Hypothyroidism

Published on 01/03/2015 by admin

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Last modified 01/03/2015

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Hypothyroidism

Hypothyroidism usually develops slowly. It is therefore easily missed clinically and clinical biochemistry has an important role to play in diagnosis.

Clinical features

The clinical features of hypothyroidism include:

lethargy and tiredness

cold intolerance

dryness and coarsening of skin and hair

slow relaxation of muscles and tendon reflexes

many other associated signs including anaemia, dementia, constipation, bradycardia, muscle stiffness, carpal tunnel syndrome, subfertility and galactorrhoea.

Causes

Over 90% of cases of hypothyroidism occur as a consequence of:

autoimmune destruction of the thyroid gland (Hashimoto’s disease)

radioiodine or surgical treatment of hyperthyroidism.

Rarer causes include:

transient hypothyroidism due to treatment with drugs such as lithium carbonate

TSH deficiency, which may be a component of panhypopituitarism

congenital defects such as blocks in the biosynthesis of T₄ and T₃, or end-organ resistance to their action

severe iodine deficiency.

Diagnosis

Hypothyroidism is caused by a deficiency of thyroid hormones. Primary hypothyroidism is failure of the thyroid gland itself and is one of the most commonly encountered endocrine problems. The demonstration of an elevated TSH concentration is usually diagnostic. Secondary hypothyroidism, failure of the pituitary to secrete TSH, is much less common. Isolated pituitary deficiency of TSH is rare, but impairment of the hypothalamic–pituitary–thyroid axis may happen as a result of any pituitary disease or damage.

Clinical features other than those of hypothyroidism may indicate the need for investigation of pituitary function (see pp. 84–85), and the TRH test will be included in such a protocol.

A strategy for the biochemical investigation of clinically suspected hypothyroidism is shown in Figure 45.1.

Fig 45.1 Strategy for the biochemical investigation of suspected hypothyroidism.

Treatment

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