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 thyroid-stimulating hormone and low free thyroxine.

Treatment is levothyroxine at a starting dose of 1.6 micrograms/kg daily or 25 micrograms daily in older patients or those with coronary artery disease.

Over-treatment is uncommon but can lead to iatrogenic hyperthyroidism.

Hypothyroidism is a clinical state resulting from underproduction of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).[1]Franklyn JA. Hypothyroidism. Medicine. 2005;33:27-9. 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 thyroid-stimulating hormone (TSH) by the pituitary gland.[2]Hueston WJ. Treatment of hypothyroidism. Am Fam Physician. 2001 Nov 15;64(10):1717-24. 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 Jul 26;345(4):260-5. 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;33:27-9.