Subclinical hyperthyroidism means that a person has low or undetectable levels of thyroid-stimulating hormone (TSH) with normal levels of free thyroid hormones. It usually does not cause symptoms.

The pituitary gland in the brain produces TSH to regulate the production and release of thyroid hormones by the thyroid gland. These hormones play a crucial role in regulating metabolism and bodily functions.

If a person has low thyroid hormone levels, the pituitary gland produces more TSH to tell the thyroid gland to produce more hormones. Conversely, the pituitary gland produces less TSH if thyroid hormone levels are high.

Around 1–2 people in 100 have subclinical hyperthyroidism.

These individuals may not experience any symptoms or require treatment. However, this depends on the person’s age and general health.

Read on to learn about subclinical hyperthyroidism, its symptoms, causes, diagnosis, treatment, and more.

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Subclinical hyperthyroidism is a condition that often goes unnoticed.

In typical hyperthyroidism, the thyroid gland is overactive, and people experience symptoms such as:

A person with subclinical hypothyroidism may experience similar symptoms but typically less severe. They also may have no symptoms at all.

Read more about subclinical hypothyroidism.

Subclinical hyperthyroidism has various causes. These include both exogenous (internal) and endogenous (external) factors.

Exogenous causes are more common. For example, a person with an underactive thyroid gland may take medications to replace thyroid hormones. If they take too much, they may develop subclinical hyperthyroidism.

Endogenous causes of subclinical hyperthyroidism include:

  • Graves’ disease: This autoimmune disorder causes the thyroid to overproduce thyroid hormones.
  • Multinodular goiter: This is an enlarged thyroid gland with multiple nodules. Sometimes, there may only be one thyroid nodule, known as a thyroid adenoma.
  • Thyroiditis: This is a condition where the thyroid gland is inflamed.

Diagnosing subclinical hyperthyroidism usually involves a series of blood tests to measure levels of TSH.

Healthcare professionals typically split subclinical hyperthyroidism into two categories:

  • Grade I: TSH levels are between 0.1 and 0.39 milli-international units per liter (mIU/L).
  • Grade II: TSH levels are less than 0.1 mlU/L.

In addition to blood tests, a doctor will perform a physical examination to check for any signs of thyroid dysfunction, such as an enlarged thyroid gland or hand tremors. They may also order imaging tests, such as a thyroid ultrasound, to evaluate the structure of the thyroid gland.

Doctors treat subclinical hyperthyroidism on a case-by-case basis. They will consider the individual’s overall health and the treatment’s potential risks and benefits.

Their recommended treatment plan may depend on several factors, including:

  • the underlying cause of subclinical hyperthyroidism
  • the individual’s age
  • the individual’s overall health and any other medical conditions
  • complications

Sometimes, subclinical hyperthyroidism may not require treatment and will resolve on its own.

If the individual does not have noticeable symptoms or an increased risk of developing other health problems, they may undergo regular monitoring instead. However, if a person has an underlying condition causing subclinical hyperthyroidism, treatment aims to address these issues — for example, surgery to remove the thyroid gland.

In some cases, doctors prescribe medications. These may include beta-blockers or antithyroid drugs to reduce the production of thyroid hormones and alleviate symptoms.

Healthy levels of thyroid hormones are important for overall health, and untreated subclinical hyperthyroidism may cause complications. These may include:

  • increased risk of hyperthyroidism
  • adverse heart health effects
  • decreased bone density in postmenopausal people

A person’s outlook depends on the underlying cause of subclinical hypothyroidism.

When the cause is Graves’ disease or toxic multinodular goiter, the treatment has a high success rate, and the outcomes are good. However, as with any disease, the outlook depends on the individual and how they respond to treatment.

Anyone experiencing the symptoms of hyperthyroidism should contact their doctor for an assessment. Early diagnosis and treatment can help avoid complications.

Furthermore, anyone with diagnosed subclinical hyperthyroidism should see their doctor if they experience significant changes to their symptoms or overall health. They should also attend regular monitoring appointments to ensure that their treatment is effective and they are not experiencing any adverse effects or disease progression.

Subclinical hyperthyroidism is a condition characterized by low or undetectable levels of TSH with normal levels of free thyroid hormones. It can be due to underlying health conditions or excessive thyroid hormone replacement therapy.

Diagnosis typically involves blood tests to measure TSH and free thyroid hormone levels and a physical examination.

Treatment options depend on the condition’s underlying cause and may include medications, surgery, or regular monitoring. In some cases, a person may not need treatment.