Pseudoporphyria

Pseudoporphyria is a photodistributed bullous eruption that clinically and histologically resembles porphyria cutanea tarda, but with normal porphyrin levels.

• Drug induced: naproxen (especially in children with juvenile idiopathic arthritis), other NSAIDs (ibuprofen, ketoprofen, oxaprozin), diuretics (furosemide, bumetanide, hydrochlorothiazide), tetracyclines, fluoroquinolones, voriconazole, amiodarone, retinoids, dapsone, cyclosporine, and oral contraceptives.
• Non-drug: haemodialysis and chronic kidney disease (up to 10 to 18% of patients on dialysis), tanning bed use, and extensive sun exposure.
• Pathogenesis: UVA photosensitisation by phototoxic agents, with possible oxidative stress.

• Tense bullae, skin fragility, erosions, crusts, milia, and scars on sun exposed skin (dorsal hands and forearms, face, feet).
• Hypertrichosis and sclerodermoid change are usually absent.
• Naproxen induced pseudoporphyria presents with vesicles and scarring on the face and hands in children with arthritis.
• Itch is less prominent than in PCT; heals with scarring and dyspigmentation.

• Clinical and histological features indistinguishable from PCT: subepidermal blister, festooning, and thickened vessel walls.
• Normal plasma, urine, and faecal porphyrin levels (essential to exclude PCT and variegate porphyria).
• Drug exposure review and renal function evaluation; DIF may show IgG around vessels.
• Exclude bullous pemphigoid, epidermolysis bullosa acquisita, bullous lupus, and phototoxic drug reactions.

• Discontinue the offending drug; resolution usually takes weeks to 6 months.
• Strict photoprotection (UVA-blocking broad spectrum sunscreens, clothing, hats, avoid tanning beds).
• Local care: protect blisters, avoid trauma, topical antiseptics, and treat secondary infection.
• Dialysis related pseudoporphyria: optimise dialysis, use of N-acetylcysteine 600 to 1200 mg daily or oral vitamin C, and erythropoietin may help; exercise caution with iron therapy; consider conversion to high flux dialysis.
• Change NSAID class (use a drug not implicated, such as a short acting alternative) in children with arthritis.
• Review follow up for scarring and counsel on sun protection.