Hypothyroidism 

What is it?

Hypothyroidism occurs when the thyroid is underactive and is not producing enough thyroid hormones for the body's need. This will be diagnosed by thyroid function tests

Signs and symptoms

There are many symptoms and signs (or clinical markers) of hypothyroidism, which are dependent on the degree of abnormality of thyroid hormone levels. As the thyroid controls the rate of metabolism, the effects on the body are wide ranging and result in a "slowing" of body function. An individual with hypothyroidism may have some (but rarely all) the following symptoms and signs:

• General: Constant fatigue
• Dermatological: Thinning hair, decreased sweating, paleness, dry skin,
• Neuromuscular: Reduced muscle strength,
• Psychiatric: Depression, reduced memory recall, reduced attention span, irritability
• Metabolic: Insensitivity to the cold and inability to 'get warm', unexplained weight gain and inability to loss weight, decreased appeptite, cold extremities
• Cardiovascular: Bradycardia (decreased heart rate)
• Gastrointestinal: Constipation, reduced bowel movements
• Endocrine: Irregular menstrual cycle (lighter flow, increased time to next period), amenorrhea (absence of menstrual cycle)
• An individual may also present with a goitre (swelling of the thyroid, visible on the neck)

What are the causes?

-Autoimmune thyroiditis – this is when the immune system attacks the thyroid, causing an inflammatory response, resulting in the thyroid not producing enough thyroid hormone. The reason for the immune system to attack the thyroid is unknown.

If autoimmune thyroiditis presents with goitre it is classed as Hashimoto's thyroiditis.

Often with other autoimmune diseases occur with patients with autoimmune thyroiditis such as:

·         Pernicious anaemia - a decrease in red blood cells due to a reduced ability to absorb vitamin B12.

·         Vitiligo - a skin pigmentation disorder, marked by irregular white patches of skin.

·         Addison disease - a rare disease, in which the adrenal glands produce not enough steroid hormones.

·         Coeliac disease - a damaging of the lining of the small intestine resulting in the inability to absorb gluten.

·         Rheumatoid arthritis - an inflammatory disease mainly targeting joints but not limited to joint, with the possibility of affecting surrounding tissues and possibly organs.

Incidence of developing the above and other autoimmune diseases is increased with autoimmune thyroiditis.

-Surgery –removal of all or part of the thyroid can result in hypothyroidism

-Radioiodine – used to treat hyperthyroidism.

-Iodine deficiency – uncommon in the western world, although recent studies have found the teenage girls in the UK to be iodine deficient. Oily fish and milk are high in iodine and are recommended to include in diet, especially those of childbearing age. If you already have hypothyroidism increasing iodine consumption will not alter this.

-Postpartum hypothyroidism – after giving birth, women can develop hypothyroidism for unknown reasons. It can be temporary or permanent

-Lithium induced hypothyroidism – a side effect of taking lithium. Hypothyroidism can also occur with other medications such as Amidarone

-Congenital hypothyroidism – a certain number of children are born with an underactive thyroid, with symptoms present from birth. It is also possible for children to be born without thyroids, although this is rare.

-Pituitary gland defects – may cause hyperthyroidism, as the pituitary gland secretes TSH, which stimulate thyroid hormone production. If too little TSH is produced, the thyroid will not produce enough T4 and T3. This is a very rare cause of hypothyroidism, and pituitary gland problems are rare.

Treatment

The treatment in the UK is Levothyroxine. Levothyroxine functions as a synthetic replacement of thyroxine, which is normally produced by the thyroid gland. It is recommended to take Levothyroixine in the morning prior to breakfast, as iron and calcium rich foods may reduce the effectiveness of drug absorption.

Levothyroxine's active ingredient is levothyroxine sodium. It is not classed as a drug, as it functions to replace a hormone.

Doses depend on the level of thyroid hormone levels, and will be prescribed based on thyroid function tests and symptoms and signs of hypothyroidism.

Side effects are rare and generally will occur with too high a dose, resulting in temporary hyperthyroidism. For a list of hyperthyroidism symptoms click here.

It is advised that if those suffering from angina to consult closely with their doctor before taking Levothyroxine.

Medications, especially related to the endocrine system have been shown to increase the required Levothyroxine dose. It is suggested that medication plan are discussed with a doctor. It is likely that increased monitoring will be required, with regular thyroid function tests if taking another medication which affects the endocrine systme.

If a woman is planning pregnancy or are pregnant, regular thyroid function monitoring is essential for the health of the foetus. This is particularly true throughout the first trimester. Body function changes in pregnancy and especially that of the endocrine system. Read more about pregnancy in hypothyroidism here.

Information about the national thyroid pregnancy project can be found here.

Thyroid function will be checked annually, once thyroid function has returned to normal. People are recommended to consult their GP if they experience any of the symptoms listed.

References

Hueston, W.J. Treatment of Hypothyroidism. American Family Physician. 2001 Nov 15;64(10):1717-1725.