ESSENTIALS OF DIAGNOSIS
Mainly affects men older than 50 years.
Lymphoplasmacytic infiltrates causing tumors or fibrosis in any organ or tissue.
Subacute onset; constitutional symptoms rare.
IgG4-related disease is a systemic disorder of unknown cause marked by highly characteristic fibroinflammation that contains IgG4 plasma cells and can infiltrate virtually any organ. Elevations of serum IgG4 levels occur often but are not diagnostic. The disorder chiefly affects men (75% of patients) over the age of 50 years.
IgG4-related disease can affect any organ of the body, can be localized or generalized, demonstrates the same distinctive histopathology at all sites of involvement, produces protean manifestations depending on location and extent of involvement, and causes disease that ranges in severity from asymptomatic to organ- or life-threatening. The inflammatory infiltration in IgG4-related disease frequently produces tumefactive masses that can be found during physical examination or on imaging. Some of the common presenting manifestations include enlargement of submandibular glands, proptosis from periorbital infiltration, retroperitoneal fibrosis, mediastinal fibrosis, inflammatory aortic aneurysm, and pancreatic mass with autoimmune pancreatitis. IgG4-related disease can also affect the thyroid (formerly Riedel thyroiditis), kidney, meninges, pituitary, sinuses, lung, prostate, breast, and bone. Most symptomatic patients with IgG4-related disease present subacutely; fever and constitutional symptoms are usually absent. Nearly half of the patients with IgG4-related disease also have allergic disorders such as sinusitis or asthma.
Serum IgG4 levels are usually, but not invariably, elevated so this finding cannot be used as the sole diagnostic criterion. The infiltrating lesions in IgG4-related disease often produce tumors or fibrotic changes that are evident on CT or MRI imaging. However, the cornerstone of diagnosis is histopathology. The key pathological findings are a dense lymphoplasmacytic infiltrate rich in IgG4 plasma cells, storiform (matted and irregularly whorled) fibrosis, and obliterative phlebitis.
IgG4-related disease can mimic many disorders including sarcoidosis, Sjögren syndrome (lacrimal gland enlargement), pancreatic cancer (pancreatic mass), chronic infections (eg, HIV, hepatitis C), and granulomatosis with polyangiitis (proptosis). Lymphoma can mimic some of the histopathologic features of IgG4-related disease.
Patients who are asymptomatic and have no organ-threatening disease can be monitored carefully. Spontaneous resolution can occur. Initial therapy is usually oral prednisone 0.6 mg/kg/day, tapered over weeks or months depending on response. Given that corticosteroid monotherapy may fail to control the disease and can cause significant long-term toxicity, immunosuppressants, especially rituximab, are often used. The degree of fibrosis in affected organs determines the patient’s responsiveness to treatment.