IgG4-Related Disease: A Rare Case of Simultaneous Lung and Retroperitoneal Involvement.

Immunoglobin G4-related disease is a progressive immune-mediated fibroinflammatory condition that can affect any organ, causing a tumor-like swelling appearance. We present a case of a 57-year-old male who presented with a one-month history of weight loss, constant abdominal pain with dorsal irradiation, night sweats, and respiratory symptoms. CT scan revealed multiple mediastinal and retroperitoneal adenopathies, right pulmonary consolidation, and retroperitoneal fibrosis. Transthoracic pulmonary biopsy and excisional cervical lymph node biopsy revealed fibroinflammatory disease related to IgG4, with normal serum IgG4. The patient presented a good response to glucocorticoids, a clinical characteristic of this disease. The diagnosis of immunoglobin G4-related disease is challenging, due to the nonspecific clinical manifestations, requiring a high level of suspicion in order to perform the appropriate immunohistochemical examination.