Hypothyroidism refers to underactivity of the thyroid gland. In this condition, the thyroid gland produces less thyroid hormone than normal. This may cause a “slowing down” of many bodily functions. Hypothyroidism is usually permanent, although it may sometimes be temporary.

Hypothyroidism most often occurs due to the failure of the thyroid gland to produce enough thyroid hormone. The main causes include:

1. Hashimoto’s disease

2. • This is the most common cause of hypothyroidism.
   • It is an autoimmune disorder, or “self-attacking-self” disease.
   • This means that proteins (antibodies) produced by our own white blood cells target the thyroid gland, and gradually destroy its ability to produce thyroid hormone.
   • Over time, the thyroid gland fails, causing hypothyroidism.

3. Radioactive iodine treatment

4. • Hypothyroidism often develops as a desired treatment goal after the use of radioactive iodine treatment for high thyroid hormone production (hyperthyroidism).

5. Thyroid operation

   • Previous thyroid surgery can cause hypothyroidism, especially if most of the thyroid gland has been removed.

6. Medication

7. • Some medication including amiodarone and lithium can cause hypothyroidism.

8. Subacute thyroiditis

9. • This causes a painful inflammation of the thyroid.
   • After a period of overactivity (hyperthyroidism), hypothyroidism may occur.

10. Congenital hypothyroidism

11. • A baby may be born with an insufficient amount of thyroid tissue or a problem that does not allow normal thyroid hormone production.

Rarely, hypothyroidism can also be caused by problems in the pituitary gland, not the thyroid.

Some symptoms and physical signs associated with hypothyroidism include feeling constantly tired, having dry skin, hair loss, constipation, leg cramps and weight gain. In women, menstrual periods may become heavier. However, many of these symptoms are not very specific and may be experienced by otherwise normal individuals.

The best way to diagnose hypothy​roidism is by performing a blood test which measures both your T4 and TSH levels. "In hypothyroidism, your T4 level would be low, while your TSH level would be high," say doctors from the Department of Endocrinology​ at Singapore General Hospital (SGH), a member of the SingHealth​ group.

It is treated with thyroxine replacement.

• This is given as a small pill daily, has very few side effects and almost no allergic reactions.
• Once the dose of thyroxine that you require has been established, it is usually stable for life (except during pregnancy) and blood tests may only need to be repeated once a year.
• The correct dose is determined from blood tests including both T4 and TSH levels.

Thyroid hormone replacement therapy is:

• Completely safe.
• Not the same as post-menopausal hormone replacement therapy.
• Should be taken separately from calcium- or iron-containing foods and medication.

Ref: V10

Check out our other articles on thyroid:

Common health problems associated with the thyroid gland

What is hyperthyroidism? How is it treated?