SUN-LB84 Riedel’s Thyroiditis: A Diagnostic and Therapeutic Challenge

Background: Riedel’s thyroiditis is a rare thyroid pathology which presents a challenge for clinicians to diagnose and treat. Etiology remains largely unknown, although data suggests an association with Hashimoto thyroiditis, systemic fibrosis, and IgG-4 related systemic disease. Presentation of Riedel’s thyroiditis can mimic malignant thyroid neoplasm, lymphoma, or a fibrous variant of Hashimoto thyroiditis. Due to its rarity, there is no consensus on the treatment. Clinical case: A 36-year old woman presented with a two-month history of gradually progressing neck swelling. She developed associated neck pain, decreased range of motion, hoarseness, and dysphagia, without difficulty breathing. One year prior to presentation, she had been diagnosed with hypothyroidism. She did not have a family or personal history of thyroid malignancy, however, she lived near Chernobyl during her childhood. On exam, the anterior and lateral neck was hard and enlarged, but nontender. The neck range of motion was diminished. The initial ultrasound of the thyroid demonstrated asymmetrically enlarged heterogenous diffusely nodular right thyroid and isthmus measuring 1.9cm. A CT of the chest with contrast showed diffusely enlarged thyroid extending superiorly beyond the image with mild tracheal displacement. Initial laboratory results included TSH of 17.40 uU/ml (ref: 0.35-4.94 uU/ml), free T4 of 1.06 ng/dl (ref: 0.61-1.82 ng/dl). She had a significantly increased thyroid autoantibodies (Anti-TPO >700 IU/ml with ref: 0.0-9.0 IU/ml, Anti-TG >2000 IU/ml with ref: 0.0-4.0 IU/ml). PTH and calcium were normal, and calcitonin was low. In the interim, the patient was evaluated by ENT without evidence of airway compromise. She underwent a core biopsy of the right thyroid lobe which demonstrated dense fibrous connective tissue mixed with mature lymphocytes. Pathology and immunostaining results were suggestive of Riedel’s thyroiditis. The patient was started on prednisone 60mg daily, which she tolerated for 6 weeks. Due to side effects, prednisone dose was titrated down and tamoxifen was added. Over the following 6 months, compressive symptoms resolved, and the ultrasound showed a significant decrease in the thyroid size. TSH normalized with thyroid hormone replacement. To date, she is asymptomatic and continues on tamoxifen and low dose prednisone without evidence of progression. Conclusion: Riedel’s thyroiditis is a rare condition that can progress into a medical emergency and should be suspected in patients presenting with a thyroid mass. Clinical awareness of Riedel’s symptomatology and laboratory findings should enhance our ability to distinguish and make the diagnosis. Instituting effective treatment that results in the improvement of symptoms and reduction in thyroid size can be challenging due to possible poor response or development of side effects.