Diagnosing Hyperthyroidism

The team of experts at NYU Langone’s Thyroid Unit works together to diagnose hyperthyroidism and to determine the most appropriate treatment for you. These experts include endocrinologists, who specialize in treating people with disorders of the endocrine system, as well as nuclear medicine specialists, who perform tests that help diagnose the condition.

Hyperthyroidism is a hormonal disorder that results in an overproduction of thyroid hormones. These include thyroxine, commonly known as T4, and triiodothyronine, which is known as T3. People with this condition are described as having an overactive thyroid. 

The thyroid is a butterfly-shaped gland located in the lower front area of the neck. The thyroid helps regulate body function, including metabolism, heart rate, and body temperature. If the thyroid is overactive, body processes can speed up. 

As a result, people with hyperthyroidism may experience sudden weight loss, increased appetite, or hair loss. They may also feel irritable or anxious and have trouble sleeping. 

Left untreated, hyperthyroidism can lead to potentially serious complications, such as an arrhythmia, which is a rapid or irregular heartbeat, and congestive heart failure. It’s important that you receive a diagnosis as soon as possible. 

Causes of Hyperthyroidism

Hyperthyroidism can affect anyone at any age, though it tends to occur more frequently in women in their 30s and 40s and in those who have a family history of autoimmune disease. There are several causes of hyperthyroidism, most commonly Graves’ disease.

Graves’ Disease

Graves’ disease is the most common cause of hyperthyroidism. Graves’ disease is an autoimmune disorder. In people who have Graves’ disease, the body’s immune system produces antibodies, or proteins, that attack the thyroid gland.

Antibodies are proteins that help identify and destroy foreign substances in the body, such as bacteria and viruses. However, they can also cause disease if they mistakenly attack organs, as they do in Graves’ disease. These antibodies, called thyroid-stimulating immunoglobulins, cause the thyroid gland to make too much thyroid hormone. 

People with Graves’ disease experience many of the same symptoms as those who have hyperthyroidism due to other causes. Some symptoms, however, are unique to Graves’ disease.

The thyroid is generally enlarged, called a goiter, and more vascular. Also, some people with Graves’ disease develop eye problems. Sometimes the tissue behind the eyes becomes inflamed and swells, causing the eyes to bulge. Others may complain of dry, scratchy eyes or double vision.

Sometimes people who have this condition experience reddening or thickening of the skin on the shins or tops of feet, due to the swelling of connective tissue that is also caused by the antibodies’ attack. 

Graves’ disease can spontaneously go into remission, which is when the signs and symptoms of the condition have disappeared. For most people, however, the disease requires long-term treatment. 

This condition affects both men and women and, occasionally, children. It’s most common in women in their 20s and 30s. People with the disease often have family members with autoimmune or thyroid conditions, although it is not completely understood why some people develop it and others don’t. 

Other Causes of Hyperthyroidism

Nodules, or lumps, in your thyroid can also cause hyperthyroidism. These nodules are very common by age 50 or 60 and, most of the time, have no effect on thyroid function.

Sometimes, however, one or more nodules can become overactive and produce excess thyroxine. These are called hyperfunctioning or “toxic” nodules. 

If you have several nodules in the thyroid, this is called a multinodular goiter. Goiter is the term used to describe an enlarged thyroid. If these nodules are associated with the excessive production of thyroid hormone, this is called toxic multinodular goiter. Overactive thyroid nodules are nearly always benign. 

Hyperthyroidism can also occur during an episode of thyroiditis, which is when an inflammatory problem in the thyroid gland triggers the release of stored thyroid hormone. Typically, this release can cause a person to develop acute thyrotoxicosis, which is when an excessive amount of thyroid hormones are present in the body. This is sometimes followed by hypothyroidism.

During an episode of thyroiditis, the hyperthyroidism phase causes the cells of the pituitary gland that produce thyroid-stimulating hormone, or TSH, to become temporarily dormant, leading to hypothyroidism. The thyroid cannot restart thyroxine production until these cells “wake up.”

Thyrotoxicosis and hypothyroidism related to thyroiditis can resolve without treatment. However, some people require treatment of these conditions. 

Thyrotoxicosis can also occur if you are receiving synthetic thyroxine treatment for hypothyroidism and the dosage is too high. In addition, people with a history of thyroid cancer are often treated with high doses of thyroid hormone for many years to suppress TSH, which stimulates thyroid tissue growth. Your doctor can adjust the dosage, which usually alleviates your symptoms.

Diagnostic Tests

NYU Langone doctors take several steps to accurately diagnose hyperthyroidism, beginning with a physical exam and blood testing. They may also recommend a radioactive iodine uptake test.

Physical Exam

Your doctor asks about your symptoms and looks for physical signs of hyperthyroidism, such as a rapid pulse, an irregular pulse, or an enlarged thyroid. He or she may also check to see if you have prominent or bulging eyes, a common symptom of Graves’ disease.

Blood Testing

A blood test is an effective way to test for an overactive thyroid. Doctors may test for several thyroid markers in the blood, including T4 and T3. However, the most sensitive indicator of an overactive thyroid is TSH, which is often the only marker necessary to make a diagnosis.

TSH is a hormone made in the pituitary gland that signals the thyroid to increase hormone production. In most people with an overactive thyroid, TSH is markedly low. This is because the concentration of thyroid hormone in the blood is excessively high, which the pituitary gland senses, causing it to consequently reduce the production of TSH. 

Your doctor may also test for thyroid-stimulating immunoglobulins, which stimulate the thyroid in people with Graves’ disease. The presence of thyroid-stimulating immunoglobulins in your blood, however, does not necessarily mean you have hyperthyroidism. 

Radioactive Iodine Uptake Test

If your endocrinologist suspects you have hyperthyroidism, he or she may recommend that you have a radioactive iodine uptake test. The results of this test give your doctor insight into how well your thyroid is functioning.

Before the scan, which is an outpatient procedure, you are given a small amount of radioactive iodine, which is in pill form and taken by mouth. Thyroid cells vigorously absorb iodine, because it is the main building block for thyroid hormone. After the iodine is ingested, measurements of the uptake of radioactive iodine by the thyroid gland are taken after 4 hours and once again after 24 hours. 

When the radioactive iodine reaches the thyroid gland, it gives off radiation signals. A special camera used during the scan detects these signals and takes pictures of the thyroid from different angles, revealing the size and shape of the gland. Thyroid function can be assessed based on how much radioactive iodine is absorbed by the thyroid and if it is evenly spread throughout the gland or concentrated in a nodule.

If the thyroid absorbs none or only small amounts of the iodine, you may have thyrotoxicosis, which results from inflammation of the thyroid gland due to thyroiditis. If your thyroid absorbs large amounts of iodine, you may have Graves’ disease. If overactive or toxic nodules are present, iodine uptake mainly occurs in the area of these nodules.

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