Method: Control healthy subjects (n=36), BMS (n=24) and LNI (n=47) patients rated their pain levels using the visual analogue scale (VAS; 0 = no pain and 10 = worse pain imaginable) at rest and, post cold-stimulant ethyl chloride (EC) application followed by heat-stimulant capsaicin exposure (10μg/ml) on the anterior two-thirds of the tongue. Cool, warm, cold pain and heat pain perception thresholds were then measured by QST testing using the TSA 2001-II Advanced (MEDOC®, Israel) neurosensory analyser and Classic Method of Limits. Patients held a 5x5mm intraoral thermal probe gently in contact with the target area of the tongue. Baseline temperature of the thermode was set at 32°C, with gradual elevation or reduction within 0°C and 50°C cut-off limits. Average thermal thresholds were compared between the groups using t-Tests, where p<0.05 indicated statistical significance.
Results: BMS patients significantly reported the most pain at rest (p<0.001) and capsaicin hypersensitivity (p<0.01). Despite their increased sensitivity to capsaicin and a statistically significantly lower warm threshold than the controls (p<0.05), these patients did not show heat pain hyperalgesia. BMS patients also indicated increased sensitivity to EC and cold pain allodynia (p<0.05), compared to significantly reduced or, no cold or heat pain sensation amongst LNI patients (p<0.01).
Conclusion: Capsaicin and EC sensitivity assessment coupled with QST testing are useful for detecting hyperalgesia and hypoalgesia amongst BMS and LNI patients. Future studies should compare the Method of Limits with the Method of Levels, whereby set temperatures are tested in the latter method.