Association between Hypothyroidism and Hyponatremia: An Evidence-Based Literature Review.

Hypothyroidism has traditionally been considered a cause of euvolemic hyponatremia. However, because patients with hypothyroidism often have coexisting conditions that may independently contribute to hyponatremia, it can be difficult to determine whether hypothyroidism is the true underlying cause. This narrative review evaluated 13 retrospective and prospective clinical studies identified through a PubMed search to examine the relationship between hypothyroidism and hyponatremia. Although several pathophysiological mechanisms have been proposed, most studies have failed to demonstrate that hypothyroidism directly causes hyponatremia. Studies reporting an association generally found hyponatremia to occur primarily in patients with severe hypothyroidism, particularly those with myxedema, whereas uncomplicated hypothyroidism was rarely associated with hyponatremia. Similarly, hypothyroidism accounted for only a small proportion of patients presenting with hyponatremia. As most of the available evidence is retrospective, these findings should be interpreted with appropriate caution. Overall, the available clinical evidence does not consistently support a causal relationship between hypothyroidism and hyponatremia in uncomplicated hypothyroidism. When evaluating patients with hyponatremia, hypothyroidism should not be presumed to be the underlying cause, and alternative etiologies should continue to be considered.