A case of IgG4-related kidney disease with predominantly unilateral renal atrophy.

A 73-year-old Japanese woman was diagnosed with type 1 autoimmune pancreatitis (AIP) without kidney lesions. She was treated with prednisolone (PSL) 30 mg/day, and her AIP symptoms promptly improved, after which the PSL dose was gradually tapered to 5 mg/day. Her renal function had remained normal (serum creatinine 0.7 mg/dL) until 1 year before the current admission without any imaging abnormalities in the kidney. However, during this past year her renal function gradually declined (serum creatinine 1.1 mg/dL). Follow-up computed tomography incidentally revealed unilateral renal atrophy, which rapidly progressed during the subsequent 10-month period without left kidney atrophy. A diagnosis of IgG4-RKD probably due to TIN was made, and we increased the dose of prednisolone to 30 mg/day. 1 month after administration, multiple low-density lesions on both kidneys were improved slightly but almost all lesions persisted as atrophic scars. Our case suggested that unilateral renal atrophy can develop in patients with IgG4-related tubulointerstitial nephritis without hydronephrosis caused by retroperitoneal fibrosis, and that monitoring the serum creatinine levels is not always sufficient, thereby highlighting the importance of regular imaging monitoring to detect newly developing kidney lesions.