Methimazole-Induced ANCA Vasculitis: A Case Report.

Area of Science:

• Nephrology
• Rheumatology
• Internal Medicine

Background:

• Rapidly progressive glomerulonephritis (RPGN) is a clinical syndrome characterized by a rapid decline in kidney function.
• Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a significant cause of RPGN.
• Methimazole is a commonly used antithyroid medication for Graves' disease.

Observation:

• A 35-year-old woman presented with fatigue, weight loss, and alveolar hemorrhage.
• She had a 6-month history of methimazole treatment for Graves' disease.
• Clinical findings included respiratory failure, hypertension, and laboratory evidence of severe kidney injury (creatinine 2.65 mg/dL, eGFR 20 mL/min/1.73 m²), anemia, and positive ANCA (myeloperoxidase pattern).

Findings:

• Renal biopsy revealed crescentic pauci-immune glomerulonephritis with features of vasculitis.
• The patient was diagnosed with methimazole-induced ANCA-associated vasculitis.
• Treatment involved methimazole withdrawal, steroids, and cyclophosphamide.

Implications:

• This case highlights a rare but serious adverse effect of methimazole.
• Early recognition and management, including drug cessation and immunosuppression, are crucial for improving renal outcomes in ANCA-associated vasculitis.
• Long-term follow-up with azathioprine led to sustained renal function improvement and ANCA negativity.