Hyperthyroidism, also known as overactive thyroid, is caused by an overproduction of thyroid hormones. Unfortunately, the thyroid gland is complex, and the signs and symptoms of hyperthyroidism can resemble those of other health problems, making the condition difficult to diagnose.
Minor fluctuations in thyroid hormones can be normal. For example, your thyroid may release more thyroxine (thyroid hormone) to help you stay warm when your body temperature drops. You may also experience an increase in thyroid hormone production during pregnancy. But these kinds of variations aren’t typically enough to send your thyroid into overdrive.
Hyperthyroidism, or overactive thyroid, is a medical condition that occurs when the thyroid gland chronically produces too much thyroid hormone.
You may not know you have hyperthyroidism until your doctor detects abnormal levels of thyroid hormones in your annual blood work. But in some cases, you may be able to tell something isn’t right based on unusual symptoms you might experience, including the following:
Sudden, unintentional weight loss
Increased appetite
Nervousness or anxiety
Pounding, rapid, or irregular heartbeat
Tremors (especially in your hands)
Sweating
Difficulty sleeping
Sensitivity to heat
Hair loss
Brittle, thinning hair
Thinning skin
Muscle weakness
More frequent bowel movements
Missed menstrual periods or changes in menstrual patterns
Bulging eyes, sensitivity to light, or blurry vision (in people with Graves’ ophthalmopathy)
“The most common symptoms are heart palpitations, weight loss, diarrhea, heat intolerance, feeling shaky, and trouble sleeping,” says Gregory Dodell, MD, an assistant clinical professor of medicine, endocrinology, diabetes, and bone disease at the Icahn School of Medicine at Mount Sinai in New York City. “It can also disrupt the menstrual cycle and cause hair thinning.”
Often, people with hyperthyroidism think they’re just nervous or stressed. Meanwhile, older adults and those taking medicines known as beta-blockers are less likely than other people with hyperthyroidism to experience its telltale signs.
Hyperthyroidism progresses at different rates in different people depending on the cause. For example, in older people with toxic nodules (lumps in the thyroid that produce excess thyroid hormone), it may take years to cause health risks. In younger people with Graves' disease, it can occasionally progress very rapidly and can even develop into a life threatening condition called thyroid storm.
Graves’ ophthalmopathy (also known as thyroid eye disease) is a symptom of Graves’ disease, an autoimmune condition that causes hyperthyroidism. The distinctive bulging of the eyes associated with Graves’ ophthalmopathy, however, isn’t as common as many people believe.
“Not all patients with hyperthyroidism develop eye manifestations,” says Dr. Dodell. Figures vary, with some research noting that 25 to 50 percent of people with Graves’ disease experience ophthalmic manifestations, while Dodell says that in his personal experience, the incidence is about 10 to 20 percent. Other eye symptoms of Graves’ disease include redness and irritation, double vision, and light sensitivity. Graves’ ophthalmopathy is more common in hyperthyroid patients who also smoke.
There are also some similarities between hyperthyroidism and hypothyroidism, or underactive thyroid, including menstrual cycle disruptions, fatigue, hair changes, and mood changes, according to Dodell. Still, hypothyroidism generally causes opposite symptoms, such as cold intolerance and unintentional weight gain. The only way to really know whether you have a thyroid issue is to get the right tests to check your hormone levels.
Hyperthyroidism is sometimes discovered during an annual physical. Other patients may specifically see their doctor if they start experiencing any of the above symptoms, especially rapid heartbeat and unintentional weight loss.
Sometimes these symptoms may be related to an entirely separate health condition, so it’s important to see your doctor to rule these out. To check for hyperthyroidism, your doctor may perform any of the following procedures.
Physical Exam
Your doctor will examine your thyroid gland as you swallow, to determine whether it’s enlarged, tender, or bumpy. Your doctor may also check for tremors in your hands, overactive reflexes, changes in your eyes, a rapid heartbeat, or warm and moist skin.
Blood Test
Blood tests that measure levels of thyroxine and triiodothyronine (hormones made by the thyroid gland) and thyroid-stimulating hormone (TSH), among other labs, may be used to diagnose hyperthyroidism.
