RESUMEN
OBJECTIVE: IgG4-related disease (IgG4-RD) is a systemic mass-forming fibro-inflammatory condition which can affect nearly every organ system. Its pathophysiology remains incompletely understood, but affected tissues are characterized by a lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells which cause chronic inflammation, storiform fibrosis and phlebitis. These findings on histopathological specimens are considered the gold standard for the diagnosis. Clinical signs and symptoms largely depend upon organ involvement which can be singular or multiple, synchronous or metachronous. The organs most frequently involved are the pancreas (autoimmune pancreatitis (AIP), salivary and lacrimal glands (Mickulicz disease and sclerosing sialadenitis), biliary tree (sclerosing cholangitis or cholecystitis), retroperitoneum (retroperitoneal fibrosis), aorta (periaortic fibrosis), kidneys (interstitial nephritis) and thyroid (Riedel thyroiditis). Presentation is mostly subacute and general symptoms such as weight loss, asthenia or fever are moderate, but more prevalent in multi-organ disease. Lesions often mimic malignancy, but most respond well to steroid therapy. CONCLUSION: In this contribution we present a rare entity of IgG4-RD and discuss the utility of fluorine-18-fluorodeoxyglucose ((18)F-FDG) Positron emission tomography/computed tomography (PET/CT) in the diagnosis and treatment of this condition.