Orbital Granulomatosis With Polyangiitis Mimicking IgG4-Related Disease in a 12-Year-Old Male.

Granulomatosis with polyangiitis is rare in children. We report a case of a 12-year-old male who presented with new symptoms of left eyelid swelling and ptosis. Magnetic resonance imaging showed an enhancing orbital mass suspicious for a neoplasm. Excisional biopsy was performed. Microscopic examination revealed fibrovascular tissue with dense collagenous fibrosis and mixed inflammatory infiltrate that included many plasma cells. Many small and medium-sized blood vessels showed granulomatous and necrotizing vasculitis with disruption of the vessel walls and fibrinoid necrosis. Immunostain for IgG highlighted the numerous plasma cells, approximately 50% of which were positive for IgG4 immunostain. A diagnosis of granulomatosis with polyangiitis was suggested, with recommendation of serologic testing for anti-neutrophil cytoplasmic antibodies. Serum anti-neutrophil cytoplasmic antibodies were borderline high with a cytoplasmic staining pattern. The patient improved with steroid and methotrexate therapy. Granulomatosis with polyangiitis can present as an orbital mass in up to 30% of children. It may be misdiagnosed as IgG4-related disease since the inflammatory background in both conditions may be rich in plasma cells with a high proportion of IgG4+ plasma cells, and accompanied by fibrosis and obliterated blood vessels. The differential diagnosis in this location should also include inflammatory pseudotumor and inflammatory myofibroblastic tumor. Knowledge of this unusual manifestation of granulomatosis with polyangiitis and its diagnostic pitfalls can facilitate early diagnosis and treatment.