IgG4-related disease involving facial, infraorbital, auriculotemporal and optic nerves: multinervous cranial involvement in an adult patient.

IgG4-related disease (IgG4-RD) is a rare fibroinflammatory condition that can mimic infectious or neoplastic diseases, leading to diagnostic challenges. We report a case of a man in his mid-40s presenting with rapidly progressive orbital symptoms initially diagnosed as orbital cellulitis. Despite appropriate surgical and medical management, the patient's condition worsened with multiple cranial nerve involvement.MRI revealed an infiltrative process with perineural extension involving the optic, infraorbital, facial and auriculotemporal nerves. Histopathological examination confirmed IgG4-RD, demonstrating dense lymphoplasmacytic infiltration, storiform fibrosis and numerous IgG4-positive plasma cells. Serum IgG4 levels were markedly elevated.The patient responded well to corticosteroid therapy with significant clinical and radiological improvement. This case highlights an unusual presentation of IgG4-RD masquerading as orbital cellulitis and emphasises the importance of reconsidering the diagnosis when the clinical course is atypical or discordant with an infectious process.Early recognition is crucial to avoid unnecessary surgical interventions and prevent irreversible neurological damage.