Supplementary Material for: Propylthiouracil-induced antineutrophil cytoplasmic antibody-associated vasculitis with overlap IgA nephropathy: a case report

Background
The anti-thyroid medication propylthiouracil (PTU) is a recognised cause of drug-induced antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Pauci-immune crescentic glomerulonephritis is the characteristic feature of this condition on renal biopsy. We present a case of PTU-induced AAV with the unusual histological finding of overlap IgA nephropathy (IgAN) in a young female with treatment-resistant Graves’ disease.

Case report
A 26-year-old female presented with an acute kidney injury, macroscopic haematuria and proteinuria 14 months after starting PTU for Graves’ disease. She had a history of established thyroid eye disease and a previous severe adverse reaction to Carbimazole. Her autoantibodies were strongly positive for myeloperoxidase (MPO)-ANCA (199 U/mL). Renal biopsy demonstrated both necrotising crescentic glomerulonephritis and prominent (3+) mesangial deposition of IgA. She was treated with glucocorticoids and Rituximab with sustained improvement in her renal function but persisting mild proteinuria and microscopic haematuria. PTU was ceased following a dose of radioactive iodine (RAI). 12 months post RAI, her Graves’ orbitopathy remained stable and her thyroid function was gradually normalising.

Conclusion
This was a case of drug-induced AAV with histological features of overlap IgAN. We suggest that this patient had pre-existing subclinical IgAN and then developed AAV secondary to PTU. The management of her thyroid disease was complex given the PTU-induced vasculitis, previous reaction to Carbimazole, risks of a thyroidectomy on immunosuppression and possible worsening of her eye disease with RAI. The glucocorticoids and Rituximab prescribed for vasculitis may have prevented progression of her Graves’ orbitopathy after RAI.