Intradermal capsaicin as a neuropathic pain model in patients with unilateral sciatica

Abstract

AIM: This study compared the responses between patients with unilateral sciatica and pain-free volunteers following administration of intradermal capsaicin. METHODS Fourteen patients with unilateral sciatica and 12 pain-free volunteers received one injection per hour over 4h of 1μg and 10μg capsaicin, into each calf. For each dose, spontaneous pain (10cm VAS), area of flare (cm 2) and the sum of allodynia and hyperalgesia radii across eight axes (cm) were recorded pre-injection and at 5, 15, 30, 45 and 60min post injection. RESULTS: Sciatica subjects experienced higher spontaneous pain and hyperalgesia responses in both legs compared with pain-free volunteers. The largest mean difference in spontaneous pain was 2.8cm (95% CI 1.6, 3.9) at 5min in the unaffected leg following 10μg. The largest mean difference in hyperalgesia was 19.7cm (95% CI 12.4, 27.0) at 60min in the unaffected leg following 10μg. Allodynia was greater in patients than in controls with the largest mean difference of 2.9cm (95% CI 1, 4.8) at 5min following 10μg in the affected leg. Allodynia was also higher in the affected leg compared with the unaffected leg in sciatica patients with the highest mean difference of 3.0cm (95% CI 1.2, 4.7) at 5min following 10μg. CONCLUSIONS: The responses to intradermal capsaicin are quantitatively and qualitatively different in unilateral sciatica patients compared with pain-free controls. © 2011 The Authors. British Journal of Clinical Pharmacology © 2011 The British Pharmacological Society.