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Overactive thyroid (or hyperthyroidism) is a fairly common condition caused by excess thyroid hormone, which leads to symptoms of hyperexcitation such as tremor and rapid heartbeat. While severe cases can be dangerous, most are mild and relatively simple to treat.
What is hyperthyroidism?
The thyroid is a small, bow-tie shaped gland in your neck. Its main job is to produce thyroid hormone (known as T3 or T4), which serves a wide array of functions throughout the body.
When too much thyroid hormone is released, the body’s metabolism gets ramped up, causing symptoms such as tremor, sweating, unintentional weight loss, and an accelerated heartbeat.
The most common cause of hyperthyroidism is an autoimmune condition known as Graves’ disease, where the body mistakenly attacks its own thyroid causing the gland to over-activate.
While severe hyperthyroidism (known as thyroid storm) can be deadly, most cases are mild and entirely manageable.
You should visit your primary care physician, who might take a blood test to measure your levels of thyroid hormone. The test will tell the doctor whether a referral to an endocrinologist is useful. Treatment plans would likely be set by the specialist and include drugs to reduce your thyroid activation.
Symptoms of hyperthyroidism
The main symptoms of hyperthyroidism, known collectively as thyrotoxicosis, are seen in all kinds of thyroid hormone excess regardless of the specific cause. Generally speaking, hyperthyroidism resembles a state of overactivation or “ramping up” of the body’s metabolism and energy consumptive processes. This overexcitation may be mild enough to go unnoticed. When symptoms do present, they commonly include the following.
- Unintentional weight loss
- Palpitations: This is a rapid or irregular heartbeat.
- Irritability, agitation or mood swings
- Insomnia or restlessness
- Heat intolerance: This refers to excess sweating and uncomfortable warmth in relatively normal ambient temperatures.
- Skin irritation such as clammy or itchy skin
While not seen in all cases of hyperthyroidism, many forms can cause enlargement of the thyroid gland itself. This results in swelling at the front of the neck known as a goiter.
Eye and skin symptoms unique to Graves’ disease
While most symptoms of hyperthyroidism occur equally regardless of the specific cause, there are two important symptoms seen only in Graves’ disease. These involve specific changes in the eyes and the skin which are caused directly by the Graves’ disease autoantibodies, meaning they’re not seen in other causes of thyroid hormone excess.
Graves’ disease causes a specific and unique bulging of the eyes variously referred to as either Graves’ ophthalmopathy, Graves’ orbitopathy, exophthalmos or proptosis. The antibodies responsible for over-stimulating the thyroid in Graves’ disease also cause the tissues around the eyeball to swell, pushing the eye forward and giving a bulging or bug-eyed appearance. This distinctive appearance is often the most recognizable feature of Graves’ disease. Along with the protruding appearance, other symptoms associated with Graves’ ophthalmopathy include the following.
- Blurry vision
- Double vision
- Dry eyes: Often described as a gritty or sandy feeling
- Light sensitivity
- Painful or impaired eye motion: This is usually a sign of advanced disease-causing compression of the eye muscles.
Graves’ disease also causes a set of specific skin changes known as pretibial myxedema or thyroid dermopathy. The most common location is over the shins, where it causes the skin to appear raised, darkened, and purple or otherwise discolored. Occasionally other areas can be involved as well such as the feet or arms.
What causes hyperthyroidism?
The most common cause of hyperthyroidism is known as Graves’ disease. It is an autoimmune condition, meaning that the body mistakenly attacks its own thyroid. In the case of Graves’, the antibodies which carry out this attack also activate the thyroid causing it to produce too much thyroid hormone. It’s not clear what causes a given person to develop Graves’ disease, but family or personal history of autoimmune disease is a known risk factor. It is also more common in women and those over 60 years old. Less common causes of hyperthyroidism include the following.
- Thyroid nodules: This is a type of noncancerous overgrowth of thyroid tissue which sometimes produces thyroid hormone.
- Viral thyroiditis: This is where an infection damages the thyroid gland causing the temporary release of large amounts of stored thyroid hormone.
- Autoimmune thyroiditis: This causes a similar spillage of thyroid hormone, particularly during or shortly after pregnancy.
- Taking excess thyroid hormone or weight loss supplements: These sometimes contain thyroid hormone in a dangerous attempt to boost their efficacy.
- Rare forms of cancer: Involving the thyroid, testicles or ovaries
- Excess iodine: This can be found in food or medications such as amiodarone, though this is very rare and usually requires a pre-existing thyroid problem.
Treatment options and prevention for hyperthyroidism
Treatment of hyperthyroidism generally falls into three categories: blocking the effects of thyroid hormone with antithyroid medications, destroying (“ablating”) the overactive thyroid gland using radioactive iodine, and surgically removing overactive thyroid tissue.
The preferred treatment varies depending on the cause and specific circumstances of a given individual’s hyperthyroidism, so it is important to review the options with your doctor. Broadly speaking, antithyroid medications have the advantage of being non-invasive and reversible. Both surgery and radioactive iodine offer more permanent solutions but tend to disrupt normal thyroid function, leading to the need for lifelong thyroid hormone supplementation.
The two main antithyroid medications are methimazole (Tapazole) and propylthiouracil (PTU). While both are effective at suppressing the excess thyroid hormone, methimazole is generally preferred since it is less likely to cause troublesome side effects, particularly liver damage.
