Hypothyroidism and hyponatremia: data from a series of patients with iatrogenic acute hypothyroidism undergoing radioactive iodine therapy after total thyroidectomy for thyroid cancer.

Abstract

The aim of the present study was to evaluate the role of hypothyroidism as a cause of hyponatremia in a clinical model of iatrogenic acute hypothyroidism due to thyroid hormone withdrawal prior to ablative radioactive iodine (RAI) therapy after total thyroidectomy. The study group consisted of 101 differentiated thyroid cancer (DTC) patients (77 women and 24 men). Plasma concentration of thyroid-stimulating hormone ([TSH]) and sodium ([Na+]) was evaluated before total thyroidectomy (pre[TSH] and pre[Na+]) and on the day of RAI therapy (post[TSH] and post[Na+]). The frequency of hypothyroidism-associated hyponatremia was 4% (4/101). Pre[Na+] was significantly higher than post[Na+] (140.7±1.6 vs 138.7±2.3mEq/L, p=0.012). Moreover, a linear correlation was identified between pre[Na+] and post[Na+]. Iatrogenic acute hypothyroidism-related hyponatremia is uncommon. However, because of the significant reduction of [Na+] in the transition from euthyroidism to iatrogenic hypothyroidism, the value of pre[Na+] should be viewed as a parameter to be considered. Since it acts as an independent risk factor for the development of hyponatremia, patients with a pre[Na+] close to the lower limit of normal range may deserve a closer monitoring of [Na+].