Hypopituitarism is the deficient production of one or more pituitary hormones. The pituitary sits below the hypothalamus at the base of the brain and has two parts: the anterior lobe makes growth hormone (GH), the gonadotropins (luteinizing hormone and follicle-stimulating hormone), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH) and prolactin, while the posterior lobe stores and releases antidiuretic hormone (ADH). Because the anterior lobe works under hypothalamic control, deficiency can arise in the gland itself or in the hypothalamus and its stalk above it. Each hormone belongs to an axis, the chain from hypothalamus to pituitary to target gland, and hypopituitarism can affect a single axis or several at once, up to panhypopituitarism, in which all the pituitary hormones are deficient.
Choose a route through this family
The topic is learned in three steps: why hormones are lost, how the loss shows itself, and how it is confirmed and treated. A reader new to the topic can begin with how common the condition is and which causes dominate at different ages, then work through why each hormone is lost.
- Epidemiology of hypopituitarism: how often hypopituitarism occurs, which causes are most common at different ages, and how it affects survival.
- Causes of hypopituitarism: the inherited, neoplastic, vascular, inflammatory, infectious and post-irradiation causes, organised by category.
- Developmental causes of hypopituitarism: the congenital and perinatal conditions, from pituitary damage around birth to the transcription-factor mutations that impair how the gland forms.
- Hypothalamic endocrine dysfunction: the hypothalamic disorders that chiefly disturb GnRH, including Kallmann syndrome, Bardet-Biedl syndrome and leptin-related hypogonadism.
- Acquired hypopituitarism: the tumours, trauma, vascular events, inflammatory and infiltrative disease, checkpoint inhibitors, infections and cranial irradiation that damage a previously normal gland.
Once the causes are clear, the next question is how the loss shows itself, first as a whole and then axis by axis.
- Clinical manifestations of hypopituitarism: what each deficient hormone does, and how the presentation differs between acute and chronic deficiency.
- Growth hormone deficiency: why growth failure appears in childhood and how body composition and cardiovascular risk change in adults.
- ACTH and gonadotropin deficiency: how loss of the ACTH axis produces secondary hypocortisolism with a preserved mineralocorticoid axis, and why hypogonadism is often the first sign in adults.
Finally, the tests that confirm the deficiency and the replacement that treats it.
- Diagnosis of hypopituitarism: the basal and dynamic tests, the cortisol thresholds that guide the search for ACTH deficiency, and the pitfalls of IGF-1, TSH and free T4 in central disease.
- Treatment of hypopituitarism: how each deficient axis is replaced, why hydrocortisone precedes levothyroxine, and the emergency management of adrenal crisis and pituitary apoplexy.