Selective accumulation of lipid within melanocytes during photochemotherapy (PUVA) of psoriasis.

In patients undergoing photochemotherapy (PUVA) a selective accumulation of lipid droplets was observed within the cytoplasm of melanocytes. Keratinocytes did not develop lipid droplets. Within 2 months after clearing of psoriasis the droplets gradually vanished and did not reappear even during maintenance PUVA therapy. Increased intracellular lipid deposits are usually taken to herald cell degeneration. Since the maximum lipid accumulation coincided with the end of the clearing phase when melanin production was at its height, the intramelanocytic lipid may have been a morphological sign of over-stimulation of melanocytes, which could eventually result in melanocyte destruction. Since excess melanin may be cytotoxic for melanocytes this may explain the irreversible hypopigmentation which develops in some patients treated with PUVA.