The first step is to measure TSH levels. TSH is produced by the pituitary gland in your brain, which sends signals to the thyroid gland to make hormones. It’s a negative feedback loop: Typically, a low TSH level implies your thyroid gland is releasing too much thyroxine, which is suppressing pituitary TSH secretion and causing what’s called primary hyperthyroidism. This response may be due to excess thyroid hormones in the body, which may indicate that your thyroid is overactive. TSH is especially important to measure in people who don’t necessarily have the classic symptoms of hyperthyroidism.
After TSH is measured, your doctor will check other thyroid hormone levels. These blood tests are often ordered all at the same time for convenience. If you have hyperthyroidism, you will likely have elevated thyroxine (T4) or triiodothyronine (T3) coupled with low TSH levels.
Sometimes elevated total T4 levels are caused by medications you take, including oral contraceptives. Pregnancy can also cause elevated T4 because of the boost in estrogen. On the flip side, corticosteroids and severe illnesses can lower T4 levels. This is why it’s important for your doctor to look at all the related thyroid hormones to get a full picture of what’s going on with your thyroid gland.
There’s also a blood test that measures thyroid antibodies, which is helpful in diagnosing the autoimmune disorder Graves’ disease. The presence of thyroid antibodies in your blood work may indicate that your immune system is attacking the thyroid by mistake.
Radioactive Iodine Uptake Test
This test is used to determine what’s causing your hyperthyroidism. It checks how much iodine your thyroid gland absorbs, which in turn can help diagnose the cause of why the gland is overactive.
For this test, you swallow a small dose of radioactive iodine and have your thyroid gland scanned, typically 6 hours or 24 hours later. This painless scan is completed using a device called a gamma probe, which is positioned on the outside of your neck to measure the amount of radioactivity in your thyroid gland.
A high uptake of radioactive iodine suggests that your thyroid gland is producing too much thyroxine, likely due to Graves’ disease or hyperfunctioning thyroid nodules (lumps on the thyroid that can release thyroid hormones).
If your radioactive iodine uptake is low and your TSH is low, you may be diagnosed with thyroiditis, inflammation of the thyroid that results in a release of thyroid hormone caused either by antibodies, medication, or a virus rather than an overproduction of thyroid hormone in the thyroid.
Thyroid Scan
This test takes a picture of your thyroid gland to determine its size, shape, and position. It can help doctors find the cause of hyperthyroidism and check for thyroid nodules.
“Hyperthyroidism can be caused by what we call a hot nodule, a nodule that’s over-secreting thyroid hormone,” says Dodell. Multiple toxic nodules may also be present. “These areas will be demonstrated on the scan,” he says.
A radioactive isotope is swallowed via a liquid or capsule. A special camera then produces an image of your thyroid gland on a computer screen. Sometimes, doctors perform a thyroid scan and a radioactive iodine uptake test at the same time.
Other Scans
Your doctor may perform other scans, such as a thyroid ultrasound (the latter is commonly used), to get a better view of your thyroid gland or examine a large goiter.
Often, the thyroid gland will have nodules or bumps. Depending on the size and other characteristics of the nodule(s), your doctor may recommend a biopsy. For the biopsy, the doctor will place a needle into the nodule with the guidance of the ultrasound. The sample is then sent to the lab to test for cancer. Thyroid nodules that are causing hyperthyroidism aren’t usually cancerous.
While it can take time to diagnose hyperthyroidism, it’s important to follow through with all the recommended tests your doctor orders to help determine the exact cause of an overactive thyroid gland so you can start effective treatment.
Because the thyroid gland is complex, and the signs and symptoms of hyperthyroidism can resemble those of other health problems, the condition can be difficult to diagnose.
The most common symptoms of hyperthyroidism include heart palpitations, weight loss, diarrhea, heat intolerance, shakiness, trouble sleeping, menstrual cycle disruption, and hair thinning.
While hyperthyroidism can be diagnosed in an annual physical via a thyroid gland exam and blood test, a number of other tests, including a radioactive iodine uptake test, thyroid scan, ultrasound, and biopsy can help your doctor make a proper diagnosis.
If you’re navigating hyperthyroidism, it’s important to stay patient and follow through with all the recommended tests your doctor orders to determine the exact cause of your overactive thyroid gland and devise an effective treatment plan.
