Just as thyroid function can decline, it can also kick into overdrive, causing symptoms such as a racing heart, anxiety, irritability, difficulty sleeping, excess sweating, weight loss, and muscle weakness. (One cause of hyperthyroidism can also cause eye problems, such as grittiness and burning.) Less typical symptoms include tiredness and weight gain. “About one-quarter or more of people with hyperthyroidism gain weight,” Kovacs says, “because it stimulates your metabolism, but it also increases your appetite, and if you’re eating more than is countered by your increased metabolism, you’ll gain.”
As with hypothyroidism, the symptoms can be far less dramatic in older people than in younger people. “Someone may just feel that his or her heart is fluttering a little bit and have vague discomfort or muscle weakness,” Paul says. But, Prebtani says, “you can also get a new onset of an irregular heart rhythm or a worsening of an underlying heart condition—or heart failure.”
As with hypothyroidism, a TSH test can determine whether the thyroid is functioning normally. If it reveals the thyroid is overactive, your doctor will probably refer you to a specialist.
The first order of business is a careful history, including any family history of thyroid or autoimmune disease.
“Have they had a big dose of iodine recently? Do they eat a ton of kelp? Those things can cause hyperthyroidism in some people,” Opgenorth explains. (Thyroid cells, which are the only cells in the body that can absorb iodine, take up the nutrient to make thyroid hormone.) The same goes for contrast agents used in certain types of CT scans. Certain medications and supplements (for example, natural products containing desiccated thyroid) can also cause hyperthyroidism.
The next step is usually a nuclear medicine scan, which involves injecting a small amount of a radioactive substance that will be picked up by the thyroid, then taking images with a special camera to detect where the material accumulates. If the scan reveals the entire gland is overactive, “that’s Graves’ disease,” Kovacs says. In this autoimmune disease, the immune system makes antibodies that spur the overproduction of thyroid hormone. “If it’s patchy, with over- and underactive nodules, that’s multinodular goitre, which is more common as we get older. Or is there a single ‘hot’ nodule?” (Nodules are small growths or lumps of abnormal thyroid tissue.) More rarely, “you don’t see the thyroid at all, because it’s not functioning and it has dumped all the thyroid hormone it made previously,” Kovacs says. This can occur when thyroid tissue becomes inflamed—a condition known as thyroiditis—due to a viral infection, for example.
“Treatment for overactive thyroid depends on the cause,” as well as the severity, Prebtani says. “Sometimes, if it’s mild, we might just wait and watch; some of these things, such as a case of thyroiditis, might resolve on their own.”
For Graves’ disease or overactive nodules, medication—typically a drug called Tapazole—is one option. “Generally, we start with that in everybody to bring the thyroid under control, regardless of the cause,” Kovacs says. (Other medications, such as beta blockers, are sometimes used in the interim to help control symptoms such as rapid heart rate.) “That can safely be used indefinitely. It’s not curing the problem, but it puts the brakes on the situation.”
For hot nodules, that therapy would need to continue lifelong, while with Graves’ disease, “if you bring it under control, you’ll need a lower and lower dose after a while,” Kovacs says. In some cases, the condition goes into remission for long periods when the immune system “forgets” about the thyroid, during which time the medication can be stopped.
Using a small dose of radioactive iodine to burn out overactive thyroid tissue is another possible solution. In the case of a single spot of overactive tissue in a gland that’s otherwise suppressed, sometimes “the radioactive iodine knocks out the hot nodule, the rest of the thyroid isn’t touched, the thyroid wakes up, and you’re fine,” Kovacs says. “But you still run the risk that the whole thyroid will get knocked out.” (Either of these outcomes can also occur after surgery to remove the abnormal tissue.) The latter scenario is also often the result when radioactive iodine is used to treat Graves’ disease, and in both situations, the person is rendered hypothyroid and must take thyroid hormone for the rest of his or her life.
The potential problem here, Kovacs says, is that “you run the risk that you’ll be in that 20 to 30 per cent of people who never feel the same again. So for most patients, I tend to recommend the route of the Tapazole, unless there’s a problem—for example, if they never get good control with medication.”
Linda Rooker ended up suffering a rare life-threatening health crisis called “thyroid storm” before being diagnosed with Graves’ disease and ultimately decided on radioactive iodine. Since that procedure burned out her thyroid, she had to start taking thyroid hormone; it took a year to get the dosage right, but she’s been feeling well ever since.