• After the initial clearing phase, the mean rate of treatment with psoralen and ultraviolet-A (PUVA) radiation among 839 patients with psoriasis was 29.6 treatments a year during an average of 18.6 months. The initial percentage of skin surface involved with psoriasis was the single best indicator of the rate of treatment needed. The previous use of other therapies and the presence of certain environmental factors (eg, isomorphic response to injury, leisure time spent mostly indoors, and cold weather having no effect on psoriasis) were associated with additive increases in rate. Patients with none of these factors had an average of 5.4 treatments a year less than was predicted by the extent of skin involvement alone, whereas patients with previous use of four or more therapies and three environmental factors had 10.4 more treatments a year.
(Arch Dermatol 1982; 118:404-408)
Melski JW, Stern RS. Annual Rate of Psoralen and Ultraviolet-A Treatment of Psoriasis After Initial Clearing. Arch Dermatol. 1982;118(6):404-408. doi:10.1001/archderm.1982.01650180038013