Primary hypothyroidism

Patients usually present with non-specific symptoms of weakness, lethargy, depression, 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.

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 Sub-clinical 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 Myxoedema coma is a rare severe form of hypothyroidism with multi-organ failure.[1]Franklyn JA. Hypothyroidism. Medicine. 2005;33:27-9.