[Keratosis lichenoides chronica and prolonged exposure to infrared radiation].

BACKGROUND: We report a case of keratosis lichenoides chronica and prolonged exposure to a source of heat (infrared radiation). CASE REPORT: A 35 year-old man was examined for a symmetric and reticulate dermatosis on the abdomen, the interior of arms and lower extremities. The lesions had progressed over several months. They were characterized by hyperpigmentation, erythematous, bullous and squamous papules. These lesions were associated with those of the scalp, evoking seborrheic dermatitis. The patient was exposed to a source of heat with an electric radiator on his bare chest everyday. The skin biopsy showed a lichenoid reaction. All these elements allowed to put the diagnosis of keratosis lichenoides chronica, probably actived by the infrared light. DISCUSSION: Keratosis lichenoides chronica is a rare acquired dermatosis of the young adult. Its physiopathology remains elusive. This dermatosis is characterized by keratosic violaceous lichenoid papules distributed symmetrically. The eruption is usually asymptomatic. The histological examination indicates a lichenoid reaction. The progression is chronic and the disease is very resistant to therapy. Keratosis lichenoides chronica has never been described as being able to be induced by Koebner's phenomenon. In the literature, two cases of erythema ab igne were associated with lichen planus. For some authors, keratosis lichenoides chronica is an entity itself, for others it would be related to lichen planus. These arguments enabled us to diagnose keratosis lichenoides chronica probably activated by the infrared light.