Thyroid disorders affect majority of organ.If not treated it can cause serious health problems.lets find out what are causes of hypothyroidism in this blog.
What is thyroid gland?
- Thyroid is a gland present in our body. It is located in the neck region infront of the windpipe/trachea. Thyroid gland is shaped like a butterfly , with to lobes connected to each other with the help of isthmus.
- This thyroid gland is very important for the body as it produces 2 hormones: T3 and T4.
- Thyroid hormone plays a crucial role in body’s metabolism and also have effect on the heart and the gastrointestinal tract.
- It provides energy to almost all the cells in our body.
- To know more about how the thyroid hormone is formed please visit our blog on introduction to hyperthyroidism.
- To know more about the effect of thyroid hormone on our body please visit our blog on signs and symptoms of hyperthyroidism.
- When a persons thyroid gland is normal the person is said to be euthyroid.
- If the thyroid gland is overactive or produces excess amount of thyroid hormone then person is said to have hyperthyroid. In this the body’s metabolic rate is increased and all the effect that the thyroid hormone has on the body is exaggerated which causes the clinical signs and
- Similarly if the thyroid gland is underactive or produces very less amount of thyroid hormone then person is said to have hypothyroid. Unlike hyperthyroid in hypothyroid as the thyroid hormone is less it will cause the metabolic rate/basal metabolic rate (BMR) to reduce leading to the body getting less energy.
Causes of hypothyroidism:
Causes of Primary hypo thyroidism
Means the defect is within the thyroid gland.
1. An autoimmune disease
- Normally our body contains certain immune cells which helps our body to fight against any kind of infection, or organisms.
- These cells contain certain receptors by which they recognize the foreign cells and destroy them.
- In an autoimmune condition these immune cells recognize the body’s own cells as foreign and starts to attack them.
- This will lead to damage to the body’s various types of cells.
- One of the major cause of hypothyroidism is an auto immune condition called as the hashimoto’s disease.
- Hashimoto’s disease
- Is also known as chronic lymphocytic thyroiditis or autoimmune thyroiditis.
- As it is an autoimmune disease of the thyroid gland, it will attack the body’s own thyroid gland and causes inflammation.
- Due to this chronic inflammation there occurs decrease in the ability of the thyroid gland to produce the T3 and T4 hormones and thereby makes the gland underactive.
- This condition is seen running in families therefore it may be seen in some of the members of the same family.
2. Radiation exposure to the neck
- When neck is exposed to really very high amount of radiation it destroys the thyroid cells.
- Due lots of cells getting destroyed the amount of thyroid hormones produced are less. This will lead to hypothyroidism.
- Procedures that require radiotherapy to neck are:
- In people with head and neck carcinomas
- Hodgkin’s disease
- Radioactive iodine treatment
NOTE: Radioactive iodine treatment is which is done in people with an over active thyroid. That is it is done in hyperthyroidism.
The end result of this treatment is that the radiation causes destruction of the thyroid cells and therefore produces less T4 (thyroid hormone).
This treatment can cause a person with hyperthyroid to become hypothyroid
3. Which Medications are causes of hypothyroidism?
- Some drugs may hamper the production of the thyroid hormone.
- Some of these medicines are:
- Drugs used in heart disorders – amiodarone also known as Cordarone, Pacerone. Amiodarone contains high amount of iodine which will reduce the formation and secretion of the thyroid hormone and may also hamper the peripheral conversion of the T4 to T3.
- Drugs used for psychiatric illness – lithium (mechanism is that lithium reduces the synthesis and release of the thyroid hormone )
- Drugs used in cancer – interferon alpha, interleukin-2 , and tyrosine kinase inhibitors.
- Anti thyroid drugs – drugs which are used in hyperthyroidism, which causes the reduction in the thyroid hormone this drug if taken in high doses may result in hypothyroidism.
4. Thyroid surgery.
- Removal of thyroid gland is referred to as thyroidectomy.
- When the whole of the gland is removed it is called total thyroidectomy.
- When only a part of the thyroid is removed it is called sub-total thyroidectomy or is only one lobe is removed it is called thyroid lobectomy.
- When the whole of the gland is removed there is no hormone produced , making patient hypothyroid.
- Whereas when only a part of the thyroid gland is removed , the remaining thyroid gland tissue may produce sufficient thyroid hormone to meet the body’s demand, or in some cases it may not be enough and may even cause hypothyroidism.
- Several conditions such as thyroid nodules, and thyroid cancer , hyperthyroidism , goiters requires surgery.
- Depending on how much of the tissue is involved in the disease that much amount of the thyroid is to be removed.
5. Iodine deficiency
- Iodine is the main compound in the formation of thyroid hormone.
- Iodine is provided in the diet by the Iodized table salt.
- Other food sources that contain iodine include shellfish, saltwater fish, seaweed , dairy products and eggs.
- In some rare cases pregnant women after they deliver the baby there may be a sudden and very severe rise in the thyroid levels in the body followed by a sharp fall in the thyroid levels.
- The reason behind this is not yet clear but it is associated with inflammation of thyroid gland.
- It is called as post partum thyroiditis.
- Patients with post partum thyroiditis might become euthyroid and regain normal thyroid levels.
- 2.Sheehan’s syndrome it is a condition which causes postpartum hypothyroididsm.
- This occurs when the patient has lost a massive amount of blood which causes reduced blood supply to the pituitary gland.
- There occurs necrosis of the pituitary gland and therefore there is lack in the hormones from the pituitary.
- As the pituitary plays a role in thyroid hormone production, now there will occur hypothyroidism.
7. Congenital hypothyroidism
- Some newborns the thyroid gland might not be developed properly or may not be functioning properly.
- Both this condition will cause hypothyroidism at birth called as congenital hypothyroidism.
- Such babies have growth and developmental problems as well as mental
- If these babies are screened and treated early in life prognosis may be better.
8. Thyroiditis as causes of hypothyroidism.
- Thyroiditis means inflammation of the thyroid gland.
- This inflammation may be caused due to some viral or bacterial infection, post partum or due to some autoimmune condition.
- Patient will have complains of fever and sore throat with pain while swallowing, pain in the neck and pain on touching the thyroid gland.
- Inflammation will causes the stored thyroid hormone to get leaked out from the gland into the blood stream .
- So in these patient show 2 phases , initially which may last for up to 3 months and then hypothyroidism which usually lasts for 12 to 18 months and maximum people return back euthyroid state.
Causes of Secondary hypothyroidism
This means that the thyroid gland is normal and the defect is some other organ which interferes with the thyroid’s function.
That is the thyroid gland is not stimulated properly by the hypothalamus or pituitary gland.
1) Pituitary gland damage
- Normally our pituitary gland releases a hormone called as TSH (thyroid stimulating hormone).
- As the name suggests this hormone stimulates the thyroid gland and releases the thyroid hormone.
- Very rarely if any problem in the pituitary gland such as Pituitary tumors or pituitary surgery will lead to nonfunctioning of the pituitary gland.
- This will result in reduced secretion of TSH will cause less thyroid hormone formation and secretion.
- End result is patient gets hypothyroidism.
2) Hypothalamus disorder.
- Hypothalamus is the top most site for regulation of thyroid hormone secretion.
- Normally the hypothalamus secretes TRH (TSH releasing hormone) which signals the pituitary gland to releaseTSH.
- This TSH will stimulate the thyroid to produce thyroid hormone.
- In any condition where in there occurs reduced functioning of hypothalamus it will adversely affect the thyroid hormone formation and ultimately lead to hypothyroidism.