Hyperthyroidism: When Your Thyroid Gland Goes Into Overdrive

By Tracy Tylee, MD

You feel tired. You’re having trouble sleeping. Your heart is racing, and you feel shaky day and night. You’re under a lot of stress, which might explain these symptoms. Or could it be something else…like a thyroid issue? Most of us who are knowledgeable about the topic of thyroid disease typically think of hypothyroidism, or low thyroid function, which can cause fatigue, difficulty concentrating and weight gain. However, fatigue and feelings of anxiety can also be symptoms of hyperthyroidism, or too much thyroid hormone. Recognizing these symptoms is important, as nearly all causes of hyperthyroidism require treatment to prevent long-term complications.

Just how much of a problem is hyperthyroidism?

Hyperthyroidism is less common than hypothyroidism, affecting about 1.2 percent of the United States population, compared to 5 percent affected with hypothyroidism. Like most thyroid disease, it is more common in women, and its incidence increases with age.

What symptoms does hyperthyroidism cause?

Thyroid hormone sets the pace for the body’s metabolism, the process by which cells turn nutrients into energy to enable your body tissues to function properly, so having too much thyroid hormone causes symptoms of an overactive metabolism. Persons with hyperthyroidism often experience weight loss despite an increased appetite, feel hot when others are not, have tremors, anxiety and fatigue. You might have difficulty sleeping. Or your bowels can be overactive, leading to frequent bowel movements. The eyes can also be affected with double vision or eye inflammation and pain when the patient has an autoimmune condition called Graves’ disease, which occurs when the immune system launches an attack on the thyroid.

Hyperthyroidism symptoms may be mild in their presentation or can be quite debilitating, particularly in older individuals where unexplained weight loss is often the only symptom. Many people may attribute their symptoms to stress, anxiety or even the normal aging process. However, it’s important to recognize the possibility of thyroid disease, as there are longterm complications arising from untreated hyperthyroidism. Older individuals with hyperthyroidism have a three-fold greater risk of atrial fibrillation, an irregular heart rate that increases the risk of stroke, compared to patients with normal thyroid function. Hyperthyroidism also increases the risk of osteoporosis and fracture. Treatment of hyperthyroidism can help prevent these serious complications.

How does hyperthyroidism develop?

Hyperthyroidism is due to too much thyroid hormone circulating in the blood. Normally, the amount of thyroid hormone in your system is controlled by the pituitary gland, a pea-sized structure located at the base of the brain. The pituitary gland produces a hormone called thyroid stimulating hormone (TSH), which travels through your bloodstream to the thyroid gland where it binds to receptors (a molecule that receives a thyroid hormone and permits it to dock on the nuclear membrane of a cell) and stimulates the thyroid to make thyroid hormone. Normally, when thyroid levels are high, the pituitary gland decreases production of TSH to reduce stimulation of the thyroid and return hormone levels to normal. Similarly, if thyroid hormone levels are low, the pituitary’s output of TSH will increase to stimulate the thyroid gland to produce more hormone (See Figure 1).

In hyperthyroidism, this system goes awry due to a number of causes. The most common cause of hyperthyroidism is Graves’ disease, in which your body produces antibodies that stimulate the TSH receptor on the thyroid gland. The thyroid can’t tell the difference between TSH and the TSH receptor antibodies, so it “thinks” the pituitary is directing the thyroid to make more hormone and the thyroid complies. Patients with Graves’ disease will often have an enlarged thyroid, also called a goiter, due to the increased stimulation of the thyroid gland.

Sometimes patients will have thyroid nodules that are producing thyroid hormone independent of TSH stimulation. This is more common for patients from iodine-deficient geographic areas, but it occurs worldwide.

Inflammation of the thyroid gland can also cause hyperthyroidism. This can occur following a viral infection, after pregnancy, or due to certain medications. In this situation, the inflammation damages the thyroid cells. Normally, the thyroid has large stores of pre-made thyroid hormone waiting to be released. When the cells are damaged, this hormone can leak out and lead to hyperthyroidism. This condition is usually only temporary – once the thyroid heals, the thyroid hormone stops leaking and levels return to normal within several months.

