Systemic immunoglobulin G4 (IgG4) disease and idiopathic orbital inflammation; removing 'idiopathic' from the nomenclature?

The discovery of systemic disease related to raised tissue and serum immunoglobulin G4 (IgG4) is changing diagnostic and therapeutic practice in many medical specialties. Orbital inflammation remains a diverse and heterogeneous group of disorders that can pose a diagnostic and therapeutic challenge, but with improved understanding and corresponding diagnostic advances the previously expansive group of idiopathies is reducing. The recent discovery that IgG4 has a causative role in a subtype of, what is currently termed, idiopathic orbital inflammation is encouraging. The term 'idiopathic' can now be removed from the nomenclature for another subtype of orbital inflammation. IgG4 disease should be especially considered in patients with a bilateral dacryoadenitis and systemic features (eg, lung and gastrointestinal involvement). However, reports are emerging suggesting that IgG4 may be responsible for more diverse disease subtypes. The relationship between IgG4-related disease and lymphoma remains unknown but vigilance is required.