Central Hypothyroidism
Central hypothyroidism is an underactive thyroid caused not by the thyroid gland itself, but by a problem in the pituitary gland or hypothalamus that control it. It is much less common than primary hypothyroidism.
Because the usual TSH signal is unreliable in this condition, diagnosis and monitoring need a different approach.
Last medically reviewed: 15 November 2025
What causes it
The pituitary produces TSH to stimulate the thyroid. If the pituitary or the hypothalamus above it is damaged — by a tumour, surgery, radiotherapy, traumatic brain injury or rare inflammatory conditions — TSH production falls and the thyroid is under-stimulated.
Some cases are congenital, and others are associated with deficiencies of other pituitary hormones such as cortisol or growth hormone.
Why it is easy to miss
In primary hypothyroidism, TSH is high because the pituitary works harder. In central hypothyroidism, TSH is low or inappropriately normal despite low thyroid hormone — so it can be overlooked if only TSH is checked.
Free T4 is the key test, and a low free T4 with a low or normal TSH should prompt assessment of the pituitary.
How it is managed
Treatment is levothyroxine, as in primary hypothyroidism, but monitoring uses free T4 rather than TSH because TSH is not a reliable guide. Other pituitary hormones must be assessed and treated first where deficient — particularly cortisol, since replacing thyroid hormone before cortisol can be unsafe.
Specialist endocrinology input is essential, and imaging of the pituitary is often arranged.
Frequently asked questions
How is central hypothyroidism different from normal hypothyroidism?
In primary hypothyroidism the thyroid gland fails and TSH is high; in central hypothyroidism the pituitary or hypothalamus fails and TSH is low or normal. Treatment is similar but monitoring differs.
Why is TSH not used to monitor treatment?
Because the pituitary cannot raise TSH normally, TSH does not reflect thyroid hormone levels. Free T4 is used to guide the dose instead.
Is it serious?
It requires specialist care, especially because other pituitary hormones may also be deficient. With correct treatment and monitoring, thyroid hormone levels can be well controlled.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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