Antithyroid drug-associated MPO-ANCA-positive tubulointerstitial nephritis in a type 2 diabetes patient: a case report

A 54-year-old man diagnosed with type 2 diabetes and hyperthyroidism was prescribed propylthiouracil (PTU) after the patient developed hepatic dysfunction on thiamazole. At 50 mg/day of PTU, he was stable with thyroid-stimulating hormone receptor and thyrotropic antibody titers remaining stable. After four years of taking PTU, he was referred to the Department of Nephrology due to a rapid increase in his serum creatinine (Cr) level. He showed impaired renal function (Cr 2.26 mg/dL; estimated glomerular filtration rate (eGFR), 25 mL/min). In addition, urinary β2-microglobulin (β2 MG) was increased to 71,980 μg/L and was positive for myeloperoxidase (MPO)-anti-neutrophil cytoplasmic antibody (ANCA) (33.9 U/mL). Gallium scintigraphy demonstrated a remarkable accumulation in both kidneys. The patient was diagnosed with tubulointerstitial nephritis based on a renal biopsy, the results of which suggested that it might have been induced by PTU. He was treated with prednisolone (PSL) at 30 mg/day. As a result, within two weeks, Cr, eGFR, and urinary β2 MG levels were progressively improved to 1.72 mg/dL, 34 mL/min, and 22,020 μg/L, respectively. Therefore, we tapered off the PSL with a dose of 5 mg/day after approximately one year. There have been no exacerbated renal function parameters. Although there are many reports on patients developing MPO-ANCA-positive crescentic glomerulonephritis after the administration of PTU, we report on a relatively rare case in which interstitial nephritis occurred after the administration of PTU.