An important cause of hyperthyroidism is medication. Some weight-loss supplements may contain thyroid hormone components and can cause hyperthyroidism. If too little thyroid hormone causes weight gain and fatigue, it seems reasonable to assume too much thyroid hormone would cause weight loss and increased energy. Unfortunately, it doesn’t work that way. Too much thyroid hormone in the body can cause weakness due to loss of muscle mass, fatigue and other significant medical problems. Plus, excessive amounts of thyroid hormone can increase appetite, which is another reason it’s not a good weightloss tool. It is important to review any supplements you are taking with your physician to ensure you’re taking something that could be causing the problem or making your condition worse.

How is hyperthyroidism diagnosed?

When hyperthyroidism is suspected, a diagnosis is made through a simple blood test to measure both thyroid hormone levels and TSH. In most cases of hyperthyroidism, the TSH will be low as the pituitary is trying to decrease thyroid hormone production in response to the high levels of thyroid hormone in the body. The TSH is the most sensitive test available for measuring thyroid function, and in hyperthyroidism this may be low, even with thyroid hormone levels still in the normal range.

Once the blood test confirms the diagnosis of hyperthyroidism, additional tests may be needed to identify the underlying cause. In Graves’ disease, TSH receptor antibodies can be measured. Imaging studies are also helpful. One test, called a radioactive iodine scan, uses a small, harmless dose of radioactive iodine to help identify where excess thyroid hormone is being produced (thyroid cells are the main cells in the body that can absorb iodine). The thyroid uses iodine in the production of thyroid hormone, so if there is excess hormone production, such as in Graves’ disease, or the result of a hyperfunctioning nodule, a non-cancerous nodule growing in the thyroid that causes it to produce too many hormones, this area will “light up” on the scan. Conversely, if there is release of hormone stores rather than increased production, as occurs with inflammation of the thyroid, there will be low iodine uptake.

Thyroid ultrasound can also be helpful in identifying nodules. This procedure uses high-frequency sound waves that pass through the skin and are reflected back to the ultrasound machine, creating detailed images of the thyroid. An ultrasound is usually not necessary when the thyroid is overactive unless a nodule is apparent on physical examination and a nuclear medicine scan indicates that it is “cold,” which indicates the nodule is composed of cells that don’t make thyroid hormone. A nodule that is producing too much hormone will show up darker on the scan and is called “hot.”

Review of your medications with your provider is very important to make sure you are not taking excess thyroid hormone or other supplements that could cause hyperthyroidism.

What are my treatment options?

The treatment of hyperthyroidism depends on the underlying cause. If the thyroid is producing too much hormone, which occurs with Graves’ disease or hyperfunctioning nodules, thyroid hormone production can be blocked. There are several ways of doing this. The first is with a class of medications called thionamides. In the U.S., a thionamide called methimazole is commonly used, which blocks a step in the formation of thyroid hormone. The methimazole is typically taken once a day, initially at high doses, but the dose can be decreased as thyroid hormone levels return to normal. Methimazole can sometimes cause a rash, but is usually well tolerated. There are some rare but serious side effects, including liver injury or failure, which occurs in roughly one out of every 10,000 adults taking the medication, and suppression of the immune system, which can lead to potentially life-threatening infections, so your doctor will want to make sure you are aware of symptoms to look for.

Some individuals prefer a more definitive treatment, which can be accomplished with radioactive iodine or surgery. With radioactive iodine, commonly referred to as “thyroid ablation,” the patient is given a higher dose of radioactive iodine than what is used for a diagnostic scan. This will damage the thyroid cells and prevent them from being able to make thyroid hormone. This approach works well for hyperfunctioning nodules, as often only the nodule is damaged and the remaining thyroid gland retains normal function. In Graves’ disease however, since the entire gland is overactive, the patient will often become hypothyroid following treatment and require thyroid hormone replacement medication. Surgery, often reserved for those unable to take methimazole or radioiodine, is another option. If the thyroid gland is removed, there is no other internal source of thyroid hormone, so after surgery, the patient will be hypothyroid and require lifetime thyroid hormone replacement.

Hyperthyroidism due to thyroid inflammation is self-limited, meaning it will get better on its own. No specific treatment for this is needed.

What is the take-home message?

Stress and anxiety are common in modern day society. We often find ourselves having trouble sleeping, which can cause fatigue. However, when this is accompanied by other unexplained symptoms such as palpitations and tremor, or weight loss, the possibility of hyperthyroidism should be considered. While thyroid hormone is essential for normal metabolism, like anything, it is possible to have too much of a good thing.