MON-877 - Post-Roux-En-Y Gastric Bypass Autoimmune Thyroid Transition: Hashimoto'S to Graves Disease in A Postmenopausal Female

Background: Bariatric surgery, particularly Roux-en-Y gastric bypass (RYGB), alters metabolic, nutritional and immune regulation. While transition of thyrotoxicosis to euthyroidism or hypothyroidism is well documented, rare autoimmune shifts from Hashimoto's disease (HD) associated hypothyroidism to Graves disease (GD) associated hyperthyroidism are uncommon. The occurrence of this shift with RYGB as the sentinel trigger event is rare and clinically challenging, highlighting the complex interplay between weight loss, immune modulation, and thyroid autoantibody balance. Our clinical case highlights this.

Case Presentation: We report a 51-year-old postmenopausal woman with HD associated hypothyroidism diagnosed at age 27 who had been on long term thyroid hormone repletion therapy. She underwent RYGB in 2017 and discontinued levothyroxine after developing postoperative euthyroidism. The surgery was associated with ~ 116lb maximum weight loss with no significant interval weight regain. Her nadir weight post RYGB was under 100lbs with a current weight of 119lbs and BMI of 22.5kg/m2. In 2024, routine labs revealed declining TSH with rising anti-TPO, anti-thyroglobulin, and Thyroid stimulating immunoglobulin (TSI) antibodies. By late 2024, she developed hyperthyroidism (suppressed TSH, elevated free T4, TSI up to 150%) Thyroid ultrasound showed diffuse hypoechogenicity and hypervascularity with no noteable thyroid nodular disease, confirming GD on a background of chronic autoimmune thyroiditis. Methimazole initially controlled hyperthyroidism but caused treatment-induced hypothyroidism (TSH 0.088 µIU/mL, free T4 0.7 ng/dL), prompting transition to “block-and-replace therapy” with concomitant low-dose methimazole; 5mg QOD and low dose levothyroxine 37.5mcg QD, stabilizing her thyroid functional and clinical status. Nutritional studies excluded micronutrient deficiency including normal serum iodine and selenium levels. She is also being managed for dumping syndrome, reactive hypoglycemia and osteopenia.

Discussion: This case illustrates immune-mediated autoantibody switch with transition from HD associated hypothyroidism to GD associated hyperthyroidism. While the exact etiopathogenetic mechanism underlying this is unclear, the role of RYGB as the sentinel inciting event in our patient is strongly suggested by the temporal clinical course of the patient. Studies suggesting a “thyroid-gut” axis and the impact of marked weight loss such as following RYGB on modulating gut microbiota and altering immune balance may have a role in this observed clinical phenomenon.

Conclusion: Post-bariatric patients may develop rare autoimmune thyroid transitions years after surgery. Long-term monitoring of thyroid functional status are essential to maintain euthyroidism in post bariatric surgery patients with known autoimmune thyroid disease.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*