Hypopituitarism is the decreased (hypo) secretion of one or more of the eight hormones normally produced by the pituitary gland at the base of the brain. If there is decreased secretion of one specific pituitary hormone, the condition is known as selective hypopituitarism. If there is decreased secretion of most or all pituitary hormones
Most cases of hypopituitarism are due to pituitary adenomas compressing the normal tissue in the gland, and rarely other brain tumors outside the gland—craniopharyngioma, meningioma, chordoma, ependymoma, glioma or metastasis from cancer elsewhere in the body.
Infection,
inflammation and
infiltration
The pituitary may also be affected by infections of the brain (brain abscess, meningitis, encephalitis) or of the gland itself, or it may be infiltrated by abnormal cells (neurosarcoidosis, histiocytosis) or excessive iron (hemochromatosis). Empty sella syndrome is unexplained disappearance of pituitary tissue, probably due to outside pressure. Autoimmune or lymphocytic hypophysitis occurs when the immune system directly attacks the pituitary.
Vascular
As a pregnancy comes to term, a pregnant woman’s pituitary gland is vulnerable to low blood pressure, such as may result from hemorrhage; pituitary damage due to bleeding after childbirth is called Sheehan’s syndrome. Pituitary apoplexy is hemorrhage or infarction (loss of blood supply) of the pituitary. Other forms of stroke are increasingly recognized as a cause for hypopituitarism.
Radiation
Radiation-induced hypopituitarism mainly affects growth hormone and gonadal hormones.[14] In contrast, adrenocorticotrophic hormone (ACTH) and thyroid stimulating hormone (TSH) deficiencies are the least common among people with radiation-induced hypopituitarism.[14] Changes in prolactin-secretion is usually mild, and vasopressin deficiency appears to be very rare as a consequence of radiation.
Other physical
External physical causes for hypopituitarism include traumatic brain injury, subarachnoid hemorrhage, neurosurgery and ionizing radiation (e.g. radiation therapy for a previous brain tumor). Bites from Russell’s vipers have also been known to cause hypopituitarism in approx 29% of cases
Congenital
Congenital hypopituitarism (present at birth) may be the result of complications around delivery or may be the result of insufficient development (hypoplasia) of the gland, sometimes in the context of specific genetic abnormalities. Mutations may cause either insufficient development of the gland or decreased function. Forms of combined pituitary hormone deficiency (“CPHD”) include:
Type
OMIM
Gene
CPHD1
613038
POU1F1
CPHD2
262600
PROP1
CPHD3
600577
LHX3
CPHD4
602146
LHX4
CPHD5 (Septo-optic dysplasia)
182230
HESX1
Kallmann syndrome causes deficiency of the gonadotropins only. Bardet-Biedl syndrome and Prader-Willi syndrome have been associated with pituitary hormone deficiencies.
Palmar erythema, hyperpigmented plaques or non-pitting edema of tibia
Neck
Enlarged or nodular thyroid
Treatment of Hypopituitarism
Treatment of hypopituitarism is threefold removing the underlying cause, treating the hormone deficiencies, and addressing any other repercussions that arise from the hormone deficiencies.
Prolactinomas may respond to dopamine agonist treatment–a medication that mimics the action of dopamine on the lactotroph cells, usually bromocriptine or cabergoline. This approach may improve pituitary hormone secretion in more than half the cases, and make supplementary treatment unnecessary.
Other specific underlying causes are treated as normal. For example, hemochromatosis is treated by venesection, the regular removal of a fixed amount of blood. Eventually, this decreases the iron levels in the body and improves the function of the organs in which iron has accumulated.
Hormone replacement
Most pituitary hormones can be replaced indirectly by administering the products of the effector glands: hydrocortisone (cortisol) for adrenal insufficiency, levothyroxine for hypothyroidism, testosterone for male hypogonadism, and estradiol for female hypogonadism (usually with a progestogen to inhibit unwanted effects on the uterus). Growth hormone is available in synthetic form but needs to be administered parenterally (by injection). The antidiuretic hormone can be replaced by desmopressin (DDAVP) tablets or nose spray. Generally, the lowest dose of the replacement medication is used to restore wellbeing and correct the deranged results, as excessive doses would cause side-effects or complications. Those requiring hydrocortisone are usually instructed to increase their dose in physically stressful events such as injury, hospitalization and dental work as these are times when the normal supplementary dose may be inadequate, putting the patient at risk of adrenal crisis.
Long-term follow up by specialists in endocrinology is generally needed for people with known hypopituitarism. Apart from ensuring the right treatment is being used and at the right doses, this also provides an opportunity to deal with new symptoms and to address complications of treatment.
Difficult situations arise in deficiencies of the hypothalamus-pituitary-gonadal axis in people (both men and women) who experience infertility; infertility in hypopituitarism may be treated with subcutaneous infusions of FSH, human chorionic gonadotropin–which mimics the action of LH–and occasionally GnRH.
Complications
Several hormone deficiencies associated with hypopituitarism may lead to secondary diseases. For instance, growth hormone deficiency is associated with obesity, raised cholesterol and metabolic syndrome, and estradiol deficiency may lead to osteoporosis. While effective treatment of the underlying hormone deficiencies may improve these risks, it is often necessary to treat them directly
