Calciphylaxis — SCE Dermatology MCQ

Correct answer: C — Calciphylaxis

Calciphylaxis (C) is correct: it occurs in end-stage renal failure patients on haemodialysis with a raised calcium-phosphate product, and presents with exquisitely painful retiform purpura progressing to necrotic ulcers, classically on fatty areas such as the thighs and abdomen. The diagnostic histological hallmark is medial calcification of small to medium subcutaneous vessels with intimal proliferation and thrombotic occlusion, exactly as described in the biopsy here. In the UK, calciphylaxis (calcific uraemic arteriolopathy) occurs in around 1 in 600 people receiving dialysis, and management focuses on stopping precipitating drugs (warfarin, calcium-based phosphate binders, active vitamin D) and correcting the calcium-phosphate product. The combination of dialysis dependence, deranged mineral metabolism, and vascular calcification/thrombosis on biopsy is pathognomonic and excludes the other differentials. Why the other options are wrong: E. Warfarin skin necrosis: occurs typically within days of starting warfarin due to transient protein C deficiency, not in a chronic dialysis patient with a high calcium-phosphate product, and biopsy shows dermal vessel thrombosis without medial calcification. A. Pyoderma gangrenosum: produces undermined violaceous-edged ulcers, often with pathergy, but histology shows neutrophilic infiltration rather than vascular calcification and thrombosis. B. Leucocytoclastic vasculitis: biopsy shows neutrophilic infiltration of vessel walls with fibrinoid necrosis and no calcification, and lesions are typically palpable purpura rather than necrotic retiform ulcers. D. Cholesterol embolisation: follows vascular intervention or catheterisation and biopsy shows characteristic needle-shaped cholesterol clefts within vessel lumina, not calcific deposits. Key point: Painful retiform purpura in a dialysis patient with a high calcium-phosphate product and biopsy showing calcified, thrombosed small vessels in subcutaneous fat is diagnostic of calciphylaxis.

Reference: Kidney Care UK, Calciphylaxis (patient and clinical information), https://kidneycareuk.org/kidney-disease-information/kidney-conditions/calciphylaxis/