A case of PLA2R-positive membranous nephropathy with subsequent development of IgG4-related disease.

Membranous nephropathy (MN) is a common cause of adult-onset nephrotic syndrome. It is also known as a minor but established renal manifestation of Immunoglobulin G4-related disease (IgG4-RD). Previous reports suggest that MN can also be an initial manifestation of IgG4-RD, all of which are phospholipase A2 receptor (PLA2R)-negative MN. We describe a case of PLA2R-positive MN that subsequently developed other manifestations of IgG4-RD. A 60-year-old male with nephrotic syndrome was diagnosed as primary MN with positive staining for PLA2R on the initial renal biopsy, which remained in partial remission with supportive therapy using angiotensin II receptor blocker (ARB) without steroid. About 1 year later, a renal mass was detected during an annual checkup, and contrast-enhanced computed tomography revealed low-density masses in bilateral kidneys and the head of the pancreas. The findings of endoscopic biopsy of the pancreatic mass were consistent with autoimmune pancreatitis (AIP) and the second renal biopsy showed the findings of MN with tubulointerstitial nephritis, both of which led to a diagnosis of IgG4-RD. The second renal biopsy also showed positive PLA2R. The patient received oral glucocorticoid therapy for IgG4-RD, which improved IgG4-related AIP and renal masses and also resulted in complete remission of MN. To our knowledge, this is the first reported case of PLA2R-positive MN with subsequent development of IgG4-RD. It is sometimes difficult to determine whether PLA2R-positive MN occurring with IgG4-RD is primary MN or secondary MN associated with IgG4-RD. The possibility of developing IgG4-RD should be considered even when preceding MN is PLA2R-positive, suggesting of primary MN.