[Photosensitization after intramuscular injections of hematoporphyrin. 3 cases]

Haematoporphyrin is a synthetic porphyrin the photosensitizing properties of which are used for the detection and treatment of some neoplasias. Three cases of phototoxicity from Hemedonine, an "anti-asthenia" drug composed of pure haematoporphyrin, are reported. Following exposure to the sun, painful urticarial plaques developed at the sites of intramuscular injections, and spread to the lumbar and abdominal regions, leaving a brownish pigmentation which persisted for years. Photobiological exploration was performed in one of these patients, demonstrating photosensitivity to Hemedonine in vivo and showing that long UVA rays were essentially responsible for the lesions. Histological examination elicited the initial vascular changes of a phototoxic reaction and suggested a new mechanism of photosensitization: "photo-induced immune vasculitis". The phototoxic effects of haematoporphyrin are primarily due to the destruction of intracellular organelles consecutive to oxidative denaturation of membrane systems. The initial phase of the phototoxic reaction might consist of complement activation and degranulation of dermal mast cells.