- For those who are pregnant: Both medications can be problematic during pregnancy, so any woman with hyperthyroidism who is pregnant or may become pregnant should make sure their doctor knows about any possibility of pregnancy.
- For those with Graves' disease: In about one in four people with Graves’ disease, a year-long course of antithyroid medication is sufficient to provide long-term resolution of symptoms. However, many people will eventually need more definitive treatments such as radioactive ablation or surgical resection.
In addition to blocking thyroid hormone itself, treatment of thyrotoxicosis often involves blocking the adrenaline (also known as epinephrine) that is released in hyperthyroidism. This is done with beta-blocker medications such as propranolol (Inderal) which help control the elevated heart rate, high blood pressure and tremors caused by the excess adrenaline seen in hyperthyroidism.
Radioactive iodine ablation
When iodine supplements are taken by mouth, the absorbed iodine deposits primarily in the thyroid where it plays an important role in thyroid hormone production. When radioactive iodine is taken, the thyroid takes it up just like it would normal iodine. This makes radioactive iodine extremely useful in both the diagnosis and treatment of hyperthyroidism. When taken over several months, radioactive iodine becomes concentrated in overactive thyroid cells, causing them to slowly shrink and die off. Radioactive iodine that is not absorbed is flushed from the body without harming other healthy tissues.
- Risks for those who are pregnant: It can be harmful to a growing fetus or newborn and is therefore not appropriate for women who are pregnant or breastfeeding.
- Risk of exacerbating your condition: It can also cause the dying cells to release their stored thyroid hormone. This can temporarily worsen hyperthyroidism, so radioactive iodine is often used after a course of antithyroid medications have been given to “cool down” the overactive thyroid.
- Additional supplementation: Radioactive iodine ablation is often so effective that it decreases thyroid activity below normal levels, requiring lifelong thyroid hormone supplementation. This is relatively simple and inexpensive but does mean taking a pill every day for the rest of one’s life.
One definitive way to cure almost any case of hyperthyroidism is to simply remove the thyroid gland. This is done with a relatively simple surgical procedure known as a thyroidectomy. In some cases, it is only necessary to remove part of the thyroid gland, known as a partial or subtotal thyroidectomy. These surgeries are generally well-tolerated with a low risk of side effects, making them an appealing option for many people.
- Risk of damage to parathyroid glands: The most common complication is damage to the nearby parathyroid glands, which can lead to significant abnormalities in the body’s calcium levels.
- Additional supplementation: Similar to radioactive ablation, thyroidectomy removes the natural source of thyroid hormone meaning that you would need to take supplemental thyroid hormone by mouth for the rest of your life.
For most people, there is little that can be done to prevent the development of hyperthyroidism.
- Sporadic cases: Most cases are considered sporadic, meaning that they occur unexpectedly without an obvious trigger.
- Potentially preventable cases: Several specific causes could potentially be avoided such as pregnancy or overconsumption of thyroid hormone supplements.
- Not preventable cases: For most people whose overactive thyroid is caused by autoimmune disease such as Graves’, viral infection or overgrown thyroid nodules, there is not much to be done to prevent the condition.
However, one thing that can be done is to avoid tobacco products. Not smoking is good advice for anyone, but it is particularly important for people living with Graves’ disease. Studies have found that eye symptoms are significantly more common in those with Graves’ disease who also smoke. This may be partially due to the direct irritation smoke causes to the eyes, which in Graves’ disease are often protruding past their protective eyelids. That said, smoking appears to not only worsen irritation but actually contribute to the development of tissue swelling seen in Graves’ ophthalmopathy. Since Graves’ disease is the most common cause of hyperthyroidism, anyone with an overactive thyroid should try particularly hard to avoid smoking. Protecting the eyes with glasses can also help reduce irritation.
When to seek further consultation for hyperthyroidism
While most cases of an overactive thyroid are mild and can be managed at your convenience, it is always safer to seek professional medical assistance if you are concerned about symptoms you are experiencing. Specific symptoms that merit seeking medical attention sooner rather than later include the following .
- Racing or irregular heartbeat
- Swelling of the neck, particularly if it impairs swallowing or breathing
- Significant, unexplained weight loss
- Vision loss or significant eye pain
If you are concerned about any of these symptoms and unable to reach your doctor, the safest thing would be to call an ambulance or seek urgent attention at your local emergency department.
Once you’ve begun treatment for hyperthyroidism, it is important to follow up regularly with your doctor. Your symptoms should improve with treatment. New or significantly worsening symptoms would be a good reason to contact your physician.
Questions your doctor may ask to determine overactive thyroid
- Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
- Do you have trouble sleeping?
- Have you had any changes in your weight?
- When was your last menstrual period?
- Are you having difficulty concentrating or thinking through daily activities?
Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.
Dr. Kelly is a graduate of the University of Pennsylvania Perelman School of Medicine, specializing in internal medicine and bioethics. He received his undergraduate degree from Emory University with a BA in Spanish. Dr. Kelly has formal training in medical interpretation and translation, along with several years of professional experience in medical communication and editing work for publication.
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- Hyperthyroidism - Symptoms & Causes. The Mayo Clinic. Updated Nov. 3, 2018. Mayo Clinic Link