P-82 Riedel's thyroiditis: three-year follow-up under steroid, rituximab and mycophenolate mofetil treatment
Authors: Akçay Seçkin , Apaydın Tuğçe , Yavuz Dilek 
Published: January 2024

Abstract

Introduction
Riedel's thyroiditis (RT) is an uncommon thyroiditis characterized by fibrosis, macrophage, and eosinophil infiltration and is assumed to be the primary cause of autoimmunity in the pathogenesis. Invasion of the surrounding tissues, particularly the trachea, occurs. RT is also regarded as thyroid involvement in IgG4-related systemic illness. Because there is no conventional medical treatment protocol for RT, this paper aims to highlight the problems we had in diagnosing and our approach throughout therapy.

Clinical Case
In the last 1.5 years, a 44-year-old female patient on levothyroxine replacement diagnosed with hypothyroidism developed bilateral swelling in the eyes, double vision, drooping eyelids, shortness of breath, and feeling something lodged in the throat. A diffusely enlarged and stiff thyroid gland was palpated in her physical examination. Neck CT revealed a diffusely enlarged thyroid gland 7cm in diameter and constricted trachea. She did not have any constitutional symptoms. According to physical and radiologic exams, preliminary differential diagnoses were anaplastic thyroid carcinoma and IgG4-related thyroiditis. In laboratory tests, TSH: 4.5 mIU/L, st3-4: normal, Anti TPO: +++ TRAB: 0.15 U/L, ANA: Negative, IgG4: 0.52 g/L (0.03-2.01), ACE:21.39. Since the thyroid fine needle aspiration biopsy reported a hypocellular smear, a lacrimal gland biopsy was performed for systemic involvement of IgG4 related disorder's. Her dyspnea was becoming critical; therefore, she was administered 0.5 mg/kg steroid for two weeks before the scheduled bilateral total thyroidectomy, and a considerable decrease in dyspnea, swallowing sensations, and regression in compression findings were seen. Lacrimal biopsies demonstrated persistent inflammation with plasma cells and severe fibrosis, consistent with late-stage IgG4-related illness. Both thyroid lobes were enlarged in neck T1 and T2-weighted MRI images (right lobe was 34×25×68 mm, the left lobe was 35×26×69 mm), diffuse hypointensity was noted, contrast uptake decreased in the thyroid parenchyma following IVCM, and the data was determined to be compatible with RT. The thyroid gland grew markedly on PET-CT, narrowing the air column, with increased FDG absorption in a heterogeneous character (SUVmax: 4.9), and mild-moderate involvement in bilateral lacrimal and parotid glands.The decision was made to continue steroid treatment at 1 mg/kg for one month. Rituximab was given twice every six months while the steroid was lowered. Mycophenolate mofetil (MMF) (2×500 mg) was introduced as a maintenance immunosuppressive medication. The initial radiologic findings regressed in the control neck MRI and PET-CT in the first year. The MRI findings were also steady in the second and third years of MMF.

Conclusion
Immunosupression therapy with steroid, rituximab and MMF was effective in our RT patient for the long term without significant complications. Clinical and radiological responses similar to surgery can be obtained with immunosuppressive agents.Figure 1.PET-CT and MRI images at diagnosis and third year