Definition and Symptoms of Hyperthyroidism

The thyroid gland is an endocrine (hormone-producing) gland that is located in the neck. The gland is divided into two halves, or lobes, and has an overall butterfly-like shape. The thyroid gland is responsible for the production of important metabolic hormones, including the so-called thyroid hormones. There are two thyroid hormones, sometimes called T3 and T4; T4 is also known as “thyroxine.” Both of these hormones are directly involved in the regulation of metabolism and energy usage in the body. In a condition called hyperthyroidism, the thyroid gland produces too much thyroxine. Blood tests of a patient with hyperthyroidism show elevated levels of thyroxine in the blood. In contrast, hypothyroidism is a separate condition in which thyroid hormone levels are too low. Hyperthyroidism is also sometimes referred to as “thyrotoxicosis.”Too much thyroid hormone in the body results in an increase in the metabolic rate. The symptoms that result are systemic, affecting the entire body, and the symptoms may vary from person to person. The more elevated the levels of thyroid hormone, the more severe the symptoms usually are. A person who has a sudden onset of hyperthyroidism will usually lose weight suddenly and without a known cause. As a person loses weight, their appetite may stay at the same level, or in some cases the appetite may increase. A higher-than-normal heart rate is also common in people with hyperthyroidism. A heart rate of greater than 100 beats per minute (bpm) is known as tachycardia. A person with tachycardia may feel as though their heart is racing. Arrhythmia, or abnormal heart rhythm, is also common in cases of hyperthyroidism. A person with hyperthyroidism may also feel nervous, irritable or anxious and have increased levels of nervous energy, or they may experience fatigue. Other potential symptoms of hyperthyroidism include sleep problems, more frequent bowel movements, tremor or shaking of the hands, sensitivity to temperature and muscle weakness. All of these symptoms are common in hyperthyroidism, but they are general and can be found in other conditions.

Some patients with hyperthyroidism may have an enlarged thyroid gland that is visible and palpable, that is, you can see and feel that it is enlarged in the neck. Rarely, a symptom called Graves’¬†ophthalmopathy¬†may occur. In Graves’¬†ophthalmopathy, the tissues behind the eye in the eye socket begin to swell. This swelling pushes the eyes further out of the orbit than they should be, resulting in eyes that bulge or bug out of the eye sockets. This does not occur in all patients with hyperthyroidism, but it is a classic symptom of the condition.

Some people with hyperthyroidism may have more pronounced symptoms than others. People who are older tend to have less pronounced symptoms, which can make diagnosis of the condition more difficult. People who are taking certain medications, especially beta blockers, may not experience as many symptoms of hyperthyroidism because their medication counteracts and masks some of the symptoms.


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