IgG4-related Orbital Disease Presenting as an Orbital Apex Lesion

IgG4-related disease is an uncommon multisystem inflammatory disease characterized by tissue infiltration by IgG4 plasma cells, extensive fibrosis, and sclerosing inflammation. Diffuse orbital involvement extending to the orbital apex and cavernous sinus has been reported, but a solitary well-circumscribed lesion at the apex has not been previously reported. Herein, we report a unique case of IgG4-related orbital disease presenting as a solitary well-circumscribed orbital apex lesion causing subacute visual decline in a 45-year-old male. MRI demonstrated bilateral lacrimal gland and infraorbital nerve enlargement and an 18 × 7 mm left orbital apex lesion demonstrating homogeneous contrast enhancement and isointense signal on T2. He was initially treated with tapering systemic corticosteroid therapy with improvement in his vision; however, he experienced visual deterioration 3 months later with recurrent inflammation. He subsequently commenced high-dose systemic corticosteroid therapy and rituximab infusions with improvement of left visual acuity to 6/7.5 + 2.