injury in rats: chronic constriction injury (CCI) of the mental nerves, partial tight ligation of mental nerves, and CCI of lingual nerves. We additionally investigated if nerve injury resulted in enhanced capsaicin-evoked activation of neurons in trigeminal caudalis (Vc) or nucleus of the solitary tract (NTS) based on expression of Fos-like immunoreactivity (FLI). Mental nerve CCI resulted in an enhancement of capsaicin avoidance in a two-bottle preference paradigm, while neither mental nerve injury produced thermal hyperalgesia or mechanical allodynia. CCI of lingual nerves did not affect capsaicin avoidance. Counts of FLI in Vc were significantly higher in the lingual sham and mental nerve CCI groups compared to mental shams; FLI counts in NTS did not differ among groups. Mental nerve CCI may have induced central sensitization of chemical nociception since increased capsaicin avoidance was accompanied by greater activation of Vc neurons in response to oral capsaicin.

Lingual nerve paralysis after endobronchial ultrasound utilizing laryngeal mask airway.

A 52-year-old woman developed loss of sensation and taste in the anterior two thirds of her tongue after undergoing endobronchial ultrasound-guided transbronchial needle aspiration using a laryngeal mask airway (LMA). This was believed to be due to bilateral lingual nerve injury, likely caused by stretching of tissue of the upper airway because of repetitive movements of LMA during attempts to obtain a clearer ultrasound image to direct needle insertion. To the best of our knowledge, this is the first report of lingual nerve injury after an endobronchial ultrasound procedure using LMA.

Evaluation of tongue sensory disturbance by somatosensory evoked magnetic fields following tongue stimulation.

Quantitative measurement is required in clinical situation for sensory disturbance of the tongue due to lingual nerve injury. To assess disabled sensory function of the tongue, somatosensory evoked magnetic fields (SEFs) were measured following electric tongue stimulation in 13 patients with sensory disturbance by unilateral lingual nerve injury and in 10 age-matched healthy volunteers. Affected- and healthy-sides of the tongue were stimulated separately with the same intensity. Although the healthy-side stimulation induced clear responses over the contralateral hemisphere of all participants, the affected-side stimulation evoked hardly traceable responses in 6 patients and no activity in the remaining 7 patients. We evaluated the cortical activity via activated root-mean-square (aRMS), which is the time-averaged activity between 10 and 150 ms from the 18-channel RMS over the contralateral hemisphere. The laterality index of aRMS, expressed as [(left-right)/(left+right)], was out of the pre-defined normal range (-0.287 to 0.337) in 12 patients, and within the range in all healthy volunteers. The test sensitivity and specificity of the procedure were 92.3% and 100%, respectively. Tongue SEFs are reproducible and objective method to evaluate sensory disturbance of the tongue.