Hypopituitarism is the deficient production of one or more pituitary hormones, the hormones that the pituitary gland at the base of the brain releases to regulate the thyroid, adrenal glands, gonads and growth. Its exact frequency has not been well established, partly because partial deficiency produces few symptoms and much of the evidence comes from a small number of population studies. The estimates most often quoted are an incidence of about 1 in 23,000 people per year (new cases each year) and a prevalence of about 1 in 2000 of the population (people affected at a given time).
The mix of causes changes with the age of onset. In adults, a pituitary adenoma is the most common cause of hypopituitarism, and further cases follow the treatment of pituitary disease, such as surgery and cranial irradiation. In children, congenital and developmental disorders make up a larger share of cases, while acquired causes such as craniopharyngioma also contribute.
Hypopituitarism is also associated with reduced survival. Cohort studies and a systematic review report excess mortality compared with the general population, with standardised mortality ratios (observed deaths divided by the deaths expected in the general population) broadly around 1.5 to 2, and the excess falls mainly on cardiovascular and cerebrovascular disease. The increase in cardiovascular mortality persists in patients whose thyroid, gonadal and adrenal axes are replaced but who are not given growth hormone, which suggests that unreplaced growth hormone deficiency is an important contributor.
The most immediately dangerous deficiency is that of adrenocorticotropic hormone (ACTH), the pituitary hormone that drives cortisol production by the adrenal glands. Without a cortisol reserve, an intercurrent illness or a procedure can progress to adrenal crisis, which is preventable when the diagnosis is known and replacement is adjusted for stress.
These figures describe how often the condition occurs and what it costs; why the pituitary fails in the first place depends on the cause.