8135 A Rare Case of Late Recurrence of Graves’ Disease Decades After Radioactive Iodine Therapy: Is it Really a Definitive Treatment?

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Abstract Disclosure: K.S. Hill: None. R. Osman: None. Graves’ disease (GD) is the most common cause of hyperthyroidism in the US and worldwide. Radioactive iodine (RAI) therapy has excellent success rates in treatment of GD. Studies have demonstrated that RAI successfully treats GD with a single session in the majority of cases. Recurrence after RAI, if it occurs, is most commonly seen in the first year after RAI. However, this is rare particularly in patients who have developed evidence of successful treatment in the form of post-ablative hypothyroidism. Only a few case reports have demonstrated recurrence of GD more than 10 years after treatment of GD with RAI and development of post-ablative hypothyroidism. We report a case of GD recurrence approximately 30 years after ablation. A 69 y/o woman presented for evaluation of hyperthyroidism and newly discovered thyroid nodule. Her history was significant for GD with orbitopathy diagnosed in the early 1990s and treated with RAI. Following the ablation, she developed hypothyroidism and was managed for over 20 years on levothyroxine therapy. In recent years she began to develop symptoms of palpitations and heat intolerance with biochemical evidence of thyrotoxicosis despite reductions in her levothyroxine dose. She also developed recurrence of her orbitopathy, confirmed by ophthalmology. During this time, a neck CT incidentally described an atrophic thyroid gland with a 9 mm soft tissue nodule in the left thyroid bed. Follow up ultrasound showed a 1.1 cm nodule with increased vascularity in the left thyroid bed with an otherwise atrophic gland and no lymphadenopathy. Her levothyroxine was stopped for one month in preparation for a thyroid uptake scan, during which TSH increased to 15 mcU/mL. Scan showed overall severely decreased radioactive iodine uptake of the gland consistent with prior ablation although there was a faint uptake most focally conspicuous on the left side inferiorly. Thyroid stimulating immunoglobulin (TSI) was elevated at 1.35 IU/L (Ref 0.00-0.55). After discussion with the patient, the decision was made for surgical treatment with thyroidectomy. Pathology was benign. She was continued on her prior dose of levothyroxine 75 mcg daily however now with clinical and biochemical evidence of hypothyroidism requiring continued increase in levothyroxine dose to normalize TSH levels. GD is the most common cause of hyperthyroidism and RAI therapy is the most common definitive treatment for GD in the US. Recurrence of GD after ablative hypothyroidism is rare, particularly in the case of late recurrence decades after ablation. Only a few cases are reported in the literature, ours with the longest interval-to-relapse. Recurrence of orbitopathy may be the first clue. Our case highlights the need to continue to monitor clinically for recurrence of Graves’ disease long after RAI use. Presentation: 6/3/2024