What is Euthyroid Sick Syndrome : Causes, Symptoms, Treatment, Prognosis, Pathphysiology, Complications, Epidemiology

The thyroid gland is a ductless butterfly shaped endocrine gland found at the base of the neck below the laryngeal prominence or the Adam’s apple. The thyroid gland releases hormones that help in regulating the vital functions of the human body. It controls metabolism, and basic growth and development of the body. Thyroid gland helps in regulation of respiration, heart rate, nervous system, muscle strength, body weight, cholesterol levels, body temperature, menstrual cycle etc.

The two main hormones released by the thyroid glands, known as T3 and T4, regulate the functioning in the body. Any increase or decrease in the levels of T3 and T4 leads to hyperthyroidism or hypothyroidism, both of which have adverse effects on the body. In most of the cases, abnormal level of T3 or T4 hormone in the body is caused due to abnormal functioning of the thyroid gland. However, in certain cases, it has been noticed that there is an abnormal finding in the thyroid function test without actual dysfunction of the thyroid glands. This condition is known as euthyroid sick syndrome.

Euthyroid is a medical term used to define a state where the thyroid glands functions within normal limits. Euthyroid sick syndrome is a condition characterised by abnormal findings on thyroid function tests in the absence of hypothalamic-pituitary and thyroid gland dysfunction. These abnormal findings in thyroid function test are commonly associated with conditions such as:

• Underlying systemic diseases such as renal diseases, cardiovascular diseases, pulmonary diseases, gastrointestinal diseases etc.
• Metabolic disorders
• Chronic illness such a diabetes
• Inflammatory conditions
• Fasting and starvation
• Trauma
• Burns and sepsis
• Myocardial infarction
• Stress
• Malignancies
• Surgeries such as bone marrow transplantation.

Euthyroid sick syndrome very often mimics hypothyroidism. It is a condition in which the patient generally exhibits signs and symptoms of hypothyroidism such as:

• Excessive tiredness or fatigue
• Weight gain
• Disturbed sleep or insomnia
• Dryness in skin
• Depression and mood changes
• Increased anxiety level
• Adrenal fatigue.

As mentioned earlier, euthyroid sick syndrome affects people with acute and chronic conditions. It is common among patients with critical illness. It affects up to 70% of hospitalized patients with above mentioned conditions, especially in the ICUs.

The prognosis of euthyroid sick syndrome is good. The condition is generally reversible and treatable. The abnormalities normalize once the underlying condition is treated.

Euthyroid sick syndrome is generally associated with underlying medical conditions, which may be acute or chronic in nature. It is commonly seen in association with fasting, starvation, anorexia, pneumonia, trauma, critical cases in ICU, stress, post cardiopulmonary bypass, renal failure, diabetic ketoacidosis, liver cirrhosis, sepsis etc.

The actual pathogenesis of euthyroid sick syndrome is still unknown and a lot of research is going on. The most accepted theory claims that euthyroid sick syndrome is caused by decreased peripheral conversion of T4 to T3. There is decreased clearance of reverse T3 that has been generated by T4 and also decreased binding of thyroid hormones to TBG (thyroxine-binding globulin). Studies have proven that cytokines such as tumour necrosis factor –alpha, IL-1 play a vital role in development of euthyroid sick syndrome.

Euthyroid sick syndrome may often get misdiagnosed by hypothyroidism. As such this condition does not have any specific complications. However, there may be complications based on the severity of the underlying condition. If the causative factor is not rightfully diagnosed and treated, there may be secondary complications associated with it.

Diagnosis of euthyroid sickness syndrome includes extensive lab work for determining the serum thyroid hormone levels. The affected individual may have slightly elevated, low or normal TSH level based on intensity of the condition. Total T3 and T4 levels are generally altered with reverse T3 above normal limits. Free T3 is below normal limits and in extreme cases, free T4 is also below normal limits. Euthyroid sick syndrome is commonly seen in association with TACITUS syndrome, and thus, these patients may also have hyperprolactinemia and increased levels of cortisol and growth hormones.

Treatment planning for euthyroid sick syndrome is done by an experienced physician or an endocrinologist. The treatment planning involves identification of underlying systemic disorder causing euthyroid sick syndrome and treating the same. Thyroid hormone replacement is not always indicated; however, based on the lab findings, a short term course of certain thyroid specific medication may help in management of the condition and reversing the condition. Specific supplements may be given for management of adrenal function, stress and other symptomatic conditions. In some cases, administration of intravenous vitamins is recommended. One can also consider lifestyle modification and treatment with alternative medications, acupuncture and even massage therapy for euthyroid sick syndrome.

Euthyroid sick syndrome is a condition that generally affects individuals with other acute and chronic conditions. It is more common among patients admitted in critical care unit. Euthyroid sick syndrome is characterized by abnormal thyroid blood test but with normal functioning of the thyroid glands. It is a reversible condition and treatment involves treatment of the underlying condition. Specific thyroid medications may be given based on the severity of the condition, but in most of the condition it has been seen that it normalizes by itself without definitive treatment.

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