The thyroid is a small, butterfly-shaped gland located at the base of your neck. It plays an important role in the body’s metabolism by producing and releasing hormones, mainly thyroxine (T4) and triiodothyronine (T3). These hormones influence how quickly your body uses and stores energy. They also impact various bodily functions including heart rate, body weight, energy levels, and skin health. The production and release of T4 and T3 are regulated by thyroid-stimulating hormone (TSH), which is secreted by the pituitary gland. This regulatory process is part of the hypothalamic-pituitary-thyroid (HPT) axis, ensuring that thyroid hormone levels remain within a normal range.
Now, imagine getting a blood test result showing low thyroid hormone levels. Normally, this might point to hypothyroidism, a condition where the thyroid gland isn’t producing enough thyroid hormones. But, it could be something else. Sometimes, these low levels can happen due to a different reason entirely, and you might not actually have a thyroid problem. This is called euthyroid sick syndrome (ESS).
Euthyroid Sick Syndrome (ESS), also known as non-thyroidal illness syndrome (NTIS), is a state where your body’s response to illness throws your thyroid hormone levels off balance. Even though the test results show low levels, your thyroid gland itself is working normally. This syndrome is commonly seen in hospitalized patients, especially those with severe illnesses or conditions that aren’t thyroid-related, such as pneumonia, sepsis, malnutrition (due to starvation or eating disorders), heart failure, kidney disease, liver disease, and HIV.
This article answers some questions regarding the causes, symptoms, diagnosis, and treatment of euthyroid sick syndrome.
Why do thyroid hormone levels drop in euthyroid sick syndrome?
The exact reasons are still being explored, but it likely involves a complex interplay between inflammation and how the body uses thyroid hormones.
Normally, the hypothalamus, pituitary gland, and the thyroid gland work together to regulate thyroid hormone production. However, in response to starvation or severe illness, the body undergoes several changes to conserve energy for recovery, which affects various hormonal systems including the hypothalamic-pituitary-thyroid axis. Here’s how the process typically unfolds:
- Inflammation and the production of cytokines: Inflammation (the body’s response to illness or injury) and the release of cytokines can lead to an altered metabolism of thyroid hormones, specifically a reduction in the conversion of inactive T4 to the active hormone T3. These changes, however, occur because they help conserve energy during illness.
- Increase in rT3 Levels: As a result of the decreased conversion to T3, there’s an increase in the reverse T3 (rT3) levels.
What are the symptoms of euthyroid sick syndrome?
The tricky thing about ESS is that it often doesn’t cause any specific symptoms itself. This is because the symptoms you might experience are more likely due to the underlying condition that triggers the ESS. For example, if you have ESS due to pneumonia, you’ll likely feel fatigued and short of breath because of the pneumonia, not the ESS.
How is euthyroid sick syndrome diagnosed?
The key to diagnosing ESS, and essentially differentiating it from an actual thyroid gland disorder, lies in understanding the bigger picture. However, drawing this distinction can be challenging, especially in patients with a critical or chronic illness. This is because the effects of various medications and treatments in hospital settings can complicate the interpretation of thyroid function tests.
In order to accurately diagnose ESS, your doctor will consider your medical history, symptoms (in relation to any underlying illnesses you might have), and your thyroid function test results. Say your rT3 levels are high and thyroid hormone levels are low (especially T3), but your TSH (thyroid-stimulating hormone) levels are normal or only slightly elevated. Then it’s likely that you have ESS.
Sometimes, though, a thyroid ultrasound may be needed to distinguish between ESS and hyperthyroidism. Hyperthyroidism is characterized by decreased levels of TSH and increased levels of FT4, and this hormonal pattern can sometimes be observed in ESS. In this case, a thyroid ultrasound helps by showing changes in the thyroid gland itself that are characteristic of hyperthyroidism, such as increased blood flow or nodules, which would not typically be present in ESS.
How is euthyroid sick syndrome treated?
The good news is that ESS itself doesn’t require specific treatment. The focus is on treating the underlying illness that caused it. As you recover from that illness, your thyroid hormone levels should naturally return to normal.
Key takeaways
- Euthyroid sick syndrome is a condition where low thyroid hormone levels are caused by an underlying illness, not a problem with the thyroid gland itself.
- It often doesn’t cause its own symptoms, and the symptoms you experience are more likely due to the underlying illness.
- There’s no specific treatment for euthyroid sick syndrome, but addressing the underlying illness should resolve the thyroid hormone imbalance.
- The understanding of euthyroid sick syndrome helps healthcare providers to avoid unnecessary interventions in an attempt to re-normalize thyroid hormone levels.
