Plasma Cell-rich Nephritis with a Systemic Polyclonal Lymphoproliferative Disorder, Mimicking Idiopathic Multicentric Castleman Disease, Systemic Lupus Erythematosus, and IgG4-related Disease.

Idiopathic multicentric Castleman disease (iMCD), systemic lupus erythematosus (SLE), and IgG4-related disease (IgG4-RD) can cause lymphadenopathy with renal involvement. As no gold standards have been set for diagnosing these conditions, diagnoses can be made by excluding other conditions. However, some cases are difficult to identify. A 60-year-old man presented with lymphadenopathy, renal dysfunction, and hypocomplementemia. Autoimmune pancreatitis and iMCD had been suspected. A renal biopsy revealed immune complex-mediated glomerulonephritis superimposed on endothelial injury and plasma cell-rich tubulointerstitial nephritis with storiform-like fibrosis. While the features of iMCD, SLE, and IgG4-RD were present, a clear classification could not be achieved.