Thyroid Autonomy and Disseminated Thyroid Autonomy in Hyperthyroidism Caused by an Autonomous Adenoma

Brain regions such as the hypothalamus and the pituitary gland control thyroid hormone production. Neurotransmitters from the hypothalamus and pituitary gland stimulate thyroid cells to release thyroid hormones or to reduce hormone production.

Thyroid hormones regulate important metabolic processes in the body. Even in healthy individuals, isolated cells in the thyroid tissue exist that are not subject to the overarching control of the hypothalamus and pituitary gland.

However, their activity has little effect on metabolism. The situation is different when entire sections of the thyroid gland act autonomously and produce hormones on their own.

The thyroid is a hormone-producing gland located in the neck below the larynx and in front of the trachea @ Rasi /AdobeStock

The following forms are possible:

• Thyroid autonomy can be unifocal, meaning it occurs in a specific area of the thyroid gland. This form of thyroid autonomy is often accompanied by tissue overgrowth (adenoma).
• Doctors refer to thyroid autonomy as multifocal when the autonomous cells occur in multiple locations within the thyroid gland.
• In rare cases, autonomous cells can also develop completely freely within the thyroid tissue. Experts refer to this as disseminated thyroid autonomy.

Thyroid autonomy often leads to an overactive thyroid (hyperthyroidism). Another common cause of hyperthyroidism is Graves’ disease, in which the body mistakenly produces antibodies against the TSH receptor in the thyroid gland (autoimmune thyroiditis).

The most important cause of thyroid autonomy is iodine deficiency. This leads to an iodine-deficient goiter (“goiter”).

The iodine deficiency causes uncontrolled growth of cells within the thyroid gland. The body therefore attempts to absorb more iodine by producing more cells. Eventually, cells become decoupled from the regulatory loop (autonomous) and, when iodine is supplied, begin uncontrolled hormone production.

Another cause of unifocal thyroid autonomy is genetic mutations that make it difficult for the cells to respond to neurotransmitters in the brain. This loss of control also leads to increased cell growth and autonomous hormone production.

Symptoms often do not appear until later in life, as thyroid autonomy develops quite slowly. Typically, nodular growths develop in the thyroid tissue, causing difficulty swallowing or breathing problems. At this point, those affected usually seek medical attention.

In addition, unchecked hormone production in thyroid autonomy leads to noticeable changes in the body’s metabolism.

Those affected may experience symptoms such as:

• Rapid heartbeat (tachycardia)
• Weight loss
• Feeling of heat
• Psychomotor agitation
• Sleep disturbances
• Hair loss
• Diarrhea and digestive problems
• Menstrual cycle problems in women
• Diagnosis of thyroid autonomy

Radiology is responsible for visualizing autonomously active areas within the thyroid gland. There, doctors can use radioactively labeled iodine (scintigraphy) to make the active cells visible.

Areas within the thyroid gland that exhibit a high degree of autonomy are visualized as “hot nodules” via scintigraphy. In addition, it is possible to diagnose thyroid autonomy using certain blood tests.

Here, the levels of thyroid hormone and thyroid-stimulating hormone (TSH) play a central role. In suspected cases, autoantibodies that can lead to inflammation of the thyroid gland—such as in Graves’ disease—are also examined.

Scintigraphy is a functional imaging test for the thyroid gland using a gamma camera @ Werner /AdobeStock

Drug therapies (e.g., thyrostatic agents) cannot cure the underlying cause of thyroid autonomy. Therefore, they are often used only for a limited time, for example, to prepare the patient for surgery.

The number of autonomous cells in the thyroid gland can be reduced either chemically or surgically.

Chemical methods include radioiodine therapy and sclerotherapy using alcohol.

• In radioiodine therapy, targeted treatment with radioactively labeled iodine leads to cell death in the autonomously active cells.
• In sclerotherapy, doctors inject alcohol into the affected areas, which also results in cell death. The body then replaces the dead cells with connective tissue (sclerosis).

If curative treatment is not possible, thyroidectomy may be an option. In this procedure, doctors surgically remove the thyroid gland, which ultimately requires lifelong thyroid hormone replacement therapy.

In rare cases, a thyrotoxic crisis may occur. This is a life-threatening emergency characterized by rapid heartbeat, arrhythmias, and even cardiovascular failure. These patients require emergency medical treatment.

Causes of a thyrotoxic crisis include:

• Certain medications
• Iodine supplementation or
• discontinuation of antithyroid therapy

Specialists in thyroid autonomy focus on human hormone balance and metabolism. For this reason, they are part of the fields of endocrinology and diabetology.

Depending on any comorbid conditions, pulmonology, cardiology, and other areas of internal medicine may also be important. Radiology plays a key role, particularly in diagnosis and radioiodine therapy.

What Is Thyroid Autonomy?

Thyroid autonomy refers to the loss of control of parts of the thyroid tissue by the thyrotropic regulatory loop. The affected areas produce thyroid hormones autonomously, that is, independently of TSH and the pituitary gland.

What is disseminated thyroid autonomy?

Disseminated thyroid autonomy is a multifocal form in which multiple autonomous areas are present within the tissue. This form can gradually lead to overt hyperthyroidism.

How does thyroid autonomy develop?

The most common cause of thyroid autonomy is iodine deficiency. Somatic heterozygous mutations in thyrocytes can lead to constitutive activation of the cAMP cascade, thereby stimulating growth and hormone production.

How is the diagnosis made?

Diagnosis involves measuring basal TSH as well as free T3 (ft3) and free T4 (ft4) to assess thyroid function. A scintigraphy allows for the localization of the autonomous tissue and shows the distribution of the autonomous areas.

How is thyroid autonomy treated

Treatment options include antithyroid medications, radioiodine therapy, or thyroid resection. The choice depends on the proportion of autonomous tissue, the patient’s age, and the clinical severity of hyperthyroidism.