What is the pathophysiology of hypopituitarism (panhypopituitarism)?

Updated: Jun 09, 2020
  • Author: Bernard Corenblum, MD, FRCPC; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

When pituitary hormone production is impaired, target gland hormone production is reduced because of a lack of trophic stimulus. Normally, subphysiologic target hormone levels stimulate the pituitary gland to increase trophic hormone production; however, in hypopituitarism, the pituitary gland response is absent, suboptimal, or inappropriate (with biologically inert hormone production). This results in progressive secondary failure of the target glands. Patients with hypopituitarism typically present with low target hormone levels accompanied by low or inappropriately normal levels of the corresponding trophic hormone.

The tropic hormone level may appear to be within the reference range with a corresponding subphysiologic target hormone level. Such a tropic hormone level would be inappropriately low for the subphysiologic target hormone level. Sometimes, the assayed tropic hormone level may be biologically inert.

Thus, pituitary function is assessed by the target gland function, not by measuring the pituitary hormone as an isolated event. This is in contrast to target gland function being assessed by the pituitary hormone. For example, adequate pituitary thyrotropin secretion is best assessed by the serum free thyroxin. Primary thyroid gland hypofunction is best assessed by the serum thyrotropin. A low serum free thyroxin yet normal serum thyrotropin indicates pituitary, not thyroid, disease, and central hypothyroidism would be missed by only measuring serum thyrotropin.


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