What is polymorphic light eruption (PMLE)?

From the Guidelines

Polymorphic light eruption is a skin condition that can be effectively managed with phototherapy, specifically psoralen-ultraviolet A (PUVA) therapy, which has been shown to provide a 65-100% photoprotection rate 1.

Key Characteristics of Polymorphic Light Eruption

• It is triggered by exposure to sunlight or artificial ultraviolet (UV) light.
• The condition appears as an itchy rash with small red bumps, blisters, or patches on sun-exposed areas of skin.
• Symptoms typically develop within hours to days after UV exposure and can worsen in spring and early summer.

Treatment and Prevention

• Treatment includes avoiding sun exposure, using broad-spectrum sunscreens (SPF 30+), and wearing protective clothing.
• In more severe cases, topical corticosteroids like hydrocortisone 1% cream can be used to reduce inflammation.
• For prevention, gradual, controlled sun exposure can help build tolerance, and some patients benefit from preventive treatments like low-dose UVB phototherapy before summer.

Phototherapy Options

• PUVA therapy is considered if UVB has failed, or has previously triggered the eruption sufficiently to compromise a course of therapy, or if there are other practical issues 1.
• The efficacy and safety of PUVA compared to ultraviolet B (UVB) have been studied, with one RCT not detecting any significant difference in efficacy between PUVA and NB-UVB 1.

Management Considerations

• The risk of provoking polymorphic light eruption is high, particularly with the first few PUVA exposures, and can be managed with potent topical steroid and subsequent lower dose increments 1.
• Post-treatment advice generally includes continued natural sunlight exposure, ranging from 2 h weekly to cautious exposure with sunscreens for extended outdoor stay.

From the Research

Definition and Characteristics of Polymorphic Light Eruption

• Polymorphic light eruption (PLE) is a highly prevalent photosensitivity disorder, estimated to affect 11-21% of people in temperate countries 2.
• It is typically characterized by nonscarring, pruritic, erythematous papules, plaques, or vesicles on sun-exposed skin that develop 30 minutes to several hours after sun exposure 3.
• The eruption may persist for a few hours to as long as 2 weeks 3.
• Females are affected two to three times more often than males 3.

Pathogenesis and Immunological Disturbances

• The pathogenesis of PLE has been difficult to define, although it appears to be an immune-mediated delayed-type hypersensitivity reaction 3.
• Abnormalities of arachidonic acid metabolism and a possible correlation with lupus are other theories that are reviewed 3.
• PLE is the most common immunologically mediated photodermatosis, demonstrating many abnormalities caused by critical failure of ultraviolet (UV)-induced immunosuppression 4.
• The unique expression of antimicrobial peptides in PLE, which is most likely determined by alteration of microbiome components upon UV exposure, implicates their possible triggering role and pathogenic significance in the eruption 4.

Clinical Presentation and Symptoms

• PLE is characterized by an intermittent eruption of non-scarring erythematous papules, vesicles or plaques that develop within hours of ultraviolet radiation exposure of patient skin 5.
• Together with the lesions, a terrible itch starts and increases with the spreading of the disease, sometimes aggravated by a sort of burning sensation 5.
• Clinical picture and symptoms can improve during the rest of the summer with further solar exposures 5.

Management and Treatment Options

• Treatment options for PLE include sun avoidance/sun protection, oral carotenoids, and antimalarials 3.
• Preventive treatment with broad-spectrum sunscreens and sunscreens containing DNA repair enzymes, as well as natural photohardening with graduate exposure to sunlight in early spring could be sufficient in milder cases 4.
• Antioxidants and topical calcipotriol are promising approaches for adjuvant prevention 4.
• Phototherapy, mainly with narrow band UVB rays, is more appropriate method in severe cases of the disease 4.
• The established treatment options for PLE include local and systemic glucocorticoids, systemic nonsedative antihistamines for itch relief, and rarely, immunosuppressive drugs in the refractory cases 4.