Immunoglobulin G4-related Disease with Multiple Organs Involvement Depicted on FDG PET/CT: A Case Report and Literature Review.

Introduction: Immunoglobulin G4-related disease (IgG4-RD) is a relatively rare immune-mediated chronic inflammatory disease with fibrosis newly defined in recent years. It can involve multiple systems and organs with complex clinical manifestations. Due to mass-like lesions, it is easily misdiagnosed as tumors.

Case Report: Herein, we report a 57-year-old woman treated for submandibular mass and anosmia. The serum IgG4 level was increased. The biopsy of the submandibular gland indicated salivary gland tissue and hyperplasia of fibrous tissue and lymphoid tissue. Immunohistochemical examination showed a large number of IgG4-positive plasma cells. M protein was found in the patient's serum by immunofixation electrophoresis, and plasma cell diseases were excluded by bone marrow puncture. PET/CT examination showed that besides the submandibular glands, the parotid gland, common bile duct, the transitional part of the left renal pelvis and ureter, retroperitoneum in the lower abdomen, and multiple lymph nodes were also involved. The patient was diagnosed with IgG4-RD, and after treatment with glucocorticoid, the enlargement of submandibular glands and decreased olfactory function improved. After 14 weeks of treatment, the serological examinations, PET/CT, and ultrasound re-examination results showed significant improvement. So far, the patient has been followed up for 27 months and is in continuous remission.

Conclusion: This case report aims to raise awareness of IgG4-RD and explore the value of PET/CT in the diagnosis and efficacy monitoring of the disease.