Aims The present study aimed to investigate the clinical implications of serum IgG₄ levels in patients with IgG₄-related ophthalmic disease (ROD).

Methods The medical records of 31 patients who met the diagnostic criteria for IgG₄-ROD were retrospectively reviewed. Twenty-five patients whose serum IgG₄ levels could be identified were included. Clinical manifestations and serum IgG₄ levels before and after corticosteroid treatment were obtained. Factors associated with relapse were evaluated by comparing the features of patients with disease relapse with those of patients without relapse.

Results Twenty-four patients were ‘definite’ and one was ‘probable’ for IgG₄-ROD according to the diagnostic criteria. Serum IgG₄ levels were higher in patients with systemic involvement (p=0.046). All patients improved clinically after corticosteroid treatment. Serum IgG₄ levels decreased after steroid treatment (p=0.005) and normalised in nine patients. In cases of relapse, serum IgG₄ levels increased along with the aggravation of symptoms (p=0.047). Serum IgG₄ levels that were still elevated (≥135 mg/dL) after steroid treatment (p=0.034) and cessation of steroid treatment during disease remission (p=0.043) were predictive factors for IgG₄-ROD relapse.

Conclusions Serum IgG₄ level can be considered an adjunctive marker for treatment response in IgG₄-ROD. Patients with serum IgG₄ levels that remain elevated after steroid treatment should be carefully observed for relapse. A continuing maintenance dose of oral steroid is recommended to prevent relapse, even when clinical remission is achieved.