Hyperthyroidism

Hyperthyroidism

Thyrotoxicosis occurs when tissues are exposed to high levels of the thyroid hormones. Used correctly, the term ‘hyperthyroidism’ refers to the over-activity of the thyroid gland, but thyrotoxicosis can also occur from ingestion of too much T₄ or, rarely, from increased pituitary stimulation of the thyroid.

Clinical features

The clinical features of hyperthyroidism may be dramatic and include:

weight loss despite normal appetite

sweating and heat intolerance

palpitation – sinus tachycardia or atrial fibrillation

agitation and tremor

generalized muscle weakness; proximal myopathy

angina and heart failure

oligomenorrhoea and subfertility

eyelid retraction and lid lag.

Causes

Hyperthyroidism can result from:

Graves’ disease (diffuse toxic goitre)

toxic multinodular goitre

solitary toxic adenoma

exogenously administered iodine and iodine-containing drugs, e.g. amiodarone

excessive T₄ and T₃ ingestion.

Graves’ disease is the most common cause of hyperthyroidism, and is an autoimmune disease in which antibodies to the TSH receptor on the surface of thyroid cells appear to mimic the action of the pituitary hormone. The normal regulatory controls on T₄ synthesis and secretion are lacking. Pituitary secretion of TSH is completely inhibited by the high concentrations of thyroid hormones in the blood.

Although the eyelid retraction commonly seen in the patient with Graves’ disease (Fig 46.3

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Tags: Clinical Biochemistry An Illustrated Colour Text 5e

Jun 18, 2016 | Posted by admin in BIOCHEMISTRY | Comments Off

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