Pituitary Insufficiency and Hormone Deficiency

Pituitary insufficiency, or hypopituitarism, is the deficient secretion of one or more pituitary hormones, resulting in failure of the downstream target glands and of growth, reproduction, and water balance. It may involve a single axis or all of them (panhypopituitarism) and follows pituitary tumours, their treatment, injury, infiltration, or hypothalamic disease.

Definition

Hypopituitarism is the deficiency of one or more anterior or posterior pituitary hormones, producing secondary hypofunction of the target glands; loss of all anterior pituitary hormones is termed panhypopituitarism.

Scope

This topic covers the causes and patterns of pituitary hormone deficiency, the resulting secondary failure of the thyroid, adrenal, gonadal, and growth axes, and the special features that make this a clinically important condition. It is a reference overview and does not provide replacement regimens, dosing, or diagnostic thresholds.

Core questions

• What causes deficiency of pituitary hormones?
• How does loss of trophic hormones produce secondary target-gland failure?
• Why is secondary adrenal insufficiency a particular concern in hypopituitarism?

Key concepts

• Panhypopituitarism
• Secondary adrenal insufficiency
• Secondary hypothyroidism
• Hypogonadotropic hypogonadism
• Growth hormone deficiency
• Pituitary apoplexy

Mechanisms

Deficiency arises when pituitary or hypothalamic tissue is destroyed or compressed, for example by a macroadenoma, surgery, radiotherapy, head injury, autoimmune or infiltrative disease, or pituitary apoplexy and postpartum infarction (Schneider et al., 2007). Loss of a trophic hormone causes secondary failure of its target gland: deficient adrenocorticotropic hormone produces secondary adrenal insufficiency, deficient thyroid-stimulating hormone produces secondary hypothyroidism, deficient gonadotropins produce hypogonadotropic hypogonadism, and deficient growth hormone alters growth and adult metabolism (Molitch et al., 2011). Mass lesions tend to impair the axes in a characteristic order, and posterior pituitary involvement can additionally disturb water balance (Melmed, 2020).

Clinical relevance

Hypopituitarism connects pituitary disease to the function of every target gland, and secondary adrenal insufficiency in particular is clinically significant. This topic describes how deficiency states arise and are classified; it is a reference framework and does not provide hormone-replacement or emergency-management instructions.

Epidemiology

Hypopituitarism most often results from pituitary adenomas and their treatment, with additional cases from traumatic brain injury, radiotherapy, and infiltrative or autoimmune disease; it is encountered across endocrine practice but precise population rates are addressed in the cited review (Schneider et al., 2007).

History

Early descriptions of pituitary failure, including postpartum pituitary infarction, established that loss of pituitary function produces a recognisable multi-gland deficiency syndrome. Modern characterisation of the individual hormone axes and of the diverse causes of pituitary damage produced the contemporary concept of hypopituitarism summarised in current reviews (Schneider et al., 2007).

Key figures

• Harald Jörn Schneider
• Ezio Ghigo
• Shlomo Melmed
• Mark Molitch

Seminal works

• schneider-2007
• melmed-2020-nejm
• molitch-2011

Frequently asked questions

What is panhypopituitarism?

Panhypopituitarism is the deficiency of all the anterior pituitary hormones, so that the thyroid, adrenal, gonadal, and growth axes all fail because the pituitary signals that normally drive them are absent.

Why is adrenal involvement especially important in hypopituitarism?

Because deficient adrenocorticotropic hormone causes secondary adrenal insufficiency, leaving the body unable to mount an adequate cortisol response, which is a clinically significant feature of the condition; this entry describes the concept rather than its management.