secondary hypothyroidism

Last reviewed 04/2021

Secondary hypothyroidism is seen when there is interference in

  • tyrotropin releasing hormone (TRH) production by the hypothalamus or its delivery via the pituitary stalk
  • thyrotropin production in the pituitary

The most common causes are pituitary adenomas and the surgery and/or radiotherapy used to treat them (1).

The disease is diagnosed by a combination of TSH with free T4:

  • plasma TSH - can be low, within range or mildly elevated
  • free T4 - is low (1)

Patients should be referred to a specialist for further investigations and management. In patients with secondary hypothyroidism, adequacy of thyroxine replacement should be assessed by measuring free T4 levels (1).