Primary hypothyroidism

Primary hypothyroidism usually presents with nonspecific symptoms of fatigue, depression, constipation, 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 confirms the diagnosis.

Treatment is with levothyroxine; starting dose depends on age and presence of co-existing cardiac 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). Most cases are due to primary hypothyroidism, a failure of the thyroid gland to produce thyroid hormones. Primary hypothyroidism is defined as thyroid-stimulating hormone (TSH) concentrations above the reference range and free thyroxine concentrations below the reference range.[1]Chaker L, Bianco AC, Jonklaas J, et al. Hypothyroidism. Lancet. 2017 Sep 23;390(10101):1550-62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6619426 http://www.ncbi.nlm.nih.gov/pubmed/28336049?tool=bestpractice.com Secondary hypothyroidism is due to underproduction of TSH by the pituitary gland.[1]Chaker L, Bianco AC, Jonklaas J, et al. Hypothyroidism. Lancet. 2017 Sep 23;390(10101):1550-62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6619426 http://www.ncbi.nlm.nih.gov/pubmed/28336049?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.[2]Cooper DS, Biondi B, Cappola AR. Subclinical hypothyroidism: a review. JAMA. 2019 Jul 9;322(2):153-60. http://www.ncbi.nlm.nih.gov/pubmed/31287527?tool=bestpractice.com Myxedema coma is a rare severe form of hypothyroidism with multiorgan failure.[1]Chaker L, Bianco AC, Jonklaas J, et al. Hypothyroidism. Lancet. 2017 Sep 23;390(10101):1550-62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6619426 http://www.ncbi.nlm.nih.gov/pubmed/28336049?tool=bestpractice.com