Erythemal and therapeutic response of psoriasis to PUVA using high-dose UVA.

In PUVA treatment of psoriasis, clinical observation suggests that uninvolved skin is more susceptible to PUVA erythema than lesions of psoriasis. If this is the case, then the efficacy of PUVA treatment might be increased by using localized high-dose UVA restricted to lesional skin. We have therefore studied the erythemal and therapeutic response of psoriasis to PUVA using high-dose UVA and, for comparison, the erythemal response to UVB. In 14 patients, an area of psoriasis and adjacent uninvolved skin were exposed to a series of UVA doses (350 +/- 30 nm, 1-16J/cm2), using an irradiation monochromator. Six other patients were similarly phototested with a series of UVB doses (300 +/- 5 nm, 20-112 mJ/cm2) to both uninvolved and lesional skin. Erythema was judged visually at 72 h for psoralen-UVA, and at 24 h for UVB, and measured using a scanning laser-Doppler velocimeter. In 10 patients, PUVA therapy using high-dose UVA was subsequently given to lesional skin (8-16J/cm2 twice weekly) in addition to conventional whole-body PUVA. For psoralen-UVA, the minimal phototoxic dose within psoriasis was increased by a factor of 4 compared with non-lesional skin (P < 0.01, Wilcoxon signed-rank test). For UVB, the minimal erythema dose within psoriasis was higher than that for non-lesional skin (medians > 112 and 28 respectively, P < 0.05). Laser-Doppler measurements confirmed that the reduced erythemal sensitivity was not due to masking of response by pre-existing increased blood flux within psoriasis.(ABSTRACT TRUNCATED AT 250 WORDS)