Primary hypothyroidism

Primary hypothyroidism usually presents with nonspecific symptoms of fatigue, depression, constipation, and mild weight gain; physical exam may show dry skin, eyelid edema, and bradycardia.

Elevated thyroid-stimulating hormone and low free thyroxine confirms diagnosis of overt primary hypothyroidism.

Commonly, disease is subclinical with minimal elevation of thyroid-stimulating hormone and normal thyroxine.

Treatment is with levothyroxine; starting dose depends on age and presence of coexisting 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. Overt 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, Razvi S, Bensenor IM, et al. Hypothyroidism. Nat Rev Dis Primers. 2022 May 19;8(1):30. http://www.ncbi.nlm.nih.gov/pubmed/35589725?tool=bestpractice.com ​ Secondary hypothyroidism is due to underproduction of TSH by the pituitary gland.[2]Taylor PN, Medici MM, Hubalewska-Dydejczyk A, et al. Hypothyroidism. Lancet. 2024 Oct 5;404(10460):1347-64. http://www.ncbi.nlm.nih.gov/pubmed/39368843?tool=bestpractice.com ​ Subclinical hypothyroidism is a state of mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH; it is usually asymptomatic.[3]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 that can lead to multiorgan failure.[2]Taylor PN, Medici MM, Hubalewska-Dydejczyk A, et al. Hypothyroidism. Lancet. 2024 Oct 5;404(10460):1347-64. http://www.ncbi.nlm.nih.gov/pubmed/39368843?tool=bestpractice.com ​​