Hyperthyroidism is a medical condition in which the thyroid gland becomes overactive, synthesizing too much hormones. It occurs when the thyroid releases too much of its hormones in the blood stream over a short (acute) or long (chronic) period of time, causing thyrotoxicosis. Thyroid hormone is important at a cellular level, affecting nearly every type of tissue in the body.
Thyroid hormone is critical to normal function of the cell as it functions as a stimulus to metabolism. In excess, it both overstimulates metabolism and exacerbates the effect of the sympathetic nervous system, causing "speeding up" of various body systems and symptoms resembling an overdose of epinephrine (adrenaline). These include fast heart beat and symptoms of palpitations, nervous system tremor and anxiety symptoms, digestive system hypermotility (diarrhea), and weight loss. On the other hand, a lack of functioning thyroid tissue results in a symptomatic lack of thyroid hormone, termed hypothyroidism.
Symptoms of hyperthyroidism include weight loss, increased heart rate, anxiety, hyperactivity, irritability, tremors, sweating, etc. The treatment depends on the cause and the severity of symptoms. It usually involves initial temporary use of suppressive thyrostatics medication, and possibly later use of permanent surgical or radioisotope therapy. All approaches may cause under active thyroid function (hypothyroidism) which is easily managed with levothyroxine supplementation.
Professor explains hyperthyroidism (video)