Eosinophilic Granulomatosis With Polyangiitis Presenting as Bilateral Orbital Inflammation.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a small vessel vasculitis that most commonly presents with peripheral eosinophilia, upper airway disease, and asthma, and can also cause cutaneous, cardiac, neurologic, musculoskeletal, gastrointestinal, and renal disease. This case describes a 57-year-old male with a history of chronic sinusitis and asthma who presented with bilateral orbital inflammation causing proptosis and diplopia. He was initially treated with antibiotics for orbital cellulitis without benefit, then high-dose prednisone with taper for idiopathic orbital inflammation, with resolution of ocular symptoms. He was diagnosed with EGPA after rheumatologic evaluation. Serum Immunoglobulin G4 (IgG4) level was significantly elevated, but his clinical presentation was more consistent with EGPA than IgG4-related disease (IgG4-RD). The patient significantly improved with the addition of mepolizumab and later methotrexate. This case details a rare manifestation of EGPA-bilateral orbital inflammation and highlights the potential overlapping features between EGPA and IgG4-RD.