IgG4-Related Disease: A Case Series Highlighting Diverse Clinical Manifestations and Treatment Outcomes.

IgG4-related disease (IgG4-RD) is a systemic immune-mediated fibroinflammatory condition characterized by tumor-like swelling of affected organs, lymphoplasmacytic infiltration enriched with IgG4-positive plasma cells, and variable degrees of fibrosis. We present three cases of IgG4-RD with diverse clinical presentations, highlighting the diagnostic challenges and management approaches. Our cases include a 45-year-old female with lacrimal and salivary gland involvement mimicking Sjögren's syndrome, a 77-year-old male with pancreatic mass, mesenteric vasculitis, and intra-abdominal lymphadenopathy initially suspected as pancreatic cancer, and a 75-year-old male with diffuse lymphadenopathy, initially thought to be lymphoma. All patients were successfully treated with rituximab with good clinical and radiological responses, emphasizing the importance of considering IgG4-RD in the differential diagnosis of conditions with multisystem involvement and atypical presentations.