Capsaicin 8% patch reversibly reduces A-delta fiber evoked potential amplitudes

Introduction: The capsaicin 8% patch is a treatment option in patients with localized peripheral neuropathic pain. Better understanding of its mechanisms of action and knowledge on predictive biomarkers for a treatment response is warranted. Objectives: To use electrically evoked pain-related potentials for investigation of A-delta fiber conduction after capsaicin 8% patch treatment. Methods: We studied 11 healthy controls at the dorsal hand and the foot and 12 patients with neuropathic pain at the area affected by neuropathic pain before and 2 hours after application of a capsaicin 8% patch (Qutenza). Patients were additionally phenotyped using quantitative sensory testing and skin biopsy. Results: Peak-to-peak N1-P1 amplitudes (PPA) were reduced after Qutenza application by a median of 60% in 6/11 controls and by 33% in patients with neuropathic pain compared with baseline; they were increased in 3 controls that did not develop capsaicin-induced pain. Patients with elevated cold detection thresholds more often had reduced PPA after Qutenza than those with normal cold detection threshold. Patients with reduced PPA after capsaicin application and with capsaicin-induced pain were more likely to achieve pain reduction on Qutenza. Conclusion: The capsaicin 8% patch induces a reduction in A-delta PPA in healthy persons and in patients with neuropathic pain adding to the mechanistic understanding of its effect.