What is Hyperthyroidism?
Hyperthyroidism is a medical condition characterized by hyper-activation of the thyroid gland and release of excess thyroid hormone. The thyroid gland plays a critical role in the body’s metabolism – excess thyroid hormone results in an increased metabolic rate. This leads to features such as anxiety-agitation, palpitations, tremor, weight loss, sensitivity to heat, insomnia, increased heart rate (tachycardia), and diarrhea. Serious long-term effects may include osteoporosis, cardiac arrhythmias, and heart failure.
Graves’ disease is the most common form of hyperthyroidism and is characterized by exophthalmos (bulging of the eyes), periorbital and conjunctival edema, impaired eye movement, and pretibial myxedema. It is caused by autoantibodies against the TSH receptor on the thyroid gland, which results in a goiter and increased thyroid hormone release.
What Causes Hyperthyroidism?
TSH is released by the anterior pituitary, which is located underneath the brain in a region called the Sella turcica. TSH then enters the blood stream and acts on TSH receptors on the thyroid gland – this stimulates the thyroid gland to release more thyroid hormone (T4).
Under normal conditions, high T4 levels feedback to the pituitary gland and signal the gland to stop releasing TSH. With less TSH stimulation, the thyroid secretes less T4.
Grave’s disease is the most common form of hyperthyroidism. In Graves’ disease, autoantibodies are formed against TSH receptors on the thyroid gland, which activate the thyroid. This results in growth of the thyroid gland (goiter) and stimulation of thyroid hormone synthesis and secretion. The normal feedback system no longer functions in this disease.
Thyroid hormone is a major hormone that regulates the metabolic rate – increased thyroid hormone activates metabolism and leads to weight loss, increased heart rate, heat intolerance, and palpitations.
How Common is Hyperthyroidism?
Hyperthyroidism is common in the United States and responsible for a relatively large percentage of primary care visits. The most common cause is Graves’ disease, an autoimmune disease that results in activation of the thyroid gland. The condition often requires referral to an endocrinology and sometimes ophthalmology specialist.
Hyperthyroidism is more common in women than men and Graves’ disease is more common in younger women than older women. The incidence of Graves’ disease is about 4.6 per 1000 during 10 years of observation. The prevalence of hyperthyroidism is about 1.3% and rises to approximately 5% in women of advanced age. These older women more commonly have toxic multinodular goiter.
Signs and Symptoms
Symptoms and signs of hyperthyroidism often include:
- Shortness of breath
- Tremor (shaking)
- Unintentional weight loss
- Sensitivity to heat (heat intolerance)
- Insomnia (trouble sleeping)
- Increased heart rate (tachycardia)
- Diarrhea – increased bowel movements
Severe long term effects of hyperthyroidism may consist of osteoporosis, cardiac arrhythmias, and heart failure.
Graves’ disease is the most common form of hyperthyroidism – it is characterized by:
- Exophthalmos (bulging of the eyes)
- Periorbital and conjunctival swelling
- Impaired eye movement
- Pretibial myxedema (lower extremity swelling)
If you have exophthalmos, you might have a positive lid lag sign. Your doctor will evaluate for this by having you follow their finger up and down –lid lag is present if your sclera can be seen above the iris as you look downward.
The diagnosis of hyperthyroidism is suggested based on symptoms and physical examination, but typically confirmed with a thyroid stimulating hormone (TSH) test that is low and a free T4 level that is high.
If you are not pregnant, your doctor will likely check your blood for thyrotropin receptor antibodies and order a radioactive iodine uptake test. They may also check for thyroidal blood flow on ultrasonography to distinguish Graves' disease from other causes of hyperthyroidism. Pregnancy and breastfeeding are contraindications for radionuclide imaging.
Your doctor may also check basic blood tests including a CMP (comprehensive metabolic panel) and CBC (complete blood cell count), as well as a urine drug screen.
If your heart rate is elevated, your doctor will likely obtain EKG (electrocardiogram). If you have signs of heart failure they may also order a chest x-ray and ultrasound of the heart (echocardiogram).
Hyperthyroidism Medication and Treatment
Symptoms of Graves’ disease are typically treated with beta-blockers such as Tenormin (atenolol). This is used to decrease thyroid hormone synthesis and ameliorate symptoms of hyperthyroidism.
Definitive treatment of hyperthyroidism requires radioiodine ablation or surgery.
- Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis. Thyroid 2016; 26:1343. - https://www.ncbi.nlm.nih.gov/pubmed/27521067
- Singer PA, Cooper DS, Levy EG, et al. Treatment guidelines for patients with hyperthyroidism and hypothyroidism. Standards of Care Committee, American Thyroid Association. JAMA 1995; 273:808. - https://jamanetwork.com/journals/jama/article-abstract/389711
The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.