| Clinical disorders of thyroid function
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| Thyroid disease is common, affecting almost 3% of the population; nine times as many women as men are affected
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| The symptoms of hypothyroidism are nonspecific and easily missed. A 60-year-old woman comes to the outpatient clinic and complains of weight gain, intolerance of cold, and tiredness. She also says that she has recently become less alert mentally, but attributes this to aging. She says that two members of her family had 'thyroid trouble'. On examination, she is moderately obese, has dry, cool skin and a puffy face. The thyroid gland is not palpable. Her thyroxine (T4) was 15 nmol/L (normal range: 55-144 nmol/L) and TSH was 25 mU/L (range 0.4-4 mU/L) (see Fig. 37.5). |
| Comment. Symptoms of hypothyroidism at an early stage can be fairly non-specific, as they are in this case. The best laboratory test for the diagnosis of hypothyroidism is the plasma TSH level. The elevated level of TSH suggests primary thyroid disorder. Subsequently this lady's blood was shown to be positive for the microsomal and antithyroglobulin antibodies. A diagnosis of lymphocytic thyroiditis (Hashimoto's thyroiditis) was made. She was treated with thyroxine. |
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| Greater than 95% of thyroid disease originates in the thyroid gland and much of this is autoimmune in origin. Thyroid autoantibodies can bind to the TSH receptor. If the autoantibodies bind to but do not stimulate the gland, the thyroid hormone production will fall and the patient will be hypothyroid; these patients have an increased plasma TSH and reduced free T4. If the autoantibodies bind and stimulate, the patient will be hyperthyroid (thyrotoxic) with increased plasma free T4 and suppressed TSH (see Fig. 37.5). Hypothalamic and pituitary causes of hypothyroidism are often the
result of impaired TSH secretion secondary to pressure from an adjacent tumor. Pituitary TSH-secreting tumors are an extremely rare cause of hyperthyroidism.
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