A 56-year-old woman, Miss TM, presented to her GP complaining of gaining weight, feeling cold and being tired all the time. Her hair and skin were very dry. On questioning she had noticed feeling out of breath more frequently, she was constipated and had generalized aches and pains with occasional tingling in her hands and feet. The GP thought she might be hypothyroid and on examination found her to have cool extremities with myxoedematous changes in the skin, her face was pale with periorbital puffiness, she was bradycardic and her tendon reflexes showed delayed relaxation. There was no goitre (Fig. 14a). The clinical diagnosis was confirmed biochemically when her thyroid function tests showed fT4 of <2.0pmol/L and TSH >75 mU/L. She had a high titre of thyroid peroxidase antibodies. She was started on thyroxine replacement therapy and her symptoms resolved over the next few weeks.
In the developed world, the vast majority of cases of primary hypothyroidism are caused by autoimmune disease or following treatment of thyrotoxicosis with radioactive iodine therapy or surgery. Autoimmune disease is either associated with destructive thyroid antibodies (antithyroid peroxidase antibodies) causing thyroid atrophy or, less commonly, with TSH- receptor-blocking antibodies causing the goitre of Hashimoto’s disease. Drug-induced hypothyroidism may be seen, particularly in people taking lithium therapy and, rarely, congenital abnormalities of the thyroid or dyshormonogenesis may be found. Secondary hypothyroidism, characterized by low thyroxine and TSH concentrations and associated with disorders of the hypothalamo-pituitary axis, is rarely seen in general medical practice.
Control of thyroid hormone synthesis and secretion
Hypothalamic and pituitary control
Thyrotrophin – releasing hormone (TRH)
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