Relative Adrenocortical Insufficiency Following Radioactive Iodine Therapy for Graves’ Disease: A Report of Two Cases

INTRODUCTION: In recent years, radioactive iodine (RAI) therapy has become a main choice for Graves’ disease. The rapid release of thyroid hormones following RAI may on occasion trigger severe events, such as thyroid storm or heart block. This study presents two cases of possible acute adrenocortical insufficiency precipitated by radioiodine therapy. CASE PRESENTATION: Two females aged 65 and 19 years with long-standing Graves’ disease underwent radioiodine treatment at our clinical center. Both patients suffered nausea, fatigue, aggravated palpitation, and relative hypotension thereafter. Laboratory data showed severe thyrotoxicosis with free thyroxine higher than three times the upper limit, while basal serum cortisol (8 AM) was below the lower limit (5.08 μg/dL and 2.08 μg/dL respectively) under stress, indicating a potential relative adrenocortical insufficiency. There was then full recovery after adequate hydrocortisone therapy. As thyrotoxicosis resolved, the levels of basal cortisol were subsequently raised to normal. CONCLUSION: Post-RAI adrenocortical insufficiency might occur in patients with severe Graves’ disease. Basal serum cortisol might be a cost-effective parameter for the identification of potential patients.