An Overlapping Case of IgG4-Related Disease and Systemic Lupus Erythematosus.

We are reporting a case of a 63-year-old Chinese female who presented to the rheumatology clinic with positive antinuclear antibody and unintentional weight loss along with lymphadenopathy. Further workup revealed eosinophilia, elevated anti-double stranded DNA, serum protein, and serum IgG4 (immunoglobulin G4). The patient was diagnosed with systemic lupus erythematosus. Due to the raised IgG4 level along with eosinophilia and diffuse lymphadenopathy, IgG4-related systemic disease was suspected. It was confirmed with IgG4 staining on lymph node biopsy. Our case is presenting the fact that systemic lupus erythematosus and IgG4-related disease can be present in the same patient with multiple overlapping features making accurate diagnosis challenging.