Polymorphic light eruption

Published on 18/03/2015 by admin

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Last modified 18/03/2015

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Polymorphic light eruption

Warwick L. Morison and Elisabeth G. Richard

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Polymorphic light eruption is the most common photodermatosis with a prevalence of 10–20% in temperate climates, particularly among young women. It develops on sun exposed body parts hours to a day or more following specific exposure to sunlight, usually in spring or early summer. The morphology varies, with papular or papulovesicular forms being most common, and the rash is always pruritic. Plaques, insect-bite type, and erythema multiforme variants are much less common. In most patients the tendency to develop polymorphic light eruption diminishes with repeated exposures to sunlight, a phenomenon called hardening.

Management strategy

The treatment of polymorphic light eruption consists of two phases: treatment of established disease after the rash has appeared; and the prevention of the rash in patients known to have the disease. Application of a mid-potency or high-potency corticosteroid cream or ointment, two or three times daily, is usually sufficient to reduce symptoms and clear the rash in most patients with established disease. Use of topical corticosteroids as treatment is based on historical clinical experience rather than formal clinical studies. A few patients with extensive disease and marked symptoms require oral prednisone in a dose of 60–80 mg for a few days, followed by rapid reduction of the dose over a week.

Preventive management is the best choice for patients diagnosed with the disease. The majority of patients with polymorphic light eruption have high-threshold disease, so they require prolonged exposure to sunlight or artificial sources of ultraviolet (UV) radiation to trigger the reaction. Most of these individuals do not seek medical advice but learn to limit their exposure to levels below their threshold or, in some cases, to prevent the disease by use of sun screens. Patients seeking medical advice usually have low-threshold disease, often triggered by 15–30-minute exposures to sunlight, leading to marked limitation of outdoor activities.

The initial approach to the prevention of polymorphic light eruption is avoidance of exposure to sunlight using a combination of reduced time spent outdoors, restriction of exposure to early morning and late afternoon hours, wearing of protective clothing, and application of broadband sun screens that protect against both UVA and UVB wavelengths. This strategy is most likely to be effective in patients with high-threshold disease and those triggered by UVB radiation.

The most effective approach for patients with low-threshold disease is desensitization using a course of PUVA (psoralen–UVA), narrowband (311 nm) UVB phototherapy or broadband UVB phototherapy in spring, followed by regular exposures to sunlight during summer to maintain tolerance. Photo(chemo)therapy stimulates the hardening phenomenon and aims to induce photo-adaption. This approach is successful in preventing polymorphic light eruption in up to 90% of patients, but requires planning as treatment lasts for about a month. Patients who develop polymorphic light eruption while on treatment should continue therapy and may require topical or oral corticosteroids to control the rash.

Hydroxychloroquine, β-carotene, and nicotinamide are reported to provide moderate and safe protection in polymorphic light eruption and may be considered in patients unable to undertake, or who are unresponsive to, desensitization therapy. Hydroxychloroquine is sometimes a useful preventive measure during a brief winter vacation in a warm climate. It should be started 3 days before the vacation in a dose of 400 mg daily, and continued throughout the vacation.

Specific investigations

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