[Value of the light-test histological study in photodermatoses]. / Intérêt de l'étude histologique du phototest dans les photodermatoses.

ABSTRACT

Clinic and histologic analysis of 92 phototests of various photodermatosis (14 benign summer light eruption (BSLE), 47 polymorphous light eruption (PMLE) 20 persistent light reactor photodermatitis (PLRP), 11 drug induced photodermatitis (DIP) has been performed. Clinically, a phototoxic aspect was observed in 30 cases, it was photoallergic in 36 cases and uncertain in 26 cases. Histologically, a phototoxic picture was present in 32 cases, a photoallergic one in 48 cases, and 12 cases exhibited unclassified aspect. Only one case of BSLE was associated with photoallergic aspect, clinically and histologically. Photoallergic type was observed in 70 p. 100 of iterative exposure phototest (IEP) of PMLE; clinical and histological aspects were concordant; in contrast phototoxic aspects were constantly observed when single exposure phototest (SEP) were used. In PLRP histological aspect of IEP was constantly of photoallergic type; whereas clinical aspect was uncertain in 50 p. 100 of the cases; 7 of the 10 biopsies of SEP exhibited a photoallergic picture. In DIP histological aspect of IEP was constantly photoallergic, whereas 5 of the 6 cases exhibited uncertain clinical aspect; only one of the 5 SEP gave a photoallergic reaction both clinically and histologically. Comparison of histological features revealed a more typical photoallergic picture in PLRP than in PMLE. We conclude that the reproducibility of clinical and histological lesions is better with the iterative exposure phototest than with single exposure phototest; histologic examination is more reliable than clinical findings in persistent light reactor photodermatitis and drug induced photodermatitis.