Also known as PLE, PME or PMLE, Polymorphic Light Eruption is the most common skin disorder characterized by photosensitivity and, after sunburn, is the most common sun-related problem seen by doctors.
PLE is a recurrent abnormal reaction to sunlight (or artificial ultraviolet radiation). It occurs after a delay on areas of the skin not regularly exposed, such as cleavage, upper arms, and trunk following sun exposure.
The disease can present in many forms (hence polymorphic), with variants including papular, vesicular, papulovesicular, plaque, erythema multiforme-like, insect bite-like, purpuric and sine eruptione.
Although PLE is regarded to be severely debilitating, there is a common understanding that only a fraction of patients present to dermatologists for treatment of their symptoms. The main reason for this is the lack of currently available efficacious therapies other than the administration of high doses of corticosteroids. PLE has a considerable impact on the quality of life for many people because of the need to avoid sun exposure during the spring and summer months.
PLE is very common world wide affecting up to 20% of southern Scandinavians and 5% of southern Australians. It has only rarely been reported in Asian and African countries. Its prevalence decreases with decreasing latitude.
The incidence of PLE has been reported in literature to be approximately 5% in Australia, 10% in the United States, 15% in the United Kingdom and approximately 15% – 20% in the most northerly latitudes of Europe. While it occurs in people with all skin types, it is more common in fair-skinned individuals.
A positive family history is common occurring in about a fifth of cases. 15% of monozygotic twins compared with 5 % of dizygotic twin pairs were both considered to have PLE, helping to confirm an inherited component to the pre-disposition to develop PLE.
PLE usually starts before the age of 30 and is much more common in females than males.
PLE eruption typically occurs after the first substantial UV radiation exposure and is common in spring and early summer. It has also been reported to occur after solarium use and, rarely, to visible radiation. Continued exposure often leads to abatement of symptoms – the ‘hardening phenomenon’, and so PLE is often less troublesome towards the end of summer than in spring.
Symptoms include non-scarring, itching (pruritis) or burning, red papules, vesicles or plaques and appears on sun-exposed skin 30 minutes to several hours following exposure to sunlight.
The eruption always occurs on an exposed, but typically not regularly exposed, site of the body and is intensely itchy, the itch sometimes preceding development of the rash. PLE outbreaks always tend to recur at the same site within an individual and are usually symmetrical. Symptoms usually resolve within a few days to 2 weeks of onset and with subsequent light avoidance.
PLE has many possible morphologic forms as suggested by the name (polymorphic). Papular and vesicular morphologies are most common, followed by plaque and papular subtypes. PLE often looks similar each time it occurs within an individual (monomorphic) however some patients do have different morphologies on different sites, for example plaques on the face and a papular eruption on the forearms.
PLE is believed to be a delayed hypersensitivity (allergic) reaction to an allergen produced in the body following sun light exposure. Individual susceptibility differs, and the delay of disease onset after exposure is usually several hours to days. There is, however, an early onset PLE variant with symptoms as soon as 30 minutes after first exposure.
The aetiology (origin) of PLE is unknown. It is believed to be a delayed type hypersensitivity response to an ultraviolet-induced allergen (photoallergen). The clinical observation that a first time eruption occurs after particularly intense ultraviolet exposure (deliberate sunbathing or solarium use) could indicate that such an exposure leads to the development of autosensitisation thus lending support to an autoimmune role in the development of this disease.
Differential diagnosis of Polymorphic Light Eruption include:
- Solar Urticaria (SU)
- Erthyropoietic Protoporphryria (EPP)
- photo-exacerbated dermatoses such as atopic or seborrheic eczema or acne
Sun avoidance and protective measures alone are sufficient for most mild/moderately affected people and are the mainstays of treatment in those severely affected. Avoiding unnecessary environmental exposure, such as beach holidays, wearing appropriate clothing with tightly woven fabrics, using broad spectrum high factor sunscreens applied thickly and frequently and avoiding the midday sun are some integral. For those more severely affected, the use of UV absorbing film, and shielding from glass, car and house windows is often appropriate.
Patients who experience PLE infrequently usually respond to short courses of oral corticosteroids. Topical steroids may also be useful. There is evidence for the use of topical steroids applied prophylactically immediately after exposure and this can also be helpful preventing flares during desensitisation.
Severe PLE treatment
For those more severely affected by PLE, prophylactic photochemotherapy with narrow-band UVB or PUVA given in spring serves to desensitise the skin and is beneficial in the majority of patients. Such therapy can in itself induce a reaction. Various other therapies have also been tried but appear largely ineffective. These include hydroxycholoroquinine, beta-carotene, nicotinamide, omega-3-polyunsaturated fatty acids. Oral immunosuppressive therapy with Azathioprine or Cyclosporin has been shown to be effective for severe cases.
A large number of PLE sufferers experience resolution of their symptoms or have a milder form of the disease seen a mean of 32 years after initial diagnosis. Whether this is due to spontaneous resolution or whether it is a result of repeated treatment courses is unknown.
- Hawk, J & Ferguson, J (2008). “Abnormal Repsonses to Ultraviolet Radiation: Idopathic, Probably Immunologic and Photoexacerbated”, in Fitzpatrick’s Dermatology in General Medicine 7th Edition. Ch 90, pp816-818.
- Ferguson, J, (2006). “Polymorphic light eruption”, in: Introduction to Photodermatology Photodynamic therapy and laser therapy, Ninewells Hospital and Medical School, Dundee.
- Hasan T, et al., (1998). “Disease associations in polymorphous light eruption. A long-term follow up study of 94 patients”, Archives of Dermatology Vol 134, pp1081-1085.
- Ferguson, J (1996). “The management of the photodermatoses with phototherapy” in Honigsmann H, Jori G, Young AR (eds) The fundamental bases of phototherapy. OEMF spa, Milan, Italy, pp 171-179.
- Gonzalez-Amaro R et al., (1991). “Immune sensitization against epidermal antigens in polymorphous light eruption”, Journal of American Academic Dermatology. Vol 24, pp70-73.
- Frain -Bell, W (1985). “The idiopathis dermatoses”, in Cutaneous photobiology. Oxford University Press, Oxford. pp24-59.