IgG4-Related Disease Inflamatory Pseudotumor Affecting the Sternoclavicular Joint: A Clinical Challenge.

IgG4-related disease (IgG4-RD) is a rare, progressive, and immune-mediated fibroinflammatory disorder that primarily affects middle-aged men and is more prevalent in Asian populations. Although extensively studied, its pathophysiology remains incompletely understood. This case report describes a 44-year-old male presenting with multiple abscesses and progressive inflammatory symptoms, ultimately diagnosed with IgG4-RD with musculoskeletal involvement. Imaging and histopathological evaluation confirmed osteolytic lesions and significant IgG4-positive plasma cell infiltration. Soft tissue tumors in IgG4-RD are exceptionally rare, further emphasizing the uniqueness of this case. The patient showed clinical improvement with corticosteroid therapy. This case highlights the importance of considering IgG4-RD in the differential diagnosis of soft tissue and bone lesions and underscores the need for a multidisciplinary diagnostic approach.