A semiquantitative light and electron microscopic analysis of histopathologic changes in photochemotherapy-induced freckles.

Photochemotherapy(PUVA)-induced freckles were found in 25 patients (41%) who had received more than 1,000 J/cm2 of PUVA. The patients had been treated with PUVA for more than 2 years, with more than 150 exposures before PUVA lentigines appeared on the thighs, the upper arm, the mid-lower arm, the waist, and the buttocks. The histopathology of these freckles was analyzed by light and electron microscopy. Light microscopy showed an increased amount of pigment and melanophages and increased numbers and size of melanocytes. The keratinocytes often displayed atypical features such as enlarged nuclei, giant size, or fibrillar degeneration. Homogenization of the papillary dermis was observed in 11 patients. The activation of melanocytes was confirmed electron microscopically, and pathological features such as large amounts of lipid droplets and lysosome-melanosome complexes within the melanocytes were seen. The Langerhans cells were mostly normal, whereas the keratinocytes showed cytolytic changes, fibrillar degeneration, and vacuolization. A close follow-up of patients with prolonged PUVA treatment is recommended.