Pituitary insufficiency is a syndrome characterized by one or more anterior pituitary hormone deficiencies as a result of aplasia or hypoplasia, destruction, infiltration, compression, or displacement of the hypothalamus and/or pituitary gland (Fig. 18-1). Pituitary insufficiency can be congenital or acquired; familial or sporadic; partial or complete; and transient (reversible) or permanent. Posterior pituitary failure, characterized by decreased concentrations of antidiuretic hormone, is referred as central diabetes insipidus.

Most patients with anterior pituitary insufficiency do not have concomitant posterior pituitary failure. In those in whom central diabetes insipidus is also present, hypophysitis, metastatic cancer, or sarcoidosis should be suspected.

According to a population study conducted in northwestern Spain, the annual incidence of hypopituitarism is 42 cases per million, and the prevalence ranges from 290 to 455 cases per million.

Almost any disease that disturbs the normal interaction between the hypothalamus and the pituitary gland can cause hypopituitarism. The most common etiology of pituitary insufficiency is pituitary damage associated with a pituitary adenoma and/or the effect of its treatment (surgery and/or radiation therapy). Among patients with pituitary macroadenomas, about one third have one or more pituitary hormone deficiencies. Other frequent causes are shown in Box 18-1.

The clinical manifestations of hypopituitarism depend on the extent and severity of the specific pituitary hormone deficiency. If the onset is acute, the patient may be critically ill and present with hypotension and shock, obtundation, and even coma. However, if the onset is chronic and the pituitary deficiency is mild, the patient may complain only of fatigue and malaise.

Aside from delayed relaxation of tendon reflexes in hypothyroid patients, there are no specific or pathognomonic findings on physical exam. Physical findings for specific pituitary hormone deficiencies are as follows: