Hypothyroidism is a problem in which the thyroid is underactive and is very common, especially among women. At least 10% of women in the United States have signs of hypothyroidism by the age of 50. The risk of hypothyroidism increases with age and at age 60, 17% of women and 8% of men have signs of hypothyroidism. The most common cause of hypothyroidism is an autoimmune problem (i.e. the body attacks specific parts of itself) called Hashimoto's thyroiditis or lymphocytic thyroiditis. In this disease, the body makes antithyroid antibodies that attack and destroy the thyroid. Another common cause of hypothyroidism is thyroid surgery. Removal of the whole thyroid gland (i.e. total thyroidectomy) will definitely cause hypothyroidism and up to 30 to 50% of patients having half of the thyroid removed (i.e. thyroid lobectomy) will develop hypothyroidism. By removing the thyroid, the patient can no longer make thyroid hormone.
Unless the patient is given thyroid hormone in pill form, they are by definition hypothyroid. Similarly, radioactive iodine ablation (RAI ablation) and anti-thyroid medications are designed to stop the thyroid from making thyroid hormone and will cause hypothyroidism. Other medications such as lithium (used for psychiatric diseases such as bipolar disorder) and amiodarone (used for certain irregular heart rhythms) can cause hypothyroidism.
Signs and Symptoms
Hypothyroidism can range from asymptomatic forms where the patient has no symptoms all the way to severe, life-threatening disease.
Symptoms associated with hypothyroidism include:
- Lack of energy or drive
- Daytime sleepiness
- Weight gain
- Water retention or bloating (also known as myxedema)
- Thinning hair
- Dry skin
- Difficulty concentrating
It is very important to keep in mind that the symptoms of hypothyroidism are non-specific and can be found with a number of other diseases. While these symptoms MAY be found in patients with hypothyroidism, the symptoms do not make the diagnosis. The diagnosis of hypothyroidism is made with blood tests and careful evaluation by an experienced physician.
A patient's history and physical exam are important factors in making the diagnosis of hypothyroidism. The important factors in a patient's history include a family history of hypothyroidism or autoimmune diseases, medications they take, and a personal history of radiation to the head, neck, or chest. Most patients will not have any signs or physical exam findings associated to hypothyroidism and the thyroid may feel normal. Blood tests are critical to confirming the diagnosis. Patients with hypothyroidism will usually have a high TSH and a lower than normal T4 and/or T3 level. In fact, some patients may have no symptoms at all, but blood tests that make the diagnosis of hypothyroidism.
Since hypothyroidism is a lack of thyroid hormone, the treatment is to give the patient thyroid hormone in pill form. Most commonly, patients are given T4 (Synthroid or levothyroxine). Thyroid hormone pills are essentially what the body normally produces, just in pill form. For this reason, there are minimal side effects or allergic reactions. However, patients may have symptoms if they are taking too much or too little thyroid hormone. These symptoms may be similar to the symptoms of hypothyroidism if they are taking too little or to hyperthyroidism if they are taking too much. It is critical for patients to work closely with an expert thyroidologist to determine the correct dose of thyroid hormone. The TSH level will be checked 4 to 6 weeks after starting to confirm that the patient is on the correct dose.
While most patients will do well on a weight-based dose (1.6 mcg/kg), the dose of thyroid hormone needed varies from patient to patient and may need to be adjusted every once in awhile by the physician.