Counting Chickens Before They Hatch – Transient Hypothyroidism after Radioiodine Therapy in Graves’ Disease

Background Graves' disease (GD) is the most common cause of hyperthyroidism and presents with systemic and ophthalmic features. Radioiodine therapy (RIT) and surgery are considered definitive therapies because they result in hypothyroidism and require lifelong levothyroxine (LT4) replacement. Hypothyroidism typically occurs within 3 to 6 months after RIT, and patients are usually started on a full dose of LT4 to treat hypothyroidism. RIT failure is reported in about 20% of patients with persisting thyrotoxicosis, necessitating a repeat dose of RIT after 6 months. However, recurrence of GD after RIT-induced hypothyroidism is rarely observed. Case report We report a young woman with long-standing GD that was not controlled with antithyroid drugs (ATD) and who received RIT. She developed hypothyroidism 3 months after RIT, which gave us a sense of assurance of a complete cure. However, she developed recurrent thyrotoxic features within 4 months, prompting us to withdraw LT4 therapy. Re-evaluation revealed a recurrence of GD. Discussion GD is managed with antithyroid drugs (ATD), radioiodine therapy (RIT), and thyroidectomy in certain situations. Hypothyroidism after RIT is considered permanent, with lifelong LT4 replacement. Recurrence of GD in post-RIT hypothyroidism has been described, with reactivation of stimulating antibodies, thyroid stunning, and development of thyroid malignancy. Conclusion Our case highlights the occurrence of transient hypothyroidism after RIT and characterizes its profile.