A 59‐year‐old woman with carbimazole‐refractory Graves disease presented with fever and extensive necrotising rash (Figure) 2 weeks after commencing propylthiouracil therapy. Investigations revealed undetectable thyroid‐stimulating hormone (< 0.004 mIU/L; reference interval [RI], 0.400–5.00 mIU/L), elevated levels of T3 (7 pmol/L; RI, 2.6–6 pmol/L) and T4 (22 pmol/L; RI, 9–19 pmol/L), raised C‐reactive protein (61 mg/L; RI, < 5 mg/L), and the presence of perinuclear antineutrophil cytoplasmic antibodies with elevated antiproteinase 3 antibodies. This was consistent with small vessel vasculitis and a persistent hyperthyroid state. Skin biopsy demonstrated leukocytoclastic vasculitis, a rare side effect of propylthiouracil therapy.1 A tapering course of prednisolone and mycophenolate was commenced. Areas of skin necrosis were managed with debridement and split‐skin grafting. Graves disease was treated with total thyroidectomy.
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