Learning Objective
Explain the major types of photodermatoses, their pathogenesis, clinical features, and diagnostic clues, including polymorphous light eruption, phototoxic dermatitis, and cutaneous lupus erythematosus.
Polymorphous Light Eruption (PMLE)
- Most common idiopathic photodermatosis
- Triggered by sun exposure
- Clinical lesions: pruritic erythematous macules, papules, plaques, or vesicles
- Pathology: dermal edema and inflammation
- Occurs hours to days after UV exposure
Phototoxic Dermatitis
- Represents a non–non-immune-mediated photoreaction
- Clinically appears as sunburn-like erythema and blistering
in sun-exposed areas - Triggered by certain drugs, including:
- Phenothiazines
- Furosemide
- Ciprofloxacin
Cutaneous Lupus Erythematosus
A form of autoimmune photosensitive dermatosis
Types:
- Acute: classic malar (“butterfly”) rash
- Subacute: photosensitive rash on the anterior chest, upper back, and upper extremities
- Chronic: discoid plaques, often localized above the neck
Diagnosis:
Direct immunofluorescence:
- Deposition of IgG and complement at the dermal–epidermal junction
- Diagnosis supported by:
- Autoantibody serology (ANA, anti-dsDNA, anti-Ro/La)
- Clinical correlation
