Hypothyroidism is defined as a deficiency of thyroid hormones and is a common condition worldwide.
A distinction is made between latent hypothyroidism (also: subclinical hypothyroidism), where the TSH level is elevated but the free thyroid hormones (fT3 and fT4) are still within the normal range, and manifest hypothyroidism with clinically and laboratory-confirmed thyroid underactivity, where the thyroid gland does not produce enough thyroid hormones.
The prevalence of manifest hypothyroidism is reported to be 0.1% to 2%, and that of the latent form is 4% to 10%. This frequency of the condition is increased in women and older people.
The systemic hypometabolism associated with hypothyroidism leads to numerous well-characterized metabolic-related changes and diseases, such as hyperlipidemia, hypertension, and cardiovascular diseases.
Patients with hypothyroidism can generally undergo surgery, but some important prerequisites and precautions must be observed to avoid perioperative complications. Untreated or inadequately treated hypothyroidism can significantly increase the risk of anesthesia.
Latent hypothyroidism does not constitute a contraindication to elective surgery.
In severe hypothyroidism (reduced fT4, clinical symptoms), medication substitution with L-thyroxine should be performed before surgery, possibly with a slow increase in dosage in older patients or those with heart disease. In urgent surgeries or emergencies, surgery is acceptable with untreated hypothyroidism—then under strict monitoring and possibly with parenteral thyroxine administration.
Sources:
Chaker L, Bianco AC, Jonklaas J, Peeters RP (2017) Hypothyroidism. Lancet 390:1550–1562
Biondi B, Cappola AR, Cooper DS (2019) Subclinical hypothyroidism: a review. JAMA 322:153–160
Moon S, Kim MJ, Yu JM, Yoo HJ, Park YJ (2018) Subclinical hypothyroidism and the risk of cardiovascular disease and all-cause mortality: a meta-analysis of prospective cohort studies. Thyroid 28:1101–1110
Tsai TY, Tu YK, Munir KM, Lin SM, Chang RH, Kao SL, Loh CH, Peng CC, Huang HK (2020) Association of hypothyroidism and mortality in the elderly population: a systematic review and meta-analysis. J Clin Endocrinol Metab 105(6):dgz186