Immunoglobulin G4-related disease manifesting as a sino-orbital mass: a comprehensive case report and review of literature.

Background: Immunoglobulin G4-related disease (IgG4-RD) is a rare autoimmune fibroinflammatory condition that can affect multiple organs. Sinonasal and orbital involvement is exceedingly uncommon and poses significant diagnostic challenges. These manifestations often mimic malignancy, chronic infection, or other inflammatory disorders, leading to delayed diagnosis and repeated investigations. This study aims to illustrate the diagnostic challenges and management of IgG4-RD and to increase awareness of this rare presentation among clinicians. Case Description: We present a case of a 52-year-old male with a history of diabetes mellitus who developed a left-sided nasal mass extending into the orbit, resulting in nasal obstruction, epistaxis, proptosis, and diplopia. Imaging revealed a sinonasal mass with orbital extension through the lamina papyracea, raising suspicion for invasive or neoplastic pathology. Initial biopsies were inconclusive, demonstrating chronic inflammatory changes with no evidence of malignancy, granulomatous disease, or invasive fungal infection. Despite surgical debulking and close follow-up, symptoms persisted and recurred. Multiple subsequent biopsies were performed, which continued to show non-specific inflammatory findings. Further evaluation revealed elevated serum IgG4 levels, and repeat histopathological analysis demonstrated dense lymphoplasmacytic infiltration with an increased number of IgG4-positive plasma cells and an elevated IgG4/IgG ratio, consistent with IgG4-related disease. Correlation of clinical features, radiologic findings, laboratory results, and histopathology confirmed the diagnosis of IgG4-RD involving the sinonasal cavity and orbit. Conclusions: This case emphasizes the importance of maintaining a high index of suspicion for IgG4-RD in patients presenting with sino-nasal-orbital masses, considering the disease's rarity and non-specific initial symptoms. Early diagnosis through repeated tissue sampling and comprehensive evaluation is essential to avoid misdiagnosis and unnecessary interventions.