Long- and short-term histological observations of congenital nevi treated with the normal-mode ruby laser.

OBJECTIVE: To evaluate histologically the long- and short-term changes associated with cosmetic improvement or failure of normal-mode ruby laser treatment of patients with congenital nevi. DESIGN: A biopsy of the laser-treated lesions of 10 patients with good or poor cosmetic results was performed at periods up to 8 years 10 months after treatment (mean, 4 years 9 months). Short-term findings were evaluated in 3 patients. SETTING: Ueda Setsuko Clinic and the Dermatology Unit of the Kyushu University, Fukuoka, Japan. PATIENTS: Of the 85 Japanese patients with relatively large congenital nevi who had been treated with the normal-mode ruby laser since 1990, 13 gave informed consent for biopsy and histological examination of the treated area. RESULTS: A long-term follow-up study of the 8 patients with good cosmetic results showed the presence of residual nevus cells 1.11 +/- 0.35 mm (mean +/- SD) (range, 0.63-2.05 mm) below the skin surface. Above these cells was a layer of connective tissue that formed a subtle microscopic scar that preserved the normal structure of the papillary dermis. Hair follicles were damaged at the base, and the hairs were attenuated. However, in the 2 patients with poor cosmetic results, nests of pigmented cells were commonly seen in the epidermis, and melanin was relatively abundant in basal keratinocytes. No malignant changes were observed in any patient. A short-term study in 3 patients showed damage to pigmented cells in the epidermis and upper dermis as observed following electrodesiccation. CONCLUSIONS: Multiple treatments with the normal-mode ruby laser produced immediate thermal damage to the superficial nests of nevus cells and a subsequent remodeling of the superficial connective tissue. When the thickness of the subtle microscopic scar reached 1 mm, it masked the underlying residual nevus cells and achieved a good cosmetic result. Follow-up for at least 8 years after laser treatment showed no evidence of malignant change in the treated areas.