Abstract #1385480: Goiter and Abdominal Mass: A Rare Presentation of Riedel’s Thyroiditis

Abstract

Riedel’s thyroiditis (RT), also known as fibrous thyroiditis, is a rare inflammatory autoimmune disease that is often associated with various forms of systemic fibrosis such as sclerosing mesenteritis (SM). A 38-year-old female with a past medical history of hypertension presented with a painful growing goiter and a mesenteric mass, which was complicated by biliary obstruction and hydronephrosis. Physical exam showed tenderness on the abdomen and a diffusely enlarged firm thyroid gland, with no palpable nodules. Initial labs revealed C-reactive protein of 115 mg/L, TSH 180 mIU/L; Free T4: 0.79 ng/dL, positive Thyroid Peroxidase (>1051 IU/mL); normal IgG1 and IgG4. CT abdomen/pelvis demonstrated a mesenteric mass that encased multiple mesenteric vessels and the right ureter without bowel obstruction. Thyroid ultrasound showed an enlarged heterogeneous thyroid without a discrete nodule consistent with autoimmune thyroiditis. Thyroid fine needle aspiration (FNA) was non-diagnostic. Thyroid biopsy showed mostly fibrosis with scattered lymphoplasmacytic aggregates, with no evidence of carcinoma, lymphoma, IgG4-related disease, and no Hürthle cell presence. Interestingly, the mesenteric mass biopsy revealed the same pattern. Peripheral flow cytometry and infectious workup were negative. Diagnosis of RT and SM were made. The patient was treated with steroids and improved clinically. The hallmark of RT is the extension of fibrosis beyond the thyroid. This patient exhibited common features of RT such as neck pressure, and pain; female gender, elevated inflammatory markers, nondiagnostic FNA (scant cellularity due to fibrosis), and a positive steroid response. Moreover, intense infiltrative fibrosis mixed with lymphocytes and plasma cells instead of an extensive lymphocytic infiltrate with the germinal center formation on histology supports Riedel’s thyroiditis rather than Hashimoto's. Similarly, SM is a rare, non-neoplastic inflammatory and fibrotic disease that affects the integrity of mesenteric vessels causing common bile duct and ureter obstruction. Negative flow cytometry, the presence of sclerosis, and the absence of bowel/liver lesions involvement make other common causes of a mesenteric mass (lymphoma, desmoid tumor, carcinoid) less likely, supporting the diagnosis of SM. The concurrent timing of her thyroid enlargement and the mesenteric mass as well as the similarity in histology (dense fibrosis with patchy lymphoplasmacytic aggregates) suggests an association between RT and SM. Overall, the case highlights the challenges in diagnosing RT given its extreme rarity and emphasizes the importance of early treatment to prevent systemic involvement.