Purpose To investigate the clinical characteristics of idiopathic orbital inflammatory (IOI) disease with infraorbital nerve (ION) enlargement.

Design Retrospective, comparative case series.

Methods Participants: Consecutive patients who were diagnosed with IOI between January 2009 and December 2013 were identified. The study included patients whose medical and radiological data at diagnosis were available and whose follow-up period was more than 12 months after treatment. The patients were divided into two groups according to accompaniment of ION enlargement and were compared. Main outcome measures: clinical manifestation, radiology and treatment outcome.

Results Among 89 patients with IOI, 12 (13.5%) were identified to have ION enlargement. The ION-enlarged group showed a higher percentage of the patients with diffuse inflammation (66.7%, p<0.001). 91.7% of the ION-enlarged group showed inferiorly located inflammation. Patients with ION enlargement showed a significantly higher incidence rate of proptosis (p=0.013), pain (p=0.004) and altered sensation (p<0.001). The recurrence rate was significantly higher in the ION-enlarged group (83.3%) than in the other group (33.8%) (p=0.001). Repetitive inflammation (recurrence ≥3) with steroid dependency was found only in 19.5% patients without ION enlargement but in 66.7% patients with ION enlargement.

Conclusions Patients with ION-enlarged IOI showed distinct clinical and radiological characteristics. As IOI accompanied by ION enlargement showed significantly higher steroid dependency and recurrence rate, a more careful follow-up of patients during steroid tapering might be helpful to prevent recurrence of IOI.