Central Hypothyroidism

Central hypothyroidism is thyroid hormone deficiency from pituitary (secondary) or hypothalamic (tertiary) disease.

• Prevalence 1 in 80,000 to 120,000; causes: pituitary adenoma, surgery, radiotherapy, traumatic brain injury, apoplexy, infiltrative disease, hypophysitis, congenital (TSHB, PIT1, PROP1, TRHR mutations), immune checkpoint inhibitors.
• Usually accompanied by other pituitary deficiencies.
• TSH may be low, normal, or mildly raised (biologically inactive).

• Hypothyroid symptoms, often milder (no goitre).
• Features of pituitary disease: headache, visual field defects, hypogonadism, adrenal insufficiency.
• Neonatal: prolonged jaundice, hypotonia, hypoglycaemia.

• Low free T4 with inappropriately low or normal TSH.
• Assess other axes: morning cortisol (or ACTH stimulation), IGF 1, LH/FSH/sex steroids, prolactin.
• Pituitary MRI.
• Exclude non thyroidal illness and drug effect (glucocorticoids, dopamine).

• Levothyroxine 1.6 micrograms/kg/day, started after glucocorticoid replacement if adrenal insufficiency is present (start hydrocortisone first: 15 to 25 mg daily in divided doses).
• Monitor with free T4 (not TSH), aiming at mid to upper reference range.
• Treat the cause (adenoma surgery, dopamine agonists).
• Replace other deficient axes.
• Neonates: early treatment, 10 to 15 micrograms/kg/day.