Photosensitive Eczemas

Photosensitive Eczemas - Sunny Skin Sorrows

• Photosensitive eczemas are abnormal, eczematous skin reactions triggered or worsened by sunlight exposure, primarily UV radiation.
• Action Spectrum: UVA (320-400nm, "Aging" rays), UVB (290-320nm, "Burning" rays), and occasionally Visible Light.
• Clinical features: Pruritic, erythematous papules, vesicles, or plaques on sun-exposed sites; sparing photoprotected areas (e.g., under chin, retroauricular).

⭐ PMLE (Polymorphic Light Eruption) is the most common idiopathic photodermatosis, characterized by delayed onset (hours to days) after sun exposure.

Photosensitive Eczemas - PMLE & CAD Spotlight

• Polymorphic Light Eruption (PMLE):

  • Most common idiopathic photodermatosis; delayed-type hypersensitivity to UV.
  • Onset: Hours-days post UV exposure (UVA > UVB).
  • Lesions: Itchy papules, plaques, vesicles on sun-exposed areas (often spares face, V-neck, arms).
  • "Hardening" phenomenon: Tolerance ↑ with repeated exposure.
  • Rx: Sun protection, topical steroids, short course oral steroids for severe cases.

• Chronic Actinic Dermatitis (CAD):

  • A.k.a. Actinic Reticuloid, Photosensitive Eczema, Persistent Light Reactivity.
  • Lesions: Severely itchy, thickened, lichenified plaques on chronically sun-exposed skin.
  • Often affects elderly men; may persist for years.
  • Broad action spectrum: UVB, UVA, and often visible light.
  • Rx: Strict photoprotection (broad-spectrum), potent topical/systemic steroids, immunosuppressants (e.g., azathioprine).

⭐ Chronic Actinic Dermatitis (CAD) often presents with persistent, lichenified eczema in sun-exposed areas, predominantly in elderly males, and may show a 'persistent light reaction'.

Photosensitive Eczemas - Drugs, Allergies Ahoy

• Abnormal reaction to UV radiation or visible light; eczematous changes.
• Key types: Phototoxic & Photoallergic.

• Phototoxic: More common; resembles exaggerated sunburn.
  • Drugs: Tetracyclines (esp. Doxycycline), NSAIDs, Amiodarone, Thiazides.
• Photoallergic: Less common; immune-mediated (Type IV).
  • Allergens: Sunscreens (PABA), fragrances, topical NSAIDs.

⭐ Photoallergic reactions are Type IV hypersensitivity, require prior sensitization, and can spread to non-exposed skin, unlike phototoxic reactions which are dose-dependent and confined to exposed areas.

• Solar Urticaria: Wheals on sun exposure; Type I hypersensitivity. Not eczematous. 📌 Remember Solar Urticaria = Sudden Urticaria.
• Actinic Prurigo: Familial, chronic, intensely itchy papules/nodules on sun-exposed skin; often starts in childhood.
• Chronic Actinic Dermatitis (CAD): Persistent eczema on sun-exposed sites, often in older men; can have ↓ MED (Minimal Erythema Dose).

Photosensitive Eczemas - Unmasking Sun's Mischief

• Eczematous reaction to UV/visible light on sun-exposed areas. Pruritus, erythema, papules, vesicles.
• Key Types:
  • Polymorphic Light Eruption (PMLE): Common; delayed onset.
  • Actinic Prurigo: Childhood; itchy nodules; HLA-DR4.
  • Chronic Actinic Dermatitis (CAD): Older men; lichenified; ↓MED.
  • Drug/Chemical-induced: Phototoxic/Photoallergic (drugs, chemicals).
• Key Approach:

⭐ Phototesting (including Minimal Erythema Dose - MED determination) and photopatch testing are key investigations to identify the causative wavelength and specific photosensitizer.

• Core Management: Strict photoprotection, topical corticosteroids/calcineurin inhibitors, systemic therapy (severe), hardening.

High‑Yield Points - ⚡ Biggest Takeaways

• PMLE: Most common; delayed itchy papules/plaques on sun-exposed areas.
• Spares photoprotected sites like under the chin and behind ears.
• Chronic Actinic Dermatitis (CAD): Persistent, lichenified eczema in older men; broad photosensitivity (UVA, UVB, visible light).
• Key symptom is intense pruritus; eruptions are typically symmetrical.
• Photopatch testing identifies photoallergens, differentiating from photoallergic contact dermatitis.
• Management: Strict sun protection, topical corticosteroids; phototherapy (hardening) for PMLE recurrence prevention.