ABSTRACT
Hypothyroidism, at the most basic level, is a state of deficient thyroid hormone action in tissues that are dependent on thyroid hormone for normal function. Numerous medications can impair thyroid function, causing primary hypothyroidism; the most notable of these are amiodarone, lithium, alpha interferon, and tyrosine kinase or multikinase inhibitors. Hypothyroidism is also classified accordingly into three degrees of severity, although thyroid failure clearly exists on a continuous spectrum of severity. Measurement of the serum thyroid stimulating hormone (TSH) level is the most sensitive and accurate test for detecting primary hypothyroidism. Current recommendations for screening for hypothyroidism vary greatly across organizations because of insufficient evidence that identifying and treating asymptomatic mild hypothyroidism is beneficial. Treatment of hypothyroidism involves thyroid hormone replacement in quantities sufficient to relieve symptoms and return serum TSH levels into the normal range. Treatment of patients with overt hypothyroidism results in the rapid resolution of most hypothyroid symptoms in the majority of patients.
