IgG4-Related Orbital Disease vs. Idiopathic Orbital Inflammation: Clinical Features, Therapy and Outcomes in a Central-European Retrospective Single-Center Cohort

<b>Objective:</b> IgG4-Related Orbital Disease (IgG4-ROD) is an incompletely understood differential of idiopathic orbital inflammatory syndrome (IOIS). Accurate separation guides therapy and prognosis. This retrospective study also profiles its clinical features, therapy needs, and compares them with IOIS. <b>Methodology:</b> Fifty-four patients were biopsied between January 2016 and December 2023, comprising 18 who were diagnosed with IgG4-ROD (4 definite, 14 probable) and 36 with IOIS. Mean follow-up was 21.7 ± 26.2 months for IgG4-ROD versus 7.5 ± 10.3 months for IOIS. <b>Results:</b> Patients with IgG4-ROD were older than those with IOIS (mean 61.8 vs. 49.9 years). Gender distribution was balanced. The lacrimal gland (66.7% vs. 61.6%; <i>p</i> = 0.690) and extra-ocular muscles (55.6% vs. 30.6%; <i>p</i> = 0.076) were frequently involved in both entities, whereas paranasal sinus infiltration was significantly associated with IgG4-ROD (<i>p</i> = 0.003). Common shared symptoms (<i>p</i> > 0.05) included eyelid swelling (83.3% vs. 86.1%), exophthalmos (50% vs. 36.1%), and motility restriction (22.2% vs. 25%). Relative afferent pupillary defect (<i>p</i> = 0.042), chemosis (<i>p</i> = 0.02), and systemic disease (<i>p</i> = 0.005) were more prevalent in IgG4-ROD. During ≥ 6-month follow-up (<i>n</i> = 7), only 28.6% of IgG4-ROD patients achieved sustained remission; Kaplan-Meier analysis yielded a mean time to first event of 926 days. Additional steroid-sparing therapy was required more often in IgG4-ROD than in IOIS (<i>p</i> = 0.002). <b>Conclusion:</b> IgG4-ROD and IOIS share clinical features but differ in key aspects such as associated diseases, therapy requirements, and disease control. Understanding these differences is crucial for targeted diagnostics and individualized treatment strategies.