Hypopituitarism

Hypopituitarism is partial or complete loss of pituitary hormone production. The anterior pituitary normally signals the adrenal glands, thyroid gland, gonads, and liver; its failure therefore produces deficiencies in the target hormones rather than a problem confined to the brain. Posterior pituitary involvement most often appears as deficient antidiuretic hormone (ADH), causing central diabetes insipidus. The clinical picture depends on which hormonal axes fail and how quickly the loss occurs. Slow loss may be mistaken for depression, aging, anemia, or deconditioning because fatigue, weakness, reduced exercise tolerance, and decreased libido develop gradually. Abrupt ACTH loss can produce life-threatening adrenal crisis. ACTH deficiency causes secondary adrenal insufficiency. Low cortisol impairs vascular responsiveness to catecholamines and reduces the body’s ability to maintain glucose during illness or fasting. The result may be hypotension, nausea, vomiting, weakness, abdominal discomfort, hyponatremia, and hypoglycemia. This pattern differs from primary adrenal insufficiency. In secondary disease, aldosterone is usually preserved because it is regulated mainly by the renin-angiotensin-aldosterone system, not ACTH. Hyperkalemia is therefore less prominent or absent. Patients also do not develop the hyperpigmentation caused by markedly...