Indications for Thyroid Hormone Treatment other than over Thyroid Failure
	Subclinical hypothyroidism There is a consensus forming that subclinical hypothyroidism (raised serum TSH but normal thyroid hormone concentrations) represents the mildest form of thyroid failure, and as such should usually be treated with thyroxine. Those favouring therapy are most influenced by the knowledge that between 25–50% of such patients feel better when taking thyroxine,31 and by the inexorable progression to overt thyroid failure of approximately 5% each year in those who possess antithyroid peroxidase antibodies; a risk which increases with higher serum TSH concentrations 32 . As hyperlipidaemia is common in overt hypothyroidism it was anticipated that treatment of subclinical hypothyroidism with thyroxine would improve the lipid profile. However, most patients with subclinical hypothyroidism do not have increased serum total cholesterol and triglyceride concentrations and no substantial reduction occurs after restoration of serum TSH to normal. Arecent meta-analysis of the effectiveness of therapy of subclinical hypothyroidism on serum lipids showed a median decrease in serum total cholesterol and LDL-cholesterol of only 5%,33 and smaller studies have suggested that thyroxine has no effect on lipid concentrations unless serum TSH is greater than 10 mU/l. Although associations have been recognised between autoimmune thyroid disease 34 and subclinical hypothyroidism 35 and myocardial infarction, the link does not seem to be through hyperlipidaemia. A raised serum TSH concentration does not necessarily imply hypothyroidism and, if there is no obvious reason for the elevation such as previous treatment of hyperthyroidism with surgery or iodine-131, or the presence of other organ specific autoimmune diseases (pernicious anaemia, insulin-dependent diabetes mellitus, Addison’s disease, vitiligo) it is sensible to repeat the measurement in 3–6 months. Furthermore, serum TSH concentrations are not normally distributed within the population and there is a significant tail of values between the upper limit of the reference range of 3.5–5.0 mU/l and 8–10 mU/l which is not associated with evidence of thyroid disease, particularly in men.    Figure 1 summarises the current views of the management of subclinical hypothyroidism.36