Patients usually present with non-specific symptoms of weakness, lethargy, depression, and mild weight gain.
Commonly, disease is sub-clinical.
Physical examination may show dry skin, thick tongue, eyelid oedema, and bradycardia.
Elevated TSH and low free T4.
Treatment is levothyroxine at a starting dose of 1.6 micrograms/kg daily or 25 micrograms daily in older patients or those with CAD.
Over-treatment is uncommon but can lead to iatrogenic hyperthyroidism.
Hypothyroidism is a clinical state resulting from underproduction of the thyroid hormones T4 and T3.  Most cases (95%) are due to primary hypothyroidism, a failure of the thyroid gland to produce thyroid hormones. The remaining 5% of cases are due to secondary hypothyroidism, underproduction of TSH by the pituitary gland.  Sub-clinical hypothyroidism is a state of usually asymptomatic, mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH.  Myxoedema coma is a rare severe form of hypothyroidism with multi-organ failure. 
Adjunct Clinical Professor
Department of Family Medicine
University of North Carolina
WM declares that he has no competing interests.
Professor of Medicine
Chair of Family Medicine
University of Chicago Medical Center
BE declares that he has no competing interests.
Queen Elizabeth Hospital
SR declares that he has no competing interests.
Caerphilly Miners' Hospital
LP declares that he has no competing interests.
University of Copenhagen
BN declares that she has no competing interests.
Professor of Internal Medicine
Endocrinology Division Chief
Texas Tech University Health Sciences Center - School of Medicine
JL declares that he has no competing interests.
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