Ex vivo quality-switched ruby laser irradiation of cutaneous melanocytic lesions: persistence of S-100-, HMB-45- and Masson-positive cells.

AIM: To assess changes in human pigmented melanocytic skin lesions after quality-switched ruby laser (QSRL) irradiation.

METHODS: Investigations were performed ex vivo on 21 melanocytic pigmented lesions (10 nevus cell nevi, 2 pigmented dermal nevi, 4 congenital nevi, 3 lentigo maligna lesions, 2 superficial spreading melanomas) immediately after surgical excision. A total of 42 biopsy specimens was obtained for comparative investigations before and after QSRL impact. Electron microscopy was performed in 3 lesions.

RESULTS: Hematoxylin-eosin stainings showed selective vacuolization of pigmented structures (melanin granules, melanophages, pigmented melanocytes, pigmented keratinocytes) immediately after QSRL irradiation due to selective photothermolysis. Cryosections stained with nitroblue tetrazolium chloride featured minimal thermal damage of the surrounding tissue proving the high selectivity of QSRL light. Immunohistochemical techniques employing anti-S-100, HMB-45 antimelanoma antibody and Fontana-Masson staining revealed selective photothermal damage (vacuolization) of basal melanin granules, pigmented basal melanocytes and epidermal keratinocytes, as well as pigmented superficial dermal melanocytes. Deeper melanocytes and nests of nonpigmented melanocytes persisted unaltered and retained their S-100 and HMB-45 positivity. Masson's staining revealed persisting dermal melanophages. Electron microscopy showed specific damage of both keratinocytes and melanocytes with numerous melanosomes and confirmed the light-microscopic findings. Deeper dermal melanocytes containing only few melanin granules remained unaltered.

CONCLUSION: In pigmented lesions extending into the dermis, deeper pigmented melanocytic cells (nevus cells) persist throughout a single course of QSRL exposure. Nonpigmented melanocytic cells remain totally unaffected by QSRL irradiation. Therefore QSRL therapy of melanocytic nevi and congenital nevi should only be performed in controlled studies. Long-term results have to be evaluated before recommendations can be given.