Erythemal and pigmentary phototest reactions in polymorphic light eruptions.

The erythemal and pigmentary skin reactions in 110 patients with chronic polymorphic light eruptions (PMLE) and in 154 control persons were investigated by phototesting with a medium pressure mercury lamp. Recording the erythemal threshold (MED) at 2-h intervals for up to 24 h after irradition disclosed no differences between PMLE patients and controls. There was, however, a tendency for the erythemal reaction to subside more slowly in the PMLE patients; this tendency reached a statistically very significant level by day 7. Seventy-three per cent of the PMLE patients and 86% of the controls showed immediate pigmentation. Three days after irradiation, however, 91% of the PMLE patients showed a delayed pigmentary response, in contrast to 66% of the controls; the depth of pigmentation was also greater in the PMLE patients. This study demonstrates that although PMLE patients and healthy controls, taken as groups, may show some differences in their erythemal and pigmentary response, the measurement of the these reactions is of no immediate assistance in the diagnosis of individual cases of polymorphic light eruptions.