Unilateral orbital mass as the initial presentation of pediatric antineutrophil cytoplasmic antibody associated vasculitis: eosinophilic granulomatosis with polyangiitis versus granulomatosis with polyangiitis

BACKGROUND: Eosinophilic granulomatosis with polyangiitis (EGPA), formerly known as Churg-Strauss syndrome, is a rare antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis characterized by asthma, eosinophilia, and systemic vasculitis. Ocular involvement is uncommon (6-20%) and usually follows systemic disease. In contrast, granulomatosis with polyangiitis (GPA) more frequently (30-60%) involves the orbit and may present as isolated orbital disease. Distinguishing EGPA from GPA can therefore be challenging when orbital inflammation is the initial manifestation, particularly in children. CASE PRESENTATION: A 7-year-old girl was referred with unilateral orbital swelling that was initially treated as preseptal cellulitis with oral amoxicillin and topical ciprofloxacin, without clinical improvement. Examination revealed a firm, mobile, tender superotemporal orbital mass with restricted upgaze, while visual acuity and fundus examination were normal. Orbital magnetic resonance imaging demonstrated an extraconal lesion exerting mass effect on the superior rectus muscle, globe, and lacrimal gland. The lesion was isointense on T1-weighted images, hyperintense on T2-weighted images, and showed marked contrast enhancement without diffusion restriction. Orbital biopsy revealed dense eosinophilic infiltration with granuloma formation and perivascular inflammation. Serologic testing demonstrated positive perinuclear (P-) ANCA with elevated myeloperoxidase (MPO) antibodies, supporting a diagnosis within the spectrum of ANCA-associated vasculitis. Systemic evaluation revealed no other inflammatory lesions, apart from bilateral otitis media with effusion. The patient underwent surgical debulking, which relieved the mass effect and provided diagnostic tissue. Subsequent treatment with high-dose systemic corticosteroids and rituximab resulted in clinical improvement with sustained systemic clinical and biochemical remission. Follow-up MRI, however, showed no significant reduction in the size of the orbital mass, necessitating a second, more extensive surgical debulking. CONCLUSION: Isolated orbital inflammation may represent an initial manifestation of ANCA-associated vasculitis in pediatric patients. Although eosinophil-rich granulomatous inflammation and MPO-ANCA positivity may suggest eosinophilic granulomatosis with polyangiitis, predominant orbital and ENT involvement in the absence of asthma or other atopic features may be more consistent with localized granulomatosis with polyangiitis. This case underscores the importance of early orbital biopsy, comprehensive serological evaluation, and cautious interpretation of residual orbital lesions within a multidisciplinary, longitudinal diagnostic approach.