Hypothyroidism

Abstract

Hypothyroidism is a common condition of thyroid hormone deficiency, which is readily diagnosed and managed but potentially fatal in severe cases if untreated. The definition of hypothyroidism is based on statistical reference ranges of the relevant biochemical parameters and is increasingly a matter of debate. Clinical manifestations of hypothyroidism range from life threatening to no signs or symptoms. The most common symptoms in adults are fatigue, lethargy, cold intolerance, weight gain, constipation, change in voice, and dry skin, but clinical presentation can differ with age and sex, among other factors. The standard treatment is thyroid hormone replacement therapy with levothyroxine. However, a substantial proportion of patients who reach biochemical treatment targets have persistent complaints. In this Seminar, we discuss the epidemiology, causes, and symptoms of hypothyroidism; summarise evidence on diagnosis, long-term risk, treatment, and management; and highlight future directions for research.

Figure 1:. Diagnosis and treatment of primary hypothyroidism

TSH=thryoid-stimulating hormone.

Figure 2:. Interpretation of thyroid function tests associated with hypothyroidism

TSH=thryoid-stimulating hormone. TRH=thyrotropin-releasing hormone. *TSH can also be suppressed.

Figure 3:. Thyroxine absorption test

Protocol for supervised thyroxine absorption test, followed by weekly supervised thyroxine administration. Adapted from reference 115, by permission of Elsevier. TSH=thryoid-stimulating hormone. *Laboratory test values, especially an increase in free thyroxine, can be interpreted already at this stage. †Adequate free thyroxine rise is estimated to be roughly 50% from baseline at 120 min.