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Thyroid disorders

Metabolic Diseases


by Clive Evers

General outline

Hypothyroidism is one of the most important metabolic causes of reversible cognitive impairment. The term refers to thyroid underfunction within adults, which results in deficits of the thyroid hormones, thyroxine (T4) and triodothyronine (T3). This underfunction may originate in the thyroid itself (primary type) or in the pituitary or hypothalamus which controls the thyroid gland (secondary type).

The main action of the thyroid hormones involves using up energy. This causes an increase in the metabolic rate of most tissues. It also appears to supplement and enhance the metabolic effects of the catecholamines (dopamine, noradrenaline and adrenaline) which have been associated with some major psychiatric illnesses e.g. Dopamine and Parkinson's disease.

The symptoms of hypothyroidism are therefore mainly due to decreased metabolism with an associated slowing of mental and physical activity.

Synonyms

Myxoedema

Symptoms and course

Hypothyroidism is more common after middle age; one per cent of the elderly population suffers from it.

There are more females than males affected on a ratio of 5:1. A picture of dementia develops as an extension of the mental impairment that is common. Due to its gradual progression it is often indistinguishable from a primary dementia. So when hypothyroidism has been long and severe, dementia can develop. The symptoms characteristically develop insidiously and almost every organ of the body is affected.

However dementia is not the only psychiatric symptom of hypothyroidism. It can also present with delirium, delusional disorder, schizophreniform psychosis or major depression. Difficulties will arise through the physical effects of the disease.

The skin can be dry, cold and thickened. A malar flush (reddening of the cheeks) may be seen against a generally pale face, known as ‘strawberries and cream complexion.

The lips are often thick and tinged purple. Hair is coarse and brittle. Neurological disturbances are often reported with deafness, slurred speech, a gruff husky voice, muscle cramps and muscle weaknesses and carpal tunnel syndrome at the wrists. This picture may be complicated with other commonly associated conditions e.g. Diabetes mellitus or pernicious anaemia.

Caregiver problems

Psychological features include mental lethargy, dulling and slowing of all cognitive functions. The patient is readily fatigued and daily routines will take longer.

Memory is often affected from an early stage and the patient becomes apathetic and sluggish. Some patients may also show low mood and irritability. These features will all present demands on the immediate carer.

Causes and risk factors

The thyroid gland, located in the front of the neck just below the larynx, secretes hormones that control metabolism. These are the T3 and T 4 as above.

The secretion of both hormones is controlled by the pituitary gland and the hypothalamus, which is part of the brain. Thyroid disorders may result not only from defects in the thyroid gland itself but also from abnormalities of the pituitary or hypothalamus.

Hypothyroidism or underactivity of the thyroid gland, may cause a variety of symptoms and may affect many body functions. The body’s normal rate of functioning is low. The symptoms may vary from mild to severe with the most severe form called myxedema, which is a medical emergency.

The most common cause of hypothyroidism is Hashimoto’s thryoiditis, a disease of the thyroid gland where the body’s immune system attacks the gland.

Failure of the pituitary gland to secrete a hormone to stimulate the thyroid gland (secondary hypothyroidism) is a less common cause.

Other causes include congenital defects, surgical removal of the thyroid gland, irradiation of the gland or inflammatory concessions.

Risk factors include age over 50 years, female gender, obesity, thyroid surgery and exposure of the neck to x-ray or radiation treatments.

Frequency

Hypothyroidism is more common after middle age; one per cent of the elderly population suffers from it.

There are more females than males affected on a ratio of 5:1. A picture of dementia develops as an extension of the mental impairment that is common.

Diagnostic procedures

A physical examination shows delayed relaxation of the muscles during tests of reflexes. Pale, yellow skin; loss of the outer edge of the eyebrows; thin and brittle hair; coarse facial features; brittle nails; firm swelling of the arms and legs; and mental slowing may be noted.

The diagnosis is confirmed by laboratory tests of serum T3 and T4. In hypothyroidism these concentrations will be low. However it is also necessary to measure serum TSH (thyroid stimulating hormone) which regulates this hormone production and is released from the pituitary gland.

If underfunction of the thyroid is mainly due to disease of the thyroid gland, TSH will be high while it will be low if it is due to secondary pituitary disease. Electrocardiogram (ECG) and electroencephalogram (EEG) measures may also assist.

Hypothyroidism is often confused with early dementia or depression that is resistant to treatment. Suspicions usually arise through the characteristic facial appearance or physical signs. Many old age services in the UK now do thyroid functions tests routinely in the initial assessment.

Care and treatment

Replacement of the deficient thyroid hormone is the basis of treatment and Levothyroxine is the most commonly used medication. The lowest dose effective in relieving symptoms and normalising the TSH is used.

Life-long therapy is needed. Medication must be continued even when symptoms subside. Thyroid hormone levels need to be monitored yearly after a stable dose of medication is established. Patients can return to normal life with treatment but life long medication is necessary. It should be noted that myxedema coma, a medical emergency, can result in death.


Available services

International Thyroid Federation info@thyroid-fed.org http://www.thyroid-fed.org/


References

  • Allardyce, J. The secondary dementias 2: hypothyroidism. Journal of Dementia Care July/August 1996; pp 28/29.
  • Weatherall, DJ et al Oxford Textbook of Medicine.3rd edition. Oxford Medical Publications. 1995.
  • Lishman, W A Organic psychiatry,2nd edition ,Blackwell Scientific Publications. 1987.

 

 
 

Last Updated: vendredi 09 octobre 2009

 

 
  • Acknowledgements

    This information was gathered in the framework of the European Commission financed project "Rare forms of dementia". Neither the European Commission nor any person acting on its behalf is responsible for any use that might be made of the following information.
  • European Union
 
 

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