Polymorphous light eruption

Typically, the first episode develops in the spring following the first exposure to intense sun.[10] Further episodes of the irritable rash occur several hours to days following subsequent sun exposure.[11]

PLE appears on areas of the skin newly exposed to sunlight such as the visible part of the neckline, backs of hands, arms and legs, and feet, but less commonly the face.[2][6] At these areas, there may be feelings of burning[9] and severe itching. Smooth red-topped small papules which merge into plaques, small fluid-filled blisters (papulovesicles)[2] and less commonly target-shaped lesions which look like erythema multiforme may be visible.[5] In addition, it may occur in other parts of the body in some people treated for inflammatory skin diseases with phototherapy.[2]

The rash is usually quite symmetrical and characteristic for each individual, appearing similar with each recurrence, but can look dissimilar in different people.[10]

Fever, fatigue and headaches have been previously associated with the eruption, but are rare.[2]

The rash may persist for many days to a couple of weeks,[5] resolving spontaneously without scarring as long as further sunlight exposure is avoided.[2]

Recurring yearly, the eruption can sometimes last longer than a few days if persistent and repeated sun exposure occurs.[2] However, the "hardening" effect, with respite during the later summer, frequently occurs with gradual exposure of sunlight,[5] eventually leading to significant improvement.[2]

The cause of PLE is not yet understood, but several factors may be involved.[6] It is thought to be due to a type IV delayed-type hypersensitivity to an allergen produced in the body following sunlight exposure,[12] in a genetically susceptible person.[10] It is also thought that skin microbiome or microbial elements could be involved in pathogenesis of the disease [13][14]

The diagnosis of PLE is typically made by assessing the history and clinical observations. Any investigations are usually to exclude other conditions, particularly lupus and porphyria.[9]

Blood tests are usually normal. However, positive antinuclear antibody and extractable nuclear antigen (anti-Ro/La) in low titre may be found, even in the absence of other criteria to suggest a diagnosis of lupus erythematosus. If clinical findings suggest a possibility of porphyria, urinary and red cell porphyrin screening may be performed and are negative in PLE.[2]

Photoprovocation tests are usually not required but may be undertaken by specialised centres in winter.[2] When a decision to undertake this is made, a small area of the frequently affected skin is exposed to varying doses of UVA and minimal erythema dose (MED) (amount of UV radiation that will produce minimal redness of skin within a few hours following exposure)[2][17] of broadband UVB for three consecutive days. An examination of the skin to detect the rash is made, however, up to 40% have false negative responses.[2]

Management entails regulating triggers whilst simultaneously inducing "hardening"; that is, steadily increasing exposure to sunlight,[2] as light sensitivity is reduced with repeated sun exposure[15]

Covering up with densely woven clothing has also been shown to help, in addition to applying a broad-spectrum, water-resistant semi-opaque sun protection factor (SPF) 50+ sunblock cream before sun exposure and then every two hours thereafter confers some protection.[2]

The application of topical corticosteroids may lessen the redness and itch,[2] and for preventing predictable holiday flare-ups, short courses of oral corticosteroids are sometimes considered.[2]

Another treatment option is a supervised course of low dose phototherapy, usually undertaken in winter.[2] If resistant, the administration of hydroxychloroquine in early spring is sometimes considered.[10]

As sun exposure is avoided, vitamin D levels may fall and hence supplements are sometimes advised.[22]

Generally, PLE resolves without treatment; also, PLE irritations generally leave no scar.[15]

There may be a possible link with autoimmune thyroid disease.[9] Some progression to autoimmune disease has been observed.[23] However, another study of people with elevated titres of antinuclear antibodies with PLE found no progression to lupus erythematosus after an 8-year follow-up.[16]

In the United States, whilst one-quarter of people being investigated for a photosensitivity disorder were diagnosed with PLE, the prevalence in the general population is 10 to 15% and may even be as high as 40% as suggested in one study of more than 2000 people.[5][6] It is also particularly more prevalent in Central Europe and Scandinavia.[4]

PLE is more common in young adults and has a female preponderance[5] with a ratio of 2:1 female-to-male. In Germany the female to male ratio has been cited as 9:1.[4] It can, however, occur in all age groups and all skin types.[6]

Those experiencing sun exposure all year round seldom acquire PLE eruption.[15] Hence, it is less common near the equator.[16]

The cases of this condition are most common between the spring and autumn months in the northern hemisphere and at higher altitudes.[12]

Reports of psychological distress have been made in more than 40% of peoples with PLE.[16] This includes emotional distress, anxiety and depression[12]

Thomas Bateman, following on from findings of his predecessor, Robert Willan,[24] first recorded a description of PLE in the nineteenth century, defining it as eczema solare with recurrent non scarring eczematous lesions triggered by sun exposure.[25][26]

Danish physician Carl Rasch first described the eczema-like polymorphic light eruption in 1900, following his interest in the effect of sunlight on the skin. He has since been credited with coining the term "polymorphic light eruption".[27][28]

• Photosensitivity with HIV infection
• List of cutaneous conditions

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