Application of an 8% capsaicin patch normalizes epidermal TRPV1 expression but not the decreased intraepidermal nerve fibre density in patients with brachioradial pruritus.

BACKGROUND: Topical capsaicin shows efficacy in the treatment of brachioradial pruritus (BRP); however, its mechanisms of action remain unclear.

OBJECTIVE: The effect of capsaicin on the epidermis (i.e. peripheral expression of non-neuronal sensory receptors on keratinocytes, morphological changes in innervation) is still unknown. We aimed to investigate the effect of topical capsaicin on keratinocyte expression of TRP channels and on the intraepidermal nerve fibre density (IENFD) in patients with BRP.

METHODS: Thirty-one patients with BRP received an 8% capsaicin patch. Biopsies in lesional and non-lesional skin were taken to assess epidermal morphology, keratinocyte expression of TRP channels and IENFD before and 3 weeks after treatment.

RESULTS: Treatment with the capsaicin patch led to a significant decrease in itch and paresthetic symptoms (P < 0.05). Keratinocyte morphology is unaltered after capsaicin therapy. Reduced keratinocyte expression of TRPV1 in lesional skin (P = 0.009; n = 9) normalized 3 weeks after treatment (P = 0.016; n = 10), but not the IENFD, which remained reduced in lesional epidermis.

CONCLUSION: The normalization of the decreased TRPV1 expression may account for the effectiveness of topical capsaicin, which does not reconstitute the reduced IENFD, arguing for a role of epidermal TRPV1 in the maintenance of BRP.