Case Report: IgG4-RD-related autoimmune pancreatitis combined with monoclonal gammopathy of undetermined significance.

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated chronic fibrotic inflammatory disorder. The coexistence of IgG4-RD with monoclonal gammopathy of undetermined significance (MGUS) is relatively rare, with only a few cases reported in the literature. This article reports a case of a 79-year-old male patient with clinical manifestations of persistent upper abdominal pain of unknown cause and recurrent pleural effusion. Auxiliary examinations indicated positive serum antinuclear antibodies and persistently positive IgG4; three-dimensional imaging reconstruction showed mild pancreatic swelling and the peripancreatic fat planes appeared blurred, which was consistent with the manifestations of pancreatitis. According to the "International Consensus Diagnostic Criteria for Autoimmune Pancreatitis (AIP)"of the diagnostic criteria of the International Pancreatic Disease Association, the patient was diagnosed with IgG4-RD AIP. At the same time, the patient's serum protein electrophoresis M protein was 2.34 g/L, and immunofixation electrophoresis confirmed it to be IgG-λ-type M protein. Combined with bone marrow smear and biopsy results, it was diagnosed as having MGUS. To our knowledge, this represents a rare case of IgG4-RD AIP concomitant with MGUS, and we provide an in-depth discussion of its clinical management and potential pathogenic association.