A Case of Difficult to Diagnose and Treat IgG4-related Disease Presenting with Paranasal Sinus, Orbital, and Buccal Lesions

IgG4-related disease (IgG4-RD) may also involve the paranasal sinuses, although such cases are rare. In this article, we present a case of IgG4-RD in a 66-year-old man with recurrent paranasal sinus, orbital, and buccal lesions. The patient initially presented with buccal lesions and limited mouth opening two years previously, but did not meet the diagnostic criteria for IgG4-RD at that time. After he was initiated on prednisolone (PSL) treatment, the IgG4 levels increased to 179 mg/dL, but subsequently improved along with the lesions and symptoms. However, while the PSL dose was being tapered, the patient developed worsening of the mouth opening difficulty, ocular motility disorder, and new lesions in the paranasal sinuses and orbit. Rhinosinusitis was suspected and the patient was referred to our department. Conservative treatment with antibiotics and other agents was ineffective, prompting endoscopic sinus surgery for both diagnostic confirmation and lesion control. Postoperative histopathology confirmed IgG4-RD. Postoperatively, treatment with PSL and azathioprine led to temporary improvement, but relapse occurred during PSL tapering. Long-term remission was achieved with PSL and rituximab. This case suggests that IgG4-RD involving the paranasal sinuses may require aggressive management, including steroids and rituximab, due to potential bone destruction and invasion of the surrounding structures. There are limited reports of IgG4-RD with paranasal sinus involvement, particularly those with repeated recurrences, such as this case. Further studies are warranted to establish optimal management strategies.