What is Polymorphic Light Eruption (PMLE)?

Polymorphic Light Eruption (PMLE)

Polymorphic Light Eruption (PMLE) is the most common immune-mediated photodermatosis characterized by recurrent, pruritic skin eruptions that develop on sun-exposed areas within hours to days after UV light exposure. 1

Clinical Presentation

PMLE manifests with several distinct morphological patterns:

• Skin lesions:

  • Erythema, papules, vesico-papules, occasionally blisters or plaques
  • Sometimes erythema multiforme-like lesions, insect bite-like wheals, or purpura 1
  • In dark-skinned individuals, particularly African Americans, a distinctive "pinpoint papular variant" with 1-2mm papules may occur 2
  • In Indian skin, unique pigmentary changes (both hypopigmented and hyperpigmented) are common 3

• Distribution:

  • Affects only sun-exposed areas
  • Common sites include V-area of chest, arms, forearms, legs, upper back
  • Face is less commonly affected 1
  • Spares flexural surfaces 2

• Timing and course:

  • Develops within hours to days after sun exposure
  • Symptoms last for a few days to about a week
  • Resolves without scarring 1

Epidemiology

• Prevalence: 10-20% of the general population 3
• Gender: Females affected 2-3 times more frequently than males 4
• Age: Most common between 20-30 years of age 3
• Skin type: Affects all races but more common in fair-skinned individuals (Fitzpatrick types I-IV) 4
• Most common photodermatosis in school-going children 3

Pathophysiology

PMLE is considered a delayed hypersensitivity response to newly UV-induced, but still unidentified, antigen(s). 1 The condition appears to have an immune-mediated basis, with evidence suggesting it may be a delayed-type hypersensitivity reaction. 4

Diagnosis

Diagnosis is based on:

1. Characteristic clinical history
2. Morphology of lesions
3. Phototesting results 1

Phototesting findings:

• Minimal erythema dose (MED) is typically normal
• Provocative phototests with UVA or UVB reproduce spontaneous lesions in approximately 50% of patients 1
• Some patients may show sensitivity to visible light 3

Histopathology shows:

• Hyperkeratosis and spongiosis with or without liquefactive degeneration in the epidermis
• Dense perivascular lymphocytic infiltrate in the upper and mid dermis 3
• Two common patterns:
  1. Focal lichenoid and perivascular lymphohistiocytic infiltrate with red blood cell extravasation
  2. Superficial and deep interstitial lymphocytic infiltrate with papillary dermal edema 2

Management

Prevention

• Sun protection:

  • Broad-spectrum sunscreens (covering both UVA and UVB)
  • Protective clothing
  • Sun avoidance during peak hours 1, 5

• Photohardening/Desensitization:

  • PUVA (psoralen plus UVA) or narrowband UVB therapy
  • Administered in early spring in temperate climates
  • Typically given 2-3 times weekly for 12-20 treatments 6
  • Most effective preventive approach 5
  • Risk of provoking PLE is high with initial exposures (12-50% of PUVA treatment courses) 6
  • Post-treatment advice includes continued natural sunlight exposure to maintain resistance 6

• Oral agents:

  • Antioxidants may be beneficial 1
  • Hydroxychloroquine 3
  • Oral carotenoids 4

Treatment of Acute Episodes

• Topical corticosteroids: First-line treatment for active lesions 1, 2, 3
• Systemic corticosteroids: For severe or extensive eruptions 1
• Antihistamines: Help control pruritus 2

Special Considerations

• Risk of provocation during phototherapy: PUVA or UVB therapy may initially provoke PMLE lesions

  • Can be managed with potent topical steroids and lower dose increments
  • Some clinicians administer oral prednisolone (40-50 mg) for the first 2 weeks of phototherapy to prevent provocation 6

• Timing of phototherapy: Important in temperate climates

  • If administered too early in the year, photoprotective effect may subside by mid-summer
  • If administered too late, the patient may have already suffered an eruption 6

• Long-term management: Annual desensitization with PUVA is not usually recommended due to the long-term risk of skin carcinogenesis 6

PMLE is a chronic condition that typically recurs annually but can be effectively managed with appropriate preventive measures and prompt treatment of acute episodes.