Primary hypothyroidism

Primary hypothyroidism usually presents with non-specific symptoms of fatigue, depression, constipation, and mild weight gain.

Commonly, disease is sub-clinical.

Physical examination may show dry skin, thick tongue, eyelid oedema, 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 Sub-clinical 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 Myxoedema coma is a rare severe form of hypothyroidism with multi-organ 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