Photosensitivity disorders: cause, effect and management

Abnormal photosensitivity syndromes form a significant and common group of skin diseases. They include primary (idiopathic) photodermatoses such as polymorphic light eruption (PLE), chronic actinic dermatitis (CAD), actinic prurigo, hydroa vacciniforme and solar urticaria, in addition to drug- and chemical-induced photosensitivity and photo-exacerbated dermatoses. They can be extremely disabling and difficult to diagnose. PLE, characterized by a recurrent pruritic papulo-vesicular eruption of affected skin within hours of sun exposure, is best managed by restriction of ultraviolet radiation (UVR) exposure and the use of high sun protection factor (SPF) sunscreens. If these measures are insufficient, prophylactic phototherapy with PUVA, broadband UVB or narrowband UVB (TL-01) for several weeks during spring may be necessary. CAD manifests as a dermatitis of chronically sun-exposed skin. Again, UVR exposure needs to be restricted; cyclosporine, azathioprine or PUVA may also be necessary. Actinic prurigo is characterized by the presence of excoriated papules and nodules on the face and limbs, most prominent and numerous distally. Actinic prurigo is managed again by restriction of UVR and the use of high SPF sunscreens; PUVA or broadband UVB therapy, or low doses of thalidomide may be necessary. Hydroa vacciniforme causes crops of discrete erythematous macules, 2 to 3mm in size, that evolve into blisters within a couple of days of sun exposure. Treatment for this rare disease is difficult; absorbent sunscreens and restricted UVR exposure may help. Solar urticaria is characterized by acute erythema and urticarial wealing after exposure to UVR. Treatment options for solar urticaria include non-sedating antihistamines such as fexofenadine and cetirizine; other options include absorbent sunscreens, restriction of UVR at the relevant wavelength, maintenance of a non-responsive state with natural or artificial light exposure and plasmapheresis. Industrial, cosmetic and therapeutic agents can induce exogenous drug- or chemical-induced photosensitivity. The clinical pattern is highly varied, depending on the agent; treatment is based on removal of the photosensitizer along with restriction of UVR exposure. Predominantly non-photosensitive dermatoses may also be exacerbated or precipitated by UVR; exposure to UVR should be reduced and sunscreens should be advocated, along with appropriate treatment of the underlying disease.