Investigators evaluated the efficacy, safety, and immunological effects of zanubrutinib monotherapy in patients with active lacrimal and submandibular gland Immunoglobulin G4 related disease. Secondary endpoints included metabolic imaging measures, clinical disease activity, serological biomarkers, and safety. At week 24, mean lacrimal gland volume decreased by 46.7% (p=0.008), while mean submandibular gland volume decreased by 29.9% (p=0.008). Total lesion glycolysis declined by 91.6 g (p=0.05) and total metabolic lesion volume decreased by 20.7 cm³ (p=0.05). Clinical disease activity also improved, with the IgG4-RD Responder Index falling by 6.0 points: (p=.01).