The hypothalamus-pituitary-thyroid axis is one of several
hormone regulatory systems from the hypothalamus to the pituitary and ultimately to the peripheral target organs. The hypothalamus and the pituitary gland are in close anatomical proximity at the base of the brain and extended through the pituitary stalk to the sella turcica. The pituitary stalk allows passage of stimulatory and inhibitory
hormones and other signal molecules. The target organs are placed in the periphery and function through stimulation/inhibition by the circulating
pituitary hormones. The several hypothalamus-pituitary-target organ axis systems interact in very sophisticated and complicated ways and for many of them the interactive and integrated mechanisms are still not quite clear. The diagnosis of
central hypothyroidism is complicated by itself but challenged further by concomitant affection of other hypothalamus-pituitary-
hormone axes, the dysfunction of which influences the diagnosis of
central hypothyroidism. Treatment of both the
central hypothyroidism and the other hypothalamus-pituitary axes also influence the function of the others by complex mechanisms involving both central and peripheral mechanisms. Clinicians managing patients with neuroendocrine disorders should become aware of the strong integrative influence from each hypothalamus-pituitary-
hormone axis on the physiology and pathophysiology of
central hypothyroidism. As an aid in this direction the present review summarizes and highlights the importance of the hypothalamus-pituitary-thyroid axis, pitfalls in diagnosing
central hypothyroidism, diagnosing/testing
central hypothyroidism in relation to
panhypopituitarism, pointing at interactions of the thyroid function with other
pituitary hormones, as well as local hypothalamic
neurotransmitters and gut-brain
hormones. Furthermore, the treatment effect of each axis on the regulation of the others is described. Finally, these complicating aspects require stringent diagnostic testing, particularly in clinical settings with lower or at least altered à priori likelihood of
hypopituitarism than in former obvious clinical patient presentations.