Iatrogenic Hyperthyroidism With Recurrent Functioning Thyroid Tissue 40 Years After Thyroidectomy for Graves’ Disease

Background: Graves’ disease is an immune-mediated cause of thyrotoxicosis treated with anti-thyroid drugs (ADTs), radioactive iodine (RAI) or thyroidectomy. Thyroidectomy has been documented to have the lowest rate of recurrence amongst treatment options(1). Data regarding long-term recurrence rates is limited beyond 54 months. Clinical Case: An asymptomatic 59 year old female was found to have recurrent thyrotoxicosis on routine laboratory testing. The patient underwent thyroidectomy at age 19 years for Graves’ disease. Prior records unavailable to clarify initial surgical intervention. The patient had post-surgical hypothyroidism which was managed with levothyroxine 100mcg once daily for over 20 years. A biochemically euthyroid state was clearly documented on prior laboratory testing. Initial laboratory testing with TSH <0.01mIU/L (0.45-4.50), FT3 2.8ng/dL (0.8-1.7). Levothyroxine was discontinued with persistent thyrotoxicosis after 8 weeks: TSH <0.01, FT3 5.7, FT4 1.74. Radioactive Iodine Uptake and scan was obtained after administration of 6uCi of iodine-131 which demonstrated 50.8% uptake of radioactive iodine at 24 hours (Normal 10-30%). The left thyroid gland was noted to be in normal position and enlarged with diffuse increase intensity of radiotracer uptake. The right thyroid gland was surgically absent. The patient subsequently underwent completion thyroidectomy with endocrine surgery with resolution of hyperthyroid state. Surgical pathology was benign and consistent with Graves’ disease and multinodular goiter. The patient did become hypothyroid post-operatively and required levothyroxine replacement. She is clinically and biochemically euthyroid on levothyroxine 100mcg once daily 14 months post-operatively. Conclusion: This is a case of recurrent hyperthyroidism approximately 40 years after definitive treatment with thyroidectomy. Although it is unclear whether patient underwent total thyroidectomy or subtotal thyroidectomy for initial intervention, the recurrence of thyrotoxicosis after such a long period of time has not previously been reported in the literature to the knowledge of this writer. This has important implications regarding the underlying pathophysiology of Graves’ disease and the ability of remnant thyroid tissue to regenerate over time. This also has important implications for long-term monitoring in patients with history of thyroidectomy for Graves’ disease. Reference: 1. Sundaresh, V., Brito, J. P., Wang, Z., Prokop, L. J., Stan, M. N., Murad, M. H., & Bahn, R. S. (2013). Comparative effectiveness of therapies for Graves’ hyperthyroidism: a systematic review and network meta-analysis. The Journal of clinical endocrinology and metabolism, 98(9), 3671–3677.