FRI531 IgG4 Related Mass -forming Thyroid Disease: Two Case Reports

Disclosure: R.S. Braham: None. C. Droumaguet: None. M. Vitellius: None. J. Tran-van-nhieu: None. E. Béquignon: None. P. Desgranges: None. N. Limal: None. M. Mahevas: None. B. Godeau: None. IgG4 thyroiditis is an invasive fibrotic process involving the thyroid in a systemic disease. It is a rare inflammatory autoimmune disease with insidious presentation and nonspecific symptoms.We describe two unusual cases of mass forming IgG4 thyroiditis that were diagnosed recently in our department. The first case is about a 42-year-old woman who has a history of Hashimoto thyroiditis with hypothyroidism presenting with a rapid goiter growth, neck pain, dysphagia and hoarseness. A lymphoma was suspected. Ultrasonography shows heterogeneous hypoechoic lesions that may infiltrate the perithyroid muscles. Fine-needle aspiration (FNA) was suspicious of IgG4 infiltrative disease which was confirmed by microbiopsy. Only the thyroid was hypermetabolic on fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) Scan. No improvement under corticosteroid treatment and Rituximab. Surgery was planified to relieve pressure symptoms. The thyroid surgery was very difficult because of the extensive fibrosis and only a biopsy was performed, confirming the diagnosis and excluding malignancy. The second case is about a 68-year-old woman with a history of hypertension and Graves disease presented with a neck right mass that was suspected to be a paraganglioma, hypermetabolic on FDG PET scan with no other localisation. This mass was surrounding the right primitive carotid artery, associated with thrombi of the internal jugular vein. FNA and microbiopsy found a fibrotic non specific tissue. Thyroidectomy and surgical biopsy of the neck mass were performed with histopathology confirming IgG4 disease on the thyroid gland with fibrosis. There were no hypocalcemia in the two cases and no other localisation. IgG4 related mass-forming thyroiditis is an extremely rare disease. It is now a recognizable pattern of IgG4 thyroiditis, and has as differential diagnosis Hashimoto’s thyroiditis, Graves disease and thyroidal carcinoma.We will discuss through these cases the different clinical presentation of this rare disease, the diagnostic tools, the treatment and the long term follow up. Presentation: Friday, June 16, 2023