Methimazole-Induced Pauci-Immune Glomerulonephritis and Anti-Phospholipid Syndrome: An Important Association to Be Aware of

While methimazole (MMI) is the first line treatment for hyperthyroidism, this medication is not devoid of adverse effects. In this article, we present a 70-year-old male who admitted the hospital with right lower extremity pain and rash. The patient was recently treated with MMI for hyperthyroidism. Imaging studies revealed bilateral renal and splenic infarcts along with thrombosis of popliteal artery. Laboratory data revealed hematuria and proteinuria with positive (MPO), anti-proteinase-3 (PR3) and anti-cardiolipin IgG antibodies. Renal biopsy revealed pauci-immune glomerulonephritis and features with anti-phospholipid antibody syndrome (APS). MMI was discontinued and the patient was treated successfully with steroid therapy and anti-coagulation with resolution of proteinuria, hematuria and normalization of laboratory parameters. While MMI-induced pauci-immune glomerulonephritis has been previously reported, its association with APS has never been described before. Our case demonstrates that this rare diagnosis can be treated by early withdrawal of MMI and initiation of steroids along with anticoagulation.