An Atypical Cystic Renal Mass in a Patient with IgG4-Related Kidney Disease

We herein report a case of IgG4-related kidney disease (IgG4-RKD) with an atypical cystic renal mass in a 73-year-old man. Computed tomography revealed diffuse renal enlargement and a cystic mass in the left kidney. Blood tests revealed elevated IgG and IgG4 levels. A renal biopsy led to the IgG4-RKD diagnosis. The cystic mass was deemed to be benign based on the clinical, imaging, and ultrasonography findings. No malignancy or abscess formation was noted. Both the renal function and IgG4 levels improved after steroid treatment; moreover, the mass shrunk, suggesting an IgG4-RKD etiology. Cystic renal masses with capsule formation should be considered in patients presenting with IgG4-RKD.