Hyperthyroidism is a metabolic disease with several underlying causes. In all cases, the thyroid gland, or part of it, overproduces the thyroid hormones responsible for regulating metabolism, resulting in an increased metabolic rate that is characterized by weight loss, anxiety, and the primary life-threatening symptom - heart arrhythmia and rapid heartrate.
The usual underlying cause is Graves' disease, an autoimmune disorder that causes antibodies to release too much of one of the hormones, thyroxin, as in response to an infection. However, an adenoma in the thyroid gland can also lead to overproduction of the hormone, as can inflammation of the thyroid gland.
Once suspected, the disease can easily be diagnosed with a blood test.
There are two types of treatment. The first is the use of drugs that interfere with the production of the hormone. However, as these have to be taken indefinitely, radiation treatment (such as the ingestion of radioactive iodine) is often used to destroy part of the gland. However, this treatment can often lead to the opposite condition - hypothyroidism.