Photoallergy clinical features diagnosis and treatment

Photoallergy clinical features diagnosis and treatment

Photoallergy is a cutneous hypersensitivity to exogenous drugs and/ or chemicals in the presence of radiant energy. The participation of the immune system is necessary for the response to occur and photons are required along with the chemicalbfor immunologic activation. Although wavelength within the UVB spectrum have been implicated in some photoallergic reactions, however in most cases UVA is responsible. The electromagnetic energy converts an immunologically inactive form of the photosensitizing compounds into its active form, the hapten. This hapten is stable photoproduct of the chemical. It combines with a protein in the skin to produce full antigen. This antigen elicts a cell mediated immune response. The involvement of the immune system is demonstrable by passive transferability. The chemicals responsible for inducing photoallergy are haloginated salicylanilides, halogenated phenols, sulphalinamide, sulphonyl ureas, thiazides, and musk ambrette etc.

Clinical features The initial few exposures to light are asymptomatic which result only sensitization to the photoallergen. Subsequent exposures result in eczematous eruption characterized by cardinal clinical features of acute eczema, namely erythema, edema, vesiculation, oozing, and crusting. This eruption is localized to ares exposed to the sunlight namely the forehead, nose, malar areas, rims of the ears, sides and back of the neck, V of the chest, and extenser surface of the forearms, hands, shins and feet. The sparing of shielded ares is also characteristic. These ares include the retroauricular ares, the submental region, uppereyelids, back of the neck, nasolabial folds, and the flexor aspects of the limbs, and other deeply recessed body folds.

Diagnosis The history and clinical examination supplemented by histopathology and photopatch test are helpful in diagnosis. The histopathological examination reveals the (1) intracellular edema in the epidermis with or without the formation of vesicles, (2) dense perivascular dermal lymphohistiocytic infiltrate.

Treatment The patient is managed as in any acute dermatitis. As soon as the acute dermatitis has resolved, a suitable sunscreen is advised.

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