Hypopituitarism is a condition in which the pituitary gland fails to produce sufficient levels of one or more of its hormones. The pituitary gland, a small structure at the base of the brain, controls a wide network of other endocrine glands by releasing hormones that regulate growth, reproduction, thyroid function, adrenal function and fluid balance. When pituitary output is impaired, the downstream effects depend on which hormones are deficient.
In the context of acquired brain injury, including hypoxic-ischaemic brain injury after cardiac arrest, hypopituitarism can occur as a complication of damage to the pituitary gland or the hypothalamus (which regulates pituitary function). Deficiency of cortisol (through impaired ACTH secretion) is the most immediately life-threatening consequence, as cortisol is essential for the stress response and blood pressure regulation. Secondary hypothyroidism (through impaired TSH secretion), growth hormone deficiency and hypogonadism (through impaired LH and FSH secretion) are also recognised complications of acquired brain injury. Diabetes insipidus, caused by impaired ADH secretion, can occur acutely and causes the kidneys to produce large volumes of dilute urine, leading to dehydration and sodium imbalance.
Diagnosis involves blood tests measuring pituitary and target-organ hormone levels, along with dynamic stimulation tests where a single hormone level is not conclusive. MRI of the pituitary and hypothalamic region may be requested. Pituitary function testing is not routinely performed after every cardiac arrest, but should be considered if survivors experience unexplained fatigue, weight changes, low blood pressure, sexual dysfunction or mood disturbance that does not respond to standard psychological support.
Treatment involves hormone replacement therapy tailored to the specific deficiencies identified: hydrocortisone for cortisol deficiency, levothyroxine for hypothyroidism, and so on. Patients with hypopituitarism require ongoing endocrinology follow-up and should carry steroid emergency information cards if they are on hydrocortisone replacement, as they need increased doses during illness or surgery.
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