BACKGROUND: Thyroid eye disease (TED) and IgG4-related orbital disease are distinct inflammatory conditions that rarely occur simultaneously. Their coexistence can pose diagnostic and therapeutic challenges, particularly in patients with systemic comorbidities. This report describes a rare case of concurrent TED and IgG4-related orbital disease in a patient with diabetes mellitus and details the surgical approach and postoperative results.

CASE REPORT: A 72-year-old man with a history of TED and diabetes had been experiencing progressive proptosis and orbital swelling for approximately 17 years. Despite consulting several doctors, he was refused surgery due to the associated high risks. He had facial changes, exophthalmos, and dry eyes, which led him to visit our clinic. Clinical evaluation and orbital imaging revealed changes consistent with TED, along with a localized orbital tumor extending into the deep orbital region. To alleviate the proptosis, we first performed an orbital tumor resection, along with orbital fat and bone decompression surgery. Five months later, we conducted an additional surgical resection of the residual right superior orbital tumor. Histopathological examination and immunohistochemical staining of the resected tissue, together with serological findings, confirmed the diagnosis of IgG4-related orbital disease.

CONCLUSIONS: This case highlights the importance of considering multiple etiologies in patients with atypical or long-standing TED. While orbital decompression is commonly performed for TED-associated proptosis, the presence of a localized IgG4-related orbital lesion can require surgical excision. This report suggests that combined surgical management can be considered in selected cases.

Keywords: Case Reports, IgG4-Related Disease, Ophthalmology, Orbital Neoplasms, proptosis, Thyroid Eye Disease