Assessment of Somatosensory Function, Pain, and Unpleasantness in Two Surrogate Models of Trigeminal Nerve Damage : A Randomized, Double-Blind, Controlled Crossover Study

Aims: To assess the pain and/or unpleasantness and the somatosensory changes caused by two experimental models of trigeminal nerve damage (topical application of capsaicin and local anesthetics) in healthy participants using extensive evaluation tools. Methods: This double-blinded, randomized, placebo-controlled, crossover study included 20 healthy adult participants who underwent three separate sessions of testing. In each session, the psychophysical quantitative sensory testing (QST) and the electrophysiologic electrically evoked trigeminal "nociceptive-specific" blink reflex (nBR) investigations were performed at baseline. Following a 15-minute topical application of 0.1% capsaicin, 5% EMLA, or Vaseline (placebo) agents, the maximum numeric rating scale pain and unpleasantness scores were recorded. Additionally, qualitative sensory testing and somatosensory mapping were performed. The QST and nBR investigations were repeated immediately after each application. Data were analyzed using repeated-measures analysis of variance. Results: Capsaicin application was associated with significantly higher pain and unpleasantness scores when compared to EMLA and Vaseline (P < .001), with varied bidirectional somatosensory changes among the participants and significant loss of thermosensory function (P < .030). EMLA application induced loss of thermal and mechanical somatosensory function (P < .030) and a significant reduction in electrically evoked pain scores on nBR investigation (P < .001). No significant changes were seen in the electrophysiologic component of the nBR after any of the applications (P = .922). Conclusion: Topical capsaicin and EMLA application mimicked certain aspects of somatosensory changes seen in trigeminal nerve damage patients and may be used as surrogate models of such changes.

blink reflex; capsaicin; EMLA; quantitative sensory testing; trigeminal nerve damage

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