Endocrine Abstracts

Background: We present a 47-year-old female, who is known to have recurrent Graves’ disease, developed vasculitic skin lesions upon treatment with propylthiouracil (PTU).

Case details: She was diagnosed with Graves’ disease in 2020 and was started on propylthiouracil as she could not tolerate carbimazole. Propylthiouracil was stopped after 18 months. Her thyrotoxicosis recurred after 6 months. Two months after propylthiouracil was restarted, she developed a new onset rash on her face followed by necrotic skin lesions on the back of her legs and her back. The rash was not worsened with sun light exposure. She did not recall any intercurrent illness or use of any other new medication. The clinical examination was unremarkable apart from fever and the skin lesions. There was no evidence of mucosal involvement. Her blood tests revealed positive anti-neutrophil cytoplasm (ANCA) antibodies: ANCA Myeloperoxidase (MPO) Antibodies * 3.8 kU/l (0 - 3.4), ANCA Serine Proteinase 3 (PR3) Antibodies *21.0 kU/l (0 - 1.9) while ANA and ENA antibodies were negative. Her computed tomography (CT) of chest, abdomen and pelvis was unremarkable apart from axillary lymph adenopathy. Her blood cultures showed no growth. A diagnosis of propylthiouracil-induced vasculitis was made by dermatologists. Propylthiouracil was discontinued and she was offered definitive treatment with either radioiodine or surgery. She was systemically well and her skin lesions showed signs of healing after drug withdrawal.

Conclusion: This case highlighted a rare though serious adverse effect of commonly prescribed antithyroid medications. Although one should exclude idiopathic vasculitis and vasculitis mimics in the first instance, propylthiouracil-induced vasculitis remains a possibility. Most patients respond to drug withdrawal or sometimes to immunosuppressants. Several studies reported the prevalence of PTU- induced vasculitis from 20% to 64%. Most patients have raised MPO-ANCA level while a small number have PR3-ANCA.