PUVA therapy for polymorphous light eruptions: comparison of systemic methoxsalen and topical trioxsalen regimens and evaluation of local protective mechanisms.

Twenty-six patients with long-standing, recurrent polymorphous light eruptions were treated with psoralen photochemotherapy. Thirteen patients received oral methoxsalen, while 13 were photosensitized by trioxsalen baths. After an average of 20 PUVA exposures, a good or excellent therapeutic result was achieved in 12 of the orally treated and 10 of the topically treated patients. In most of the cases, clinical desensitization lasted throughout the summer season, without further PUVA exposures. When the polymorphic phototest reaction (PPR) was registered 72 h after skin testing with a medium pressure mercury lamp, a remarkable reduction or total abolition of the reaction was seen in tests made on PUVA-exposed skin, as compared with tests made on a comparable skin site, shielded from UVA exposure during the treatments. A concomitant decrease in the erythemal reactivity (MED) of the skin was usually--though not invariably--seen. It is concluded that in addition to including an increase in the shielding properties of stratum corneum, PUVA treatment may induce non-responsiveness in PMLE skin by other, possibly anti-inflammatory or immunological mechanisms.