Hyponatremia Due to Thyrotropin Deficiency: A Fairy Tale?

Effect of Optimal Thyroid Replacement Therapy on Chronic Hyponatremia with Focused Review of the Evidence, Mechanisms, and Clinical Implications

We present an unusual case of hyponatremia in an ambulatory hypothyroid patient and review related published literature on PubMed including, original articles, reviews and case reports that describe or refute the association and mechanism for the development of hyponatremia in hypothyroidism.

A 50-year-old female presented in ambulatory clinic with complaints of bilateral hand swelling, fatigue, dizziness, and unsteadiness while walking. Laboratory investigations revealed that she had hypothyroidism and hyponatremia. Thyroid hormone replacement therapy resulted in resolution of hypothyroidism symptoms as well as hyponatremia. A comprehensive search of related literature regarding the development of chronic hyponatremia in hypothyroidism revealed two schools of thought, which we have summarized in this report.

Based on our observations, we conclude that due to overlap in symptoms of hyponatremia and neurological manifestations of hypothyroidism, it is imperative to screen hypothyroid patients for underlying hyponatremia and treat accordingly in order to prevent long-term complications of chronic hyponatremia. Hyponatremia secondary to hypothyroidism resolves with appropriate thyroid hormone replacement therapy, which shows convincing evidence of an association between the two entities.

MANAGEMENT OF ENDOCRINE DISEASE: Hypothyroidism-associated hyponatremia: mechanisms, implications and treatment

BACKGROUND

Patients with moderate to severe hypothyroidism and mainly patients with myxedema may exhibit reduced sodium levels (<135 mmol/L).

SUMMARY

The aim of this short review is the presentation of the mechanisms of hyponatremia and of the available data regarding its implications and treatment in patients with hypothyroidism. Hypothyroidism is one of the causes of hyponatremia, thus thyroid-stimulating hormone determination is mandatory during the evaluation of patients with reduced serum sodium levels. The main mechanism for the development of hyponatremia in patients with chronic hypothyroidism is the decreased capacity of free water excretion due to elevated antidiuretic hormone levels, which are mainly attributed to the hypothyroidism-induced decrease in cardiac output. However, recent data suggest that the hypothyroidism-induced hyponatremia is rather rare and probably occurs only in severe hypothyroidism and myxedema. Other possible causes and superimposed factors of hyponatremia (e.g. drugs, infections, adrenal insufficiency) should be considered in patients with mild/moderate hypothyroidism. Treatment of hypothyroidism and fluid restriction are usually adequate for the management of mild hyponatremia in patients with hypothyroidism. Patients with possible hyponatremic encephalopathy should be urgently treated according to current guidelines.

CONCLUSIONS

Severe hypothyroidism may be the cause of hyponatremia. All hypothyroid patients with low serum sodium levels should be evaluated for other causes and superimposed factors of hyponatremia and treated accordingly.

SIAD: practical recommendations for diagnosis and management

Hyponatremia is the commonest electrolyte disturbance encountered in hospitalized patients, and the syndrome of inappropriate antidiuresis (SIAD) is the most frequent underlying disorder. There is a well-recognized relationship between hyponatremia and increased morbidity and mortality. Therefore, to provide appropriate treatment is critical to improve the clinical outcome related to SIAD-hyponatremia. There have been important advances in the treatment of SIAD over the last decade, leading to the publication of several clinical guidelines. In particular, the introduction of the vasopressin-2 receptor antagonists provides a potent pharmacological tool to target the underlying pathophysiology of SIAD. The evidence base recommendations of the available therapies for SIAD are discussed in this study. Fluid restriction is considered the first-line therapy by the recent published guidelines, but it is certainly ineffective or unfeasible in many patients with SIAD. We discuss a number of relevant points to the use of fluid restriction in this study, including the lack of good evidence-based recommendations to support its use. Conversely, the clinical efficacy of oral tolvaptan in SIAD supported by good quality randomized, placebo controlled, clinical trials. However, the cost of the therapy and the need for long-term safety data may limit its widespread use. Finally, new recommendations for the management of acute hyponatremia with a focus on the use of bolus therapy with 3 % hypertonic sodium chloride are described in this study.