Spontaneously Resolving Pancreatic IgG4-Related Disease Representing With Systemic Involvement and Membranous Nephropathy.

Secondary membranous nephropathy (MN) is an increasingly recognized manifestation of immunoglobulin G4 (IgG4)-related disease (IgG4-RD). It is typically seen alongside tubulointerstitial nephritis but may occur independently. In this study, we discuss the case of a 65-year-old man who was initially investigated for steatorrhea and marked weight loss. He was diagnosed with idiopathic chronic pancreatitis, which spontaneously resolved with conservative management. He later represented with profound nephrotic syndrome, lymphadenopathy, and cutaneous lesions. There were no detectable antiphospholipase A2 receptor antibodies in the blood, but he was found to have elevated serum IgG4 levels. A kidney biopsy demonstrated antiphospholipase A2 receptor-negative MN with no evidence of tubulointerstitial inflammation. He was investigated for secondary causes of MN with a positron emission tomography-computed tomography scan, which showed increased uptake in the gastric mucosa and thoracic lymph nodes. An endobronchial lymph node biopsy showed reactive changes only; the diagnosis of multisystem IgG4-RD was made on a gastric biopsy, which detected marked polyclonal infiltration with IgG4+ plasma cells. He showed an excellent clinical and radiological response to induction therapy, with a tapering course of prednisolone followed by rituximab. This case adds to the limited body of evidence reporting MN without tubulointerstitial inflammation in the context of pancreatic IgG4-RD.