Renal lesions as the initial presentation of IgG4-related disease (IgG4-RD) and isolated IgG4-related kidney disease (IgG4-RKD) are rare.1,2

A 65-year-old male with a history of high-grade urothelial cell carcinoma in remission was found to have multiple renal lesions on surveillance imaging (Figure 1A). Urinalysis noted scant nondysmorphic hematuria without proteinuria. Serum creatinine was 1.05 mg/dL, estimated glomerular filtration rate 78 mL/min/1.73 m2, IgG 2430 mg/dL, and IgG4 1970 mg/dL (normal 2-121 mg/dL). Renal biopsy was negative for malignancy but demonstrated lymphoplasmacytic infiltrate with numerous polytypic plasma cells staining positive for IgG4 (Figures 1B,C). Comprehensive examination and imaging did not show any further organ involvement. The patient was treated with a glucocorticoid (GC) taper of 0.6 mg/kg over 8 weeks, resulting in a radiographic decrease in size of renal lesions and an IgG4 reduction to 653 mg/dL. Subsequent treatment with 2 doses of 1000-mg rituximab (RTX) separated by 2 weeks led to complete radiographic resolution of the renal lesions and IgG4 lowering to 366 mg/dL. Rituximab (1000 mg) was repeated 6 months later, with IgG4 levels decreasing to 214 mg/dL, at which point the patient elected ongoing laboratory surveillance every 6 months.

(A) CT urogram (coronal view) demonstrating multiple round hypodensities in bilateral kidneys. (B) Renal biopsy demonstrating numerous lymphocytes and plasma cells (H&E staining, 200×). (C) IgG4 staining from renal biopsy demonstrating > 10 IgG4 staining plasma cells per high-power field (200×). CT: computed tomography.

Although obliterative phlebitis and storiform fibrosis were absent on renal biopsy, obliterative phlebitis is not typically seen in IgG4-RKD, and a subset of patients with IgG4 tubulointerstitial nephritis show plasma cell-rich interstitial inflammation with minimal fibrosis.3 Delayed treatment of IgG4-RKD is associated with partial renal scarring on imaging.4 Although IgG4-RD is typically responsive to GCs, refractory cases demonstrate excellent response to RTX.5 Among patients achieving remission, a consensus on the appropriate treatment duration and monitoring off therapy has yet to be established.