A case report highlighting the diagnostic modalities for orbital IgG4 -related disease with systemic involvement.

IgG4-related disease ( IgG4-RD ) is an immune-mediated fibroinflammatory condition with varied clinical manifestations. This case highlights a case of ocular IgG4-RD with systemic involvement. A 41-year-old male patient presented with a painless bulging of the right eye over a 2-year period. Upon examination, there was axial proptosis with mild restriction in ocular motility during right lateral gaze. Investigation revealed elevated serum IgG4 levels. Contrast enhanced computed tomography (CECT) showed a well-defined, homogeneously enhancing mass lesion in the right orbit's intraconal space. Magnetic resonance angiography (MRI) showed hyperintense lesion of size measuring approx. 42 × 12 × 26 mm. An ultrasound (USG) guided orbital biopsy revealed lymphoproliferative lesions and abundant IgG4 + plasma cells with fibrosis. A fluorodeoxyglucose positive emission tomography (FDG-PET) scan showed a mildly enhancing soft tissue lesion in the right intraconal space. It also revealed abnormal metabolic activity in facial glands, pancreas, and mesenteric lymph nodes (SUV max 2.2).