Orbital Pseudotumor - A Rare Variant of Granulomatosis with Polyangiitis

Granulomatosis with Polyangiitis (GPA) is an autoimmune small vessel vasculitis with unknown aetiology, characterized by necrotizing granulomatous inflammation affecting the renal, pulmonary, upper airways and ocular systems and is often associated with circulating Anti-Neutrophil Cytoplasmic Antibodies (ANCA) against proteinase 3. Here we report a presentation of GPA showing orbital involvement (without systemic involvement) with the classical histological triad, and also significant localized tissue eosinophilia which corresponds with the rare eosinophilic form of GPA. This variant of GPA should be differentiated from Eosinophilic Granulomatosis with Polyangiitis (EGPA); and the differential diagnosis between the two entities, and also the treatment of GPA is discussed.