Polymorphous light eruption (PMLE) is a term that describes a group of heterogeneous, idiopathic, acquired, acute recurrent photodermatoses characterized by delayed abnormal reactions to ultraviolet radiation (UVR) and manifested by varied lesions. The various morphologic types include erythematous macules, papules, plaques, and vesicles. However, in each patient the eruption is consistently monomorphous. By far the most frequent morphologic types are the papular and papulovesicular eruptions.
Causes of Polymorphous Light Eruption
A delayed-type hypersensitivity reaction to an antigen induced by UVR is possible because of the morphology of the lesions and the histologic pattern, which shows an infiltration of T cells. Immunologic studies thus far have not been rewarding except to suggest that a delayed-type hypersensitivity is the probable immunologic basis for PLE. More commonly, UVA is the action spectrum, but PLE lesions have been evoked with UVB and with both UVA and UVB.
Symptoms of Polymorphous Light Eruption
The rash usually consists of small red spots or blisters and can appear on any part of the body that has been exposed to sunshine, although commonly the face and the backs of the hands will be spared. It tends to heal without
Diagnosis
The diagnosis is not difficult: delayed onset of eruption, characteristic morphology, histopathologic changes that rule out lupus erythematosus, and the history of disappearance of the eruption in days. In plaque-type PMLE, a biopsy and immunofluorescence studies are mandatory to rule out lupus erythematosus. Phototesting is done with both UVB and UVA. Test sites are exposed daily, starting with 2 MEDs of UVB and UVA, respectively, for 1 week to 10 days, using increments of the UV dose. In 50% of patients; a PMLE-like eruption will occur in the test sites, confirming the diagnosis. This also helps to determine whether the action spectrum is UVB, UVA, or both.
Treatment
Prevention Sunblocks, even the potent UVAUVB sunscreens, are not always effective but should be tried first in every patient.
Systemic β-Carotene, 60 mg tid for 2 weeks before going in the sun and while in the Sun; this has not been very effective but can be tried before antimalarials. Antimalarials (hydroxychloroquine, 200 mg bid 1 day before and daily while on vacation or on weekends) are quite effective drugs for the treatment of PMLE in some patients and should be used in selected patients not helped by topical sunblocks or oral βcarotene.
PUVA Photochemotherapy This treatment given in early spring induces “tolerance” for the following summer. It is highly effective, but has to be performed before the sunny season or before taking a trip to a sunny region. PUVA treatments are given three times weekly for 4 weeks. It is not known whether their effectiveness is based on the production of an increase in the “filtering” capacity of the epidermis (increase in the stratum corneum and in melanin content of the epidermis) or to an effect of PUVA on T cells. PUVA treatments have to be repeated each spring but are usually not necessary for more than 3 or 4 years.
Narrow band UVB-311 nm has been used with success but there are not enough patients to make a comparison with PUVA. We have had both failures and successes with hydroxy-chloroquine and with prophylactic use of PUVA.
Prevention
It is not known how to prevent PMLE altogether. However, many people can avoid developing a rash by using effective sun protection during the middle hours of the day from September to May (Southern Hemisphere summer).
- Stay in the shade.
- Cover all affected areas with clothing.
References