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Hyperthyroidism Causes

Hyperthyroidism: Causes


Top Causes

1. Grave's disease

Grave’s disease, caused by an abnormal immune system response, is the major cause of hyperthyroidism in 60% to 90% of cases. Named after an Irish physician, Robert Graves, this condition is due to the production of antibodies (TRAb). This antibody mimics the thyroid stimulating hormone (TSH) produced by the pituitary gland. TSH regulates the thyroid hormone levels. As a result of TRAb secretion, there is an increased secretion of T3 and T4. This autoimmune response is more common in women than in men.

2. Toxic multinodular goiter

The second most common cause of hyperthyroidism in developed countries is toxic multinodular goiter. This is usually non-cancerous and is characterized by one or more lumps in the thyroid gland. The latter gradually swell in size and increase the production of the thyroid hormones. The sequence of causes for hyperthyroidism are:

a. Iodine deficiency might cause a decreased T4 production.

b. As a result of the decreased T4, there is induction of the thyroid cell hyperplasia. This results in multinodular goiter formation.

c. Due to the hyperplasia, there is an increased chance of mutation of the TSH receptor.

d. The mutated TSH receptor on being active becomes toxic and thereby causes hyperthyroidism.

3. Thyroid adenoma

A benign tumor of the thyroid gland, thyroid adenoma is a typical single nodule which differentiates it from multinodular goiter. Very rarely is this type of adenoma cancerous. A typical thyroid adenoma is a solitary, spherical and encapsulated lesion that is distinctly demarcated from the thyroid gland itself. These nodules generally don’t show any symptoms except for the increased thyroid hormone levels. The ones that show no symptoms are called warm or cold adenomas, while the ones that produce excessive thyroid hormones are called hot adenomas. Women are at a higher risk of thyroid adenoma than men, while a person’s chances of developing thyroid adenoma increase with age.

4. Thyroiditis

Apart from the swelling caused by goiter and adenoma, inflammation of the thyroid gland is due to various other reasons as well. Based on the causes they are further classified as:

a. Acute infectious thyroiditis: Characterized by severe pain in the neck, along with fever, chills and other signs of infections. This is mainly caused by bacteria, staph or a strep infection as a result of which there is an inflammation of the thyroid gland.

b. Sub acute thyroiditis: This might be due to a virus, Coxsackievirus or Echovirus. This is also characterized by a sharp neck pain accompanied with low grade fever, pharyngitis, etc.

c. Postpartum thyroiditis: Affecting 5% of new mothers, postpartum thyroiditis is painless and caused due to the modification of the immune system during pregnancy.

dSilent thyroiditis: Also called as subacute lymphocytic thyroidits, silent thyroiditis is a variant of postpartum thyroiditis. Anti-thyroid antibodies are the underlying causes for this type of thyroiditis.

e. Radiation induced thyroiditisA painful type of thyroiditis, this is caused due to the radioactive therapy used to treat hyperthyroidism, neck and brain cancer.

5. Pituitary adenomas

Pituitary adenomas accounts to nearly 15% of the tumors caused in the brain. These adenomas are usually small in size (less than 10 mm) and are termed as microadenomas. A mere 2% of all pituitary adenomas are TSH-secreting tumors. As a result of the tumor, the TSH hormone levels increase, which has an effect on the increased thyroid hormone levels and thus cause hyperthyroidism.

6. Drug induced hyperthyroidism

Certain medications induce hyperthyroidism. A few of them are:

a. InterferonRegulating the immune system, interferon is given to treat cancer, hepatitis and multiple sclerosis. It is responsible for hyperthyroidism. The high thyroid levels can revert to normal once the drug usage is stopped.

b. Anti-epileptic drugs: Eptoin, a drug used to treat seizures causes thyroid dysfunction.

c. Amiodarone: This iodine containing drug is used in the treatment of irregular heart beat. As a result of iodine presence, it over activates the thyroid tissue, resulting in hyperthyroidism.

d. LithiumUsed to treat bipolar disorders, lithium can cause goiter which might cause increased levels of the thyroid hormone.

7. Hereditary hyperthyroidism and genetic mutations

Heriditary hyperthyroidism is a rare autosomal dominant disorder that stimulates the thyrocytes as a consequence of which there is increased thyroid hormones levels in the body. Also, thyroid hormone resistance caused due to the somatic mutation in the TSH receptor produces elevated levels of the hormones. In most of the cases, Grave’s disease is attributed to hyperthyroidism even without considering hereditary reasons such as above. The difference ought to be diagnosed effectively for the right kind of treatment.

8. Excess iodine intake

There have been cases where hyperthyroidism has been caused by an excessive iodine intake. This is seen especially in patients who have been undergoing treatment for euthyroid iodine deficient goiter, where there is a sudden exposure to excessive iodine.

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