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Hypothyroidism

Author: Dr Shendy Engelina, Core Medical Trainee, Northampton General Hospital, UK. Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, July 2016.

Introduction

Abnormal levels of circulating thyroid hormone (thyroxine) and underlying diseases may lead to alterations in the appearance of skin, hair and nails. The thyroid gland can be overactive, resulting in hyperthyroidism, or underactive, resulting in hypothyroidism, discussed here.

What is hypothyroidism?

In contrast to hyperthyroidism, in hypothyroidism, the thyroid gland is underactive, causing a reduction in thyroxine production.

Who gets hypothyroidism?

Hypothyroidism can occur at any age and gender but is most commonly seen in females during menopausal years (age 40–50 years).

What causes hypothyroidism?

There are several causes for hypothyroidism.

Autoimmune thyroiditis

Autoimmune thyroiditis is also known as atrophic thyroiditis or Hashimoto disease when goitre is present.

Subacute thyroiditis

Subacute thyroiditis is also known as De Quervain thyroiditis.

Iodine deficiency

The element iodine is crucial for thyroxine synthesis.

Iatrogenic hypothyroidism

Hypothyroidism may arise from medications.

Congenital hypothyroidism

Congenital hypothyroidism, or cretinism, may result from the absence or incomplete development of the thyroid gland, defects in thyroid hormone metabolism or hypothalamic-pituitary axis dysfunction. It is rare. 

Rare causes of hypothyroidism

Rare causes of hypothyroidism include:

What are the clinical features of hypothyroidism?

Hypothyroidism results in a reduction in the body’s metabolic rate. It is characterised by:

Other common systemic symptoms due to hypothyroidism include weight gain, cold intolerance, low mood and menstrual disturbances (irregular or heavy period).

Clinical features of congenital hypothyroidism include:

What are the complications of hypothyroidism?

Serious complications may occur if hypothyroidism left untreated:

How is hypothyroidism diagnosed?

Hypothyroidism is diagnosed by thyroid function tests (TFTs).

*Sick euthyroid syndrome commonly occurs in patients who suffer from severe non-thyroidal illness such as sepsis, burns and trauma. It is usually transient and treatment may not be required, as thyroid function typically reverts to normal following disease recovery.

Interpretation of thyroid function tests
TSHFree T4 (thyroxine)Free T3 (triiodothyronine)
(Primary) hyperthyroidism Low High High
Secondary hyperthyroidism High High High
Subclinical hyperthyroidism Low Normal Normal
Primary hypothyroidism High Low Low or normal
Secondary hypothyroidism Low or normal Low Low or normal
Subclinical hypothyroidism Borderline high Normal Normal
Sick euthyroid syndrome Low Low Low

Serum autoantibodies are present in 90–95% of autoimmune thyroiditis. They should include:

Full blood count and inflammatory markers, such as C-reactive protein, are routinely included to screen for anaemia (commonly associated with hyperthyroidism) and systemic infection causing thyroiditis. Creatine kinase is tested to check for myopathy, and lipids are evaluated as hypercholesterolaemia and hypertriglyceridaemia are common in hypothyroidism.

Imaging should include:

What is the treatment for hypothyroidism?

Levothyroxine is the first line of treatment to replace the lack of thyroxine in the body.

Although side effects are uncommon, symptoms of hyperthyroidism can occur when to much thyroxine is taken. This including diarrhoea, irritability, sweating and palpitation.

What is the outcome for hypothyroidism?

The majority of patients respond well to levothyroxine and they usually take this medication for life.

Related information

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