What is an overactive thyroid?
An overactive thyroid occurs when the thyroid gland produces excessive amounts of thyroid hormone, which then over-stimulates our metabolic functions. In this situation you are said to be ‘hyperthyroid’.
Symptoms of hyperthyroidism
Hyperthyroidism results in a “speeding up” of many of the body’s functions showing some of the following symptoms:
- Increased appetite
- Sweating or feeling warm
- Weight loss
- Feeling of a racing heart or the heart thumping (also known as ‘palpitations’)
- Intolerance to heat
- Irregular periods
- Irritability or nervousness
Causes of hyperthyroidism
An autoimmune disease
The major cause of hyperthyroidism is an autoimmune disease, such as Graves’ disease. This is caused by the abnormal presence of antibodies that stimulate the production of TSH and therefore of T3/T4.
Hyperthyroidism may also result from secretion of excess hormone by the thyroid gland itself e.g. from abnormal nodules or from a goitre (swelling of the gland).
Rarely, Hashimoto’s disease causes an initial phase of elevated thyroid function prior to the low functioning phase.
This is a, usually, transient abnormality in thyroid function following pregnancy. It can result in increased or reduced thyroid function and sometimes even one after another.
De Quervain’s thyroiditis
Another, rarer, cause of hyperthyroidism is De Quervain’s thyroiditis. This is caused by inflammation of the thyroid gland, usually as a result of viral infection. Symptoms such as those associated with a viral illness, such as fever, may occur or the gland may be tender to touch.
Note that the medication most commonly associated with abnormalities in thyroid function is amiodarone. This is a drug used in the treatment of heart abnormalities.
Blood results in hyperthyroidism
The hypothalamus, pituitary and thyroid all send chemical signals to one another. The relationship between the pituitary and thyroid is known as a ‘negative feedback cycle’.
This means that when T3 and T4 levels are high, this signals to the pituitary that enough of these hormones are present and that the pituitary should stop producing TSH.
Therefore, when thyroid hormone levels are incorrectly elevated, as we would see in hyperthyroidism, we can expect TSH levels to be low.
TSH – Thyroid Stimulating Hormone
T3 – Triidothyronine
T4 – Thyroxine