Limited granulomatosis with polyangiitis in children with idiopathic orbital inflammation: a case series and literature review.

Idiopathic orbital inflammation (IOI) is a diagnosis of exclusion, but the exclusion of other inflammatory diseases of the orbit is broad and relies on clinician experience, response to corticosteroid, or biopsy. This study aimed to investigate the presence of granulomatosis with polyangiitis (GPA) in patients initially diagnosed as IOI and describe its clinicopathological features, ANCA status, treatment, and outcome. We performed a retrospective case series study of children diagnosed with limited GPA (L-GPA) in patients with IOI. A systematic review of the literature was performed in children with GPA and orbital mass. Eleven of 13 (85%) patients with IOI had L-GPA. Two additional patients with orbital mass and L-GPA were included in this analysis. The median age was 10 years, and 75% were female. Twelve cases were ANCA positive and 77% were MPO-pANCA positive. Most patients had a poor response to treatment and had a high relapse rate. Based on literature review, 28 cases were found. Most (78.6%) were female with a median age of 9 years. Three patients were misdiagnosed as IOI. Patients with L-GPA more frequently had MPO-pANCA positivity (35%) than children with systemic GPA (18%) and were less often PR3-cANCA positive than patients with systemic GPA (18% vs. 46%). L-GPA accounts for a high prevalence of children diagnosed as IOI. The high prevalence of MPO-pANCA observed in our study may be related to L-GPA rather than with the orbital mass. Long-term follow-up, orbital biopsy, and serial ANCA testing are necessary to exclude GPA in patients with IOI.