Do Patients with Differentiated Thyroid Cancer Face the Risk of Hyponatremia at the Expense of Preparation for Radioactive Iodine Treatment?

Objective: Differentiated thyroid cancer (DTC) is the most common endocrine cancer. The main therapeutic strategies are surgery and radioactive iodine (RAI) treatment in selected intermediate- and high-risk patients. Hyponatremia is the most frequent form of electrolyte imbalance and few studies have assessed the frequency and clinical impact of hyponatremia in patients with thyroid cancer. In this study, we aimed to determine the prevalence and severity of hyponotsignnatremia among hypothyroid patients in the peri-ablation period. The secondary objective was to assess the correlation between Sodium (Na) level and hypothyroidism severity, age, and RAI dosage. Methods: A total of 51 patients with DTC who were referred to our Nuclear Medicine Department for RAI ablation/treatment were enrolled. Serum Na, thyroid-stimulating hormone ( TSH), and free triiodothyronine and thyroxine levels were measured three times during the study (under LT4 suppression, when the patient was hypothyroid before and after receiving RAI). Baseline, pre-, and post-RAI mean serum Na and other hormonal parameters were compared. The number of patients with hyponatremia and possible related symptoms were noted. Correlation of serum Na levels with age, RAI dosage, and hypothyroidism severity was determined. Results: The number of patients with hyponatremia did not differ significantly in the baseline, pre-, and post-RAI periods. None of the patients experienced moderate-to-severe hyponatremia. There was no significant correlation between serum Na levels and age, serum TSH, or the hormone levels. Conclusion: In conclusion, preparation for RAI treatment with LT4 withdrawal and or a low-iodine diet is not a common etiological factor for the development of hyponatremia in patients with DTC.