SUN-LB095 Hashimoto's and Riedel's Thyroiditis: A Case Report

Riedel's thyroiditis is a rare form of chronic thyroiditis, predominantly characterized by a fibrotic process associated with mononuclear cell inflammation that classically extends beyond the thyroid into the perithyroidal soft tissue. It can occur in association with Hashimoto's thyroiditis, with elevated serum antithyroid antibody concentrations and lymphocytic infiltration seen in thyroid FNA. We report a case of 53-year-old Caucasian female patient with a clinical history of slowly growing painless multinodular goiter. The patient was referred to the Endocrinology department where physical examination revealed a non-suspicious diffusely enlarged goiter. An ultrasound guided fine-needle aspiration biopsy of the dominant nodule (2 cm in size) was performed, and cytologic findings were suggestive of chronic inflammatory process, with intense lymphocytic infiltration. Hypothyroidism and elevated serum thyroid peroxidase antibody (692 U/mL) were detected in blood work-up and hormone replacement therapy ensued. The diagnosis of Hashimoto's thyroiditis was then established ant the patient was discharged to the general practitioner. Four years after this diagnosis the patient complained of severe flank and lower abdominal pain and returned to our hospital. Abdominal CT scan identified a retroperitoneal periaortic and periureteral mass causing ureteral obstruction and acute renal failure. Amongst other diagnostic tests concurrently excluding malignant or infectious disease, CT scan guided biopsy was performed and revealed retroperitoneal fibrosis with vasculitis and hyaline rings surrounding small retroperitoneal vessels and nerves. Serum IgG4 was negative and erythrocyte sedimentation rate was marginally elevated. Whole body CT scan confirmed mediastinal diffuse fibrosis. Cervical ultrasound showed heterogeneous hypoechoic lesions infiltrating perithyroid muscles and a thyroid biopsy showed dense, hyalinized fibrous tissue that contained few lymphocytes, plasma cells, and eosinophils and almost no thyroid follicles, confirming the diagnosis of Riedel’s thyroiditis. Phospho-calcium metabolism disorders were excluded. Empiric therapy with Tamoxifen 10 mg daily and glucocorticoids was initiated. One-year follow-up imaging indicated disease stabilization. This case portraits the diagnostic challenge of clearly differentiating Riedel’s and Hashimoto’s thyroiditis in the same patient, as the results of imaging, laboratory and cytology studies are often similar. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.