Diagnosis

Polymorphic light eruption

Etiology

Cause [dzu]

• Unknown, and it is likely to be multifactorial

Pathophysiology [fsc][dzu]

1. An unknown photoantigen is rendered immunogenic on exposure to UV

2. The antigen induced by UV radiation leads to a delayed hypersensitivity reaction

3. Pruritic erythematous papular/vesicular/nodular/plaques rash on sunlight exposed sites within hours to days of exposure

4. Subsides over the next 1-7 days without scarring

Classification of Photodermatoses: Skin diseases caused or exacerbated by solar radiation [p9b][y6g]

1. Immunologically mediated disease:

   Polymorphic light eruption, Juvenile spring eruption, Chronic actinic dermatitis, Actinic prurigo, Solar urticaria

2. Genophotodermatoses:

   Ataxia-telangiectasia, Bloom syndrome, Cockayne syndrome, Hailey–Hailey disease, Hartnup disease, Kindler syndrome, Rothmund–Thomson syndrome, Trichothiodystrophy, Xeroderma pigmentosum

3. Metabolic disease: cutaneous porphyria

4. Photoaggravated skin disease:

   Acne vulgaris, Atopic dermatitis, Bullous pemphigoid, Carcinoid syndrome, Cutaneous T-cell lymphoma, Darier’s disease, Dermatomyostitis, Disseminated superficial actinic porokeratosis, Erythema multiforme, Grover’s disease, Lichen planus, Lupus erythematosus, Pemphigus, Pityriasis rubra pilaris, Psoriasis, Reticular erythematous mucinosis, Rosacea, Seborrheic dermatitis, Viral infections

5. Drug- or chemical-induced photosensitivity:

   Photoallergy, Phototoxicity, Cutaneous porphyrias, Pellagra

Epidemiology

Prevalence per 100.000 [p9b][mza][y6g]

Approach

• Urine porphyrin

• Antibody levels: ANA, anti-SSA/Ro, anti-SSB/La

• Photopatch

• Phototesting with UV

• Biopsy

Treatment

1. Self-limited disease: rash usually goes away on its own within 10 days [41h]

2. Symptomatic treatment:

   • Itch: antihistamine, corticosteroid cream, cold compresses

   • Pain medication

3. Prophylaxis: [dzu]

   • Avoid sun exposure

   • Phototherapy (low-dose narrowband UV-B)

   • Sunscreen

Differential diagnoses

Acute intermittent porphyria, Drug eruptions, Eczema, Photosensitivity, Systemic lupus erythematosus, Urticaria