Plasma 5-S-cysteinyldopa as an index of melanogenesis

Plasma 5-S-cysteinyldopa (5-S-CD) concentration measured in healthy volunteers in Edinburgh, Scotland (latitude 56 degrees N) showed only minor changes during the day. However, when measurements were performed over a 12-month period a significant rise in 5-S-CD concentration was found. Skin pigmentation and hair colour were not related to plasma 5-S-CD levels. Patients with psoriasis treated with ultraviolet-B or photochemotherapy (PUVA) developed an almost two fold increase in their plasma 5-S-CD level within the first five treatments, before pigmentation developed, subsequent increments of up to four times the pretreatment level being found in the PUVA group. Dithranol treatment caused an increase in plasma 5-S-CD in some psoriatic patients, suggesting a possible association between skin erythema and elevated 5-S-CD levels. The value of plasma 5-S-CD in the follow-up of patients with malignant melanoma does not seem to be invalidated by unavoidable exposure of the subjects to sunlight in a temperate climate such as that of South East Scotland.