Editor—During the past six months I have become aware of an increasing number of patients with normal results of thyroid function tests who are being treated with a daily dose of up to 100 ìg thyroxine—mainly as a result of publicity being given in the lay media to a hypothesis put forward by Gordon R B Skinner and colleagues.2 These biochemically euthyroid patients invariably have several symptoms that are compatible with a clinical diagnosis of hypothyroidism, but many of them also have agreed diagnostic criteria for the chronic fatigue syndrome, a condition that does involve dysfunction of the hypothalamic-pituitary axis but not hypothyroidism.
You can read the full article here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2127520/pdf/9345188.pdf
Source: Shepherd C. Giving thyroid hormones to clinically hypothyroid but biochemically euthyroid patients. Long-term treatment is being used. BMJ. 1997 Sep 27;315(7111):814. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2127520/pdf/9345188.pdf