Primary hypothyroidism

Patients usually present with nonspecific symptoms of weakness, lethargy, depression, and mild weight gain.

Commonly, disease is subclinical.

Physical exam may show dry skin, thick tongue, eyelid edema, 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.[1]Franklyn JA. Hypothyroidism. Medicine. 2005;33:27-29. 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.[2]Hueston WJ. Treatment of hypothyroidism. Am Fam Physician. 2001;64:1717-1724. http://www.aafp.org/afp/20011115/1717.html http://www.ncbi.nlm.nih.gov/pubmed/11759078?tool=bestpractice.com Subclinical hypothyroidism is a state of usually asymptomatic, mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH.[3]Cooper DS. Clinical practice. Subclinical hypothyroidism. N Engl J Med. 2001;345:260-265. http://www.ncbi.nlm.nih.gov/pubmed/11474665?tool=bestpractice.com Myxedema coma is a rare severe form of hypothyroidism with multiorgan failure.[1]Franklyn JA. Hypothyroidism. Medicine. 2005;33:27-29.