Sick euthyroid syndrome

Sick euthyroid syndrome (SES), also known as nonthyroidal illness syndrome (NTIS), is a condition characterized by abnormal thyroid function tests encountered in patients with acute or chronic systemic illnesses. The laboratory findings are similar to those seen in subclinical hypothyroidism, but the clinical picture is often complicated by the underlying illness.

Etiology

The exact cause of sick euthyroid syndrome is not known. It is believed to be a result of the body's response to severe illness, such as sepsis, surgery, or trauma. The body may reduce the levels of thyroid hormones in the blood in an attempt to conserve energy and resources for healing.

Pathophysiology

In sick euthyroid syndrome, the levels of thyroid-stimulating hormone (TSH) are usually normal or slightly decreased, despite low levels of circulating thyroid hormones (triiodothyronine (T3) and thyroxine (T4)). This is in contrast to primary hypothyroidism, where TSH levels are elevated in response to low thyroid hormone levels. The reduction in T3 and T4 levels is thought to be due to alterations in the peripheral conversion of T4 to T3, decreased thyroid hormone secretion, and changes in thyroid hormone binding.

Clinical Features

Patients with sick euthyroid syndrome are typically critically ill and may present with a wide range of symptoms depending on the underlying illness. The thyroid dysfunction is usually asymptomatic and is often discovered incidentally on routine blood tests.

Diagnosis

Diagnosis of sick euthyroid syndrome is primarily based on laboratory findings of low T3 and T4 levels with normal or slightly decreased TSH levels in the setting of non-thyroidal illness. Other causes of thyroid dysfunction, such as primary hypothyroidism or hyperthyroidism, should be ruled out.

Treatment

Treatment of sick euthyroid syndrome primarily involves managing the underlying illness. Thyroid hormone replacement therapy is generally not recommended, as it has not been shown to improve outcomes and may potentially cause harm.

Prognosis

The prognosis of sick euthyroid syndrome is largely dependent on the severity and course of the underlying illness. The thyroid dysfunction usually resolves once the acute illness is treated.

Sick euthyroid syndrome Resources
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