Hyperthyroidism also known as overactive thyroid is a medical condition characterized by increased thyroid gland function leading to high thyroid hormones levels in the blood.
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It is more common in women than men between the ages of 20 to 40 years.
There are three main hormones involved in hyperthyroidism: it is Thyroid stimulating hormone (TSH), free T4 and T3 hormones.
Hyperthyroidism occurs when T4 and T3 in the blood are in excess.
Causes of Hyperthyroidism
Before mentioning causes, lets first understand how a normal thyroid function works
How Thyroid gland and its Hormones function?
Thyroid gland is located in the anterior aspect of the neck just below the larynx (Voice box).
It is stimulated by Thyroid Stimulating Hormone (TSH) to produce Thyroxine (also known as T4) which circulate in the blood and spread all over the body.
In the tissues T4 is converted to T3 which is absorbed by cells, causing an increase in their metabolic rate.
All body cells and tissues have thyroid hormones receptors in them. This means that all of them are activated in the case of excess thyroid hormones
TSH comes from the Pituitary gland in the brain. Its production decreases in the case of high T4 and T3.
Three Common causes of Hyperthyroidism
- Grave’s disease: This is an autoimmune disease whereby circulating Autoantibodies (especially IgG) bind on the TSH receptors in the Thyroid gland causing overproduction of Thyroxine (T4). It is 9 times more common in women than men!
- Toxic Adenoma: Occurs when a single adenoma (non-cancerous tumor) in the thyroid gland produces excess T4. It accounts for about 5% of Hyperthyroidism cases.
- Toxic Multinodular Goitre: Here there are multiple adenomas that produce T4 causing Hyperthyroidism. It is common in elderly.
Rare causes of hyperthyroidism are:
- De Quervain’s thyroiditis: inflammation of the thyroid gland due to antibodies attacking it after a viral infection. It is self-limiting.
- Drugs: Amiodarone, Levothyroxine
- Post-Partum: Occurs in women after giving birth
Signs and Symptoms of Hyperthyroidism
In order to understand signs and symptoms of Hyperthyroidism, you first have to understand the role of T4 and T3 in the body.
The main function of T4 and T3 is to increase basal metabolic rate of all cells and Tissues in the body.
This means that if these hormones are in excess, all systems of the body are affected.
The symptoms are:
- Heat intolerance
- Weight loss despite increased appetite
- Irritability and insomnia
- Hyperactive behaviour
- Shortness of breath
- Protruding eyes, sometimes painful
- Tall stature in children
- Loss of libido
- Excessive thirst which may be mistaken with symptom of diabetes
- Body itch
- Tremors and muscle weakness
Some of the signs of Hyperthyroidism are:
- Exophthalmos: Protruding eyes with the sclera visible above the iris, it is seen in Grave’s disease
- Heart Failure signs
- Goitre: abnormal enlargement of the thyroid gland
- Palmer erythema and painful fingers give a clue of the cause of hyperthyroidism, they are seen in grave’s disease
- In rare cases it may present as psychosis
Psychosis and confusion are seen in rare complication of hyperthyroidism called Thyroid storm.
Investigations and Tests
When hyperthyroidism is suspected based on the signs and symptoms mentioned above, additional tests are performed to confirm the type and the cause in order to provide appropriate treatment.
Initial blood tests are the levels of TSH, freeT4 and T3 in the blood.
Check normal lab ranges of these hormones Here.
In Primary Hyperthyroidism: TSH is low, T4 and T3 are high. This means the problem is in the thyroid gland itself.
In Secondary Hyperthyroidism: TSH is high and T4 and T3 are also high. This happens when there is a TSH secreting tumor in the brain.
Thyroid Autoantibodies are also checked and if present, they indicate Grave’s disease.
Full blood count or CBC may reveal normocytic anaemia.
Temperature and ESR are elevated in de Quervain’s thyroiditis.
Imaging and scans
An Isotope scan is done on the thyroid gland to see if there are any nodules growing there.
In toxic adenoma, there is an “hot” area on the scan (the adenoma) indicating increased T3 and T4 production with the rest of the gland relatively cooler.
CT scan, although not done routinely may show hypertrophy of the eye muscles in patients with Exophthalmos. A Brain tumor can also be identified on the CT scan or an MRI.
An ECG may show cardiac arrhythmias such as Supraventricular Tachycardia and Atrial Fibrillations.
Treatment of Hyperthyroidism
Treatment of Hyperthyroidism depends on the cause.
It can be treated with Drugs to lower Thyroid hormones, Radioactive Iodine or surgery.
Drugs used in Hyperthyroidism
Carbimazole is used to lower T4 and T3. Normal dose is 20 to 40mg per day for 4 weeks.
Then after the dose is gradually reduced.
For Tachycardia and Arrhythmia, propranolol is used.
Radioactive Iodine ( 131I ) is used as First choice treatment in US but in UK and many other countries, drug therapy is first used.
It works by accumulating in the thyroid gland and causing local irradiation, which reduces the overactive state of the gland to normal function.
There is a risk of overtreating leading to Hypothyroidism (hypoactive gland).
Radioiodine is contraindicated in pregnancy and breastfeeding women. It has been proven though that it does not increase the risk of cancer.
Surgical treatment of hyperthyroidism involves removal of part of the thyroid gland to reduce its function. An adenoma is also removed surgically if found.
Thyroid hormones are first reduced before surgery is performed.
The procedure is called subtotal Thyroidectomy. Total thyroidectomy may be done in rare cases.
Complications of thyroid surgery are:
- Laryngeal nerve injury
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