Phototherapy reduces the number of epidermal and CGRP-positive dermal nerve fibres

The purpose of this study was to gain an understanding of why phototherapy relieves itching. Skin samples (3mm punch biopsies) from non-inflamed gluteal skin of 10 patients undergoing phototherapy were compared before and after 20 treatments. All the cutaneous nerve fibres were visualized by antibodies against PGP 9.5, sensory nerve fibres by antibodies against calcitonin gene-related peptide (CGRP) and capsaicin-sensitive primary nociceptive afferents by antibodies against VR1-receptor. Following treatment, the number of PGP 9.5-positive nerve fibres in the epidermis was reduced from 193 +/- 52 to 102 +/- 34 (p < 0.0001) and the number of CGRP-immunoreactive nerve fibres, which occurred only in dermis, was reduced from 28 +/- 15 to 22 +/- 7 (p = 0.04). The VR1-immunoreactive nerve fibres, some of them containing immunoreactivity to CGRP, were not affected. The success of phototherapy in combating itch may at least partly be linked with the reduction in the number of epidermal nerve fibres. The reduction in the number of CGRP-immunoreactive nerve fibres in the dermis may contribute to the beneficial effects of UV irradiation on the inflammatory process.