What is the relationship between hyperthyroidism and hyponatremia (low sodium levels)?

From the Guidelines

Hyperthyroid patients with hyponatremia should be treated with anti-thyroid medications and managed with fluid restriction and monitoring, as correcting the underlying thyroid dysfunction is key to normalizing sodium levels. The treatment of hyperthyroidism-induced hyponatremia involves addressing the underlying cause of the condition, which is the excessive production of thyroid hormones [ 1 ].

Mechanisms and Treatment

Hyperthyroidism can cause hyponatremia through several mechanisms, including increased renal blood flow leading to decreased sodium reabsorption, increased antidiuretic hormone (ADH) release, and altered thirst regulation [ 1 ]. The hypermetabolic state associated with hyperthyroidism also increases sweating and fluid losses, potentially worsening electrolyte imbalances. Treatment should focus on controlling the hyperthyroid state with medications such as methimazole (10-30 mg daily) or propylthiouracil (100-300 mg daily), and managing symptoms with beta-blockers like propranolol (20-40 mg every 6-8 hours) [ 1 ].

Management of Hyponatremia

For patients with euvolemic hyponatremia, fluid restriction to 800-1000 mL/day is recommended [ 1 ]. In cases of severe symptomatic hyponatremia (sodium <120 mEq/L with neurological symptoms), hypertonic saline (3%) at 0.5-2 mL/kg/hour may be necessary, with careful monitoring to avoid rapid correction [ 1 ]. It's essential to regularly monitor both thyroid function tests and serum sodium levels, as sodium levels typically normalize once the hyperthyroid state is controlled [ 1 ].

Considerations

While vasopressin antagonists may be considered in certain cases of hyponatremia, such as in patients with heart failure [ 1 ], their use in hyperthyroid-induced hyponatremia is not well-established, and treatment should prioritize correcting the underlying thyroid dysfunction. Regular monitoring and adjustment of treatment as necessary are crucial to managing hyperthyroidism and associated hyponatremia effectively [ 1 ].

From the Research

Hyperthyroidism and Hyponatremia

• Hyperthyroidism is characterized by an excessive concentration of thyroid hormones in tissues, which can be caused by increased synthesis of thyroid hormones, excessive release of preformed thyroid hormones, or an endogenous or exogenous extrathyroidal source 2.
• The most common causes of hyperthyroidism are Graves' disease, toxic multinodular goiter, and toxic adenoma 2.
• Hyponatremia, on the other hand, is often associated with hypothyroidism, particularly in patients with severe hypothyroidism and myxedema 3, 4.
• The mechanism of hyponatremia in hypothyroidism is thought to be due to impaired free water excretion and changes in sodium handling in the kidney 3, 4.
• However, there is limited evidence to suggest a direct link between hyperthyroidism and hyponatremia, and other potential etiologies should be considered in patients with severe hyponatremia 4.
• Treatment of hyperthyroidism typically involves antithyroid medications, radioactive iodine ablation, or surgical thyroidectomy, while treatment of hyponatremia in patients with hypothyroidism usually involves treatment of the underlying hypothyroidism and fluid restriction 3, 2.

Treatment Options

• Antithyroid medications, such as methimazole and propylthiouracil, are commonly used to treat hyperthyroidism 2, 5.
• Radioactive iodine ablation is also a widely used treatment for hyperthyroidism, particularly in the United States 2.
• Treatment of hyponatremia in patients with hypothyroidism typically involves treatment of the underlying hypothyroidism and fluid restriction, although other potential etiologies should be considered in patients with severe hyponatremia 3, 4.

Clinical Implications

• Hyperthyroidism can have significant clinical implications, including cardiac arrhythmias, heart failure, osteoporosis, and adverse pregnancy outcomes 6.
• Hyponatremia can also have significant clinical implications, particularly in patients with severe hyponatremia, and requires prompt treatment to prevent complications such as hyponatremic encephalopathy 3, 4.