PITUITARY ANTERIOR
LOBE DEFICIENCY
IN ADULTS
Anterior pituitary deficiency is decreased secretion of pituitary hormones caused by a disorder of the pituitary or hypothalamus. Compression of a normal pituitary gland by a pituitary adenoma is the most common cause. Other causes of anterior pituitary failure include pituitary cyst, pituitary surgery, pituitary radiation, infiltrative lesion (e.g., lymphocytic hypophysitis, hemochromatosis), infarction (e.g., Sheehan syndrome), apoplexy, genetic disorder (e.g., pit-1 mutation, POU1F1 mutation), primary empty sella syndrome, and metastatic disease to the sella. Hypothalamic diseases that may cause varying degrees of hypopituitarism include mass lesions (e.g., craniopharyngioma, germinoma, metastatic disease), radiation (e.g., for brain or nasopharyngeal malignancies), infiltrative lesions (e.g., sarcoidosis, Langerhans cell histiocytosis), trauma with skull base fracture, and infection (e.g., viral encephalitis, tuberculous meningitis).
The signs and symptoms related to
anterior pituitary insufficiency may occur slowly or suddenly; may be mild or
severe; and may affect the secretion of a single, several, or all pituitary
hormones. Whereas pituitary apoplexy (see Plate 1-18) is an example of a sudden
onset presentation dominated by abrupt loss of corticotropin
(adrenocorticotropic hormone [ACTH]) secretion, the impact of slow-growing
nonfunctioning pituitary adenomas or radiation therapy on pituitary function
develops over years. Panhypopituitarism is the term used to describe
deficiency of all pituitary hormones. Partial hypopituitarism is more common. In
general, the secretion of growth hormone (GH) and gonadotropins is more likely
to be affected than ACTH and thyrotropin (thyroid-stimulating hormone [TSH]).
The clinical picture may be dominated by secondary hypogonadism from
gonadotropin deficiency. With longstanding gonadal steroid deficiency,
individuals develop fine facial wrinkles around the eyes, mouth, and cheeks.
Pallor, out of proportion to the moderate anemia usually present, is observed.
There is loss of axillary and pubic hair. In women, amenorrhea, infertility,
vaginal dryness and atrophy, hot flashes, breast atrophy, osteoporosis, and loss
of libido occur. In men, secondary gonadal failure may cause infertility,
decreased libido, decreased vitality, decreased testicular size, erectile dysfunction, and osteoporosis.
GH deficiency in adults may be
associated with decreased sense of well-being, increased fat mass, decreased
muscle mass, increased risk of cardiovascular disease, and decreased bone
mineral density.
Prolactin deficiency may result in
the inability to lactate postpartum.
Thyroid deficiency produces a
subnormal temperature, cold intolerance, a low metabolic rate, fatigue, dry
skin, periorbital puffiness (myxedema facies), bradycardia,
anemia, delayed relaxation phase of the deep tendon reflexes, and constipation
(see Plates 2-14 and 2-15). Also, the combined decrease of thyroid hormone and
testosterone may result in loss of the lateral third of the eyebrows.
Adrenal insufficiency is responsible
for low blood pressure, asthenia, weight loss, eosinophilia, and crises of
nausea and vomiting, which may be associated with spontaneous hypoglycemia.
Because the adrenal secretion of aldosterone is
preserved, secondary adrenal failure does not cause salt wasting or
hyperkalemia (see Plate 3-24). Also, the hyperpigmentation characteristic of
primary adrenal failure (see Plate 3-22) is absent. However, both primary and
secondary adrenal failure may cause hyponatremia, a result of inappropriate
secretion of antidiuretic hormone (ADH; vasopressin) and a lack of permissive
effect of cortisol for the kidneys to excrete
free water.
