Polymorphous light eruption (PMLE)

Polymorphous light eruption (PMLE) is a common sunlight-induced skin eruption that occurs most often in temperate climates. The onset occurs minutes to hours following sunlight or ultraviolet radiation (UVR) exposure. The amount of exposure typically varies from a few minutes to several hours, and is usually less than the minimal erythema dose (MED), which is that required for sunburn. The rash is pruritic and appears as erythematous papules, vesicles, or plaques on areas of exposed skin; it is typically patchy. The tendency to have an eruption is greatest in early spring and summer; lesions usually resolve as summer progresses and disappear by winter (however, attacks can occur during winter from sunlight reflected off of snow.) The reaction is thought to be a form of delayed-type hypersensitivity to photo-induced antigens.

There is a hereditary variant of PMLE (actinic prurigo) that occurs in people of Native American descent. It is usually more severe, has an early onset than the classic variant, and is more likely to persist into adulthood. Cheilitis and conjunctivitis are more common with this variant.

With what can polymorphous light eruption be confused?

PMLE must be distinguished from other light-induced dermatoses, such as porphyria and systemic lupus erythematosus. Blood, urine and stool should be evaluated for porphyrins, and antinuclear, anti-Ro and anti-La antibodies should be sought. Other photodermatoses should be considered, such as solar urticaria, which is brief (1-2 hours) and exhibits different lesional morphology. Sunlight-induced exacerbations of seborrheic dermatitis and atopic dermatitis, though typically eczematous, should also be considered. Pathology may be helpful (but is not usually diagnostic) in questionable cases.

How is polymorphous light eruption diagnosed?

A typical pattern of eruption on sun-exposed skin and a patchy pruritic rash are suggestive. Commonly affected areas are the upper cheeks, outer aspects of arms, shins, dorsal aspects of hands and feet, upper chest, and side and lower aspects of the neck. Pathology may sometimes be helpful, but it is not usually diagnostic. See “With what can it be confused?”

See: Pathology: Polymorphous Light Eruption

How is polymorphous light eruption treated?

Reduction or elimination of ultraviolet radiation exposure, broad spectrum high-SPF sunscreen, and protective clothing, including long-sleeved shirts and a wide-brimmed hat are helpful in mild cases. More severe cases respond, counterintuitively, to UVB phototherapy or PUVA, possibly through an immunosuppressive effect; 4-6 weeks of therapy are usually necessary. A high potency topical steroid can be effective, as well as a short course of oral steroid. Other proposed treatments of questionable efficacy are antimalarial medications and beta carotene. Immunosuppressive agents, such as azathioprine and cyclosporine, may be warranted in severe disease resistant to other treatments.

What is the prognosis for polymorphous light eruption?

The eruption usually lasts for one to several days, and sometimes weeks. The likelihood of developing the condition decreases over the course of the summer.

Date created 04/07/2007

Last updated 01/03/2009