Hyperthyroidism (Overactive Thyroid)

What the thyroid does

The thyroid is a butterfly-shaped gland in the front of the neck. It makes the hormones thyroxine (T4) and triiodothyronine (T3), which set the speed of metabolism in almost every organ. The pituitary gland controls it by releasing thyroid-stimulating hormone (TSH). When thyroid hormone is high, TSH falls to very low levels, which is the key blood test finding.

Symptoms of hyperthyroidism

• weight loss despite eating normally or more
• fast heartbeat, palpitations or irregular rhythm
• nervousness, anxiety, irritability
• tremor of the hands
• feeling hot, sweating, heat intolerance
• trouble sleeping
• frequent bowel movements or diarrhea
• muscle weakness, especially of the thighs and upper arms
• tiredness
• light or infrequent periods, and reduced fertility
• thinning hair and fine, brittle nails
• a swollen neck (goiter)
• in Graves' disease: gritty, red or bulging eyes

Older adults may have few typical symptoms. They may instead have weight loss, fatigue, depression or atrial fibrillation, sometimes called "apathetic hyperthyroidism".

Causes

Diagnosis

1. TSH: low or undetectable.
2. Free T4 and T3: high. When TSH is low but T4 and T3 are normal, it is called subclinical hyperthyroidism.
3. Thyroid antibodies: TSH receptor antibodies (TRAb or TSI) confirm Graves' disease.
4. Radioactive iodine uptake and scan: high diffuse uptake in Graves', hot spots in nodules, low uptake in thyroiditis. Not done in pregnancy.
5. Thyroid ultrasound: for nodules and blood flow.
6. Other: ECG for heart rhythm, and bone density testing in older adults.

Treatment

Symptom control

Beta-blockers such as propranolol or atenolol quickly ease palpitations, tremor and anxiety while other treatments take effect.

Antithyroid medicines

• Methimazole is the first choice for most people. It reduces hormone production within weeks.
• Propylthiouracil (PTU) is preferred in the first trimester of pregnancy and in thyroid storm.
• Treatment for Graves' disease usually lasts 12 to 18 months; about a third to a half of patients stay in remission after stopping, and long-term low-dose treatment is another option.
• Side effects include rash and itching, and rarely liver injury or agranulocytosis (very low white cells), which causes fever and sore throat.

Radioactive iodine (RAI)

A capsule or liquid of iodine-131 is absorbed by thyroid cells and destroys them over 2 to 3 months. It is effective and widely used, but usually leads to an underactive thyroid requiring lifelong levothyroxine. It is not used in pregnancy or breastfeeding, and may worsen Graves' eye disease in some.

Surgery (thyroidectomy)

Removing all or most of the thyroid is chosen for large goiters, suspicious nodules, severe eye disease, pregnancy when medicines fail, or by preference. Lifelong thyroid hormone replacement follows. Risks include voice changes and low calcium from parathyroid injury.

Thyroiditis

Usually only beta-blockers are needed, as the overactive phase is temporary; antithyroid medicines do not help.

Complications

• Heart: atrial fibrillation, stroke, heart failure
• Bones: osteoporosis and fractures
• Thyroid eye disease: bulging eyes, double vision, rarely vision loss; smoking makes it worse
• Thyroid storm: a rare, life-threatening surge triggered by infection, surgery or stopping medicine
• Pregnancy: miscarriage, preterm birth and preeclampsia if uncontrolled

Living with hyperthyroidism

• Take medicines as prescribed and keep blood test appointments.
• Stop smoking, especially with Graves' disease.
• Avoid high-iodine supplements such as kelp.
• Get enough calcium and vitamin D.
• Tell your doctor if you are planning pregnancy.

Frequently asked questions

What are the first signs of hyperthyroidism?

Early signs often include a fast heartbeat, feeling anxious or irritable, trembling hands, sweating, feeling hot, trouble sleeping and weight loss despite a good appetite. Some people notice more frequent bowel movements, lighter periods or a swelling in the neck.

What causes hyperthyroidism?

The most common cause is Graves' disease, an autoimmune condition. Others include overactive thyroid nodules, toxic multinodular goiter, thyroiditis, too much thyroid medication and excess iodine. Blood tests and a thyroid scan identify the cause.

Can hyperthyroidism be cured?

Often, yes. Radioactive iodine or surgery permanently stops overactivity, though usually lifelong thyroid hormone tablets are then needed. Some people with Graves' disease achieve lasting remission after a course of antithyroid medicine. Thyroiditis usually resolves on its own.

What is the difference between hyperthyroidism and hypothyroidism?

Hyperthyroidism is an overactive thyroid making too much hormone, causing weight loss, a fast heart and heat intolerance. Hypothyroidism is an underactive thyroid making too little, causing tiredness, weight gain, cold intolerance and constipation. Treatment for one can lead to the other.

Can hyperthyroidism cause anxiety?

Yes. Excess thyroid hormone stimulates the nervous system, causing anxiety, nervousness, irritability, restlessness and trouble sleeping. These symptoms usually improve once thyroid levels are controlled. Beta-blockers help in the meantime.