Phototoxic and photoallergic dermatitis caused by hydroxychloroquine

Hydroxychloroquine (HCQ) is a lysosomotropic amine used in rheumatology and dermatology for its immunosuppressive and photoprotective properties. The side effects of synthetic antimalarials are well known, although not frequent. They can involve the gastrointestinal, ocular, haematopoietic, cardiovascular, auditory and central nervous system. Among adverse cutaneous reactions, bluish-grey to black discoloration is the most common, while a more or less persistent phototoxicity is very unusual. However, both phototoxic and photoallergic mechanisms may be proposed for the itchy erythemato-papulo-squamous hyperpigmented dermatitis involving only the light-exposed areas of the face and hands observed by us in a 74-year-old man with skin phototype IV treated with HCQ for 1 year for rheumatoid arthritis. Hyperpigmentation of involved skin, localization of lesions, their slow resolution, and persistence of photosensitivity for some months are suggestive of a phototoxic reaction, while the positive photopatch test reaction to HCQ and its persistence with time allow the advance of a photoallergic mechanism. The positive reaction only after exposure to UVB is not reported in literature.