- Author: Bernard Corenblum, MD, FRCPC; Chief Editor: Romesh Khardori, MD, PhD, FACP more...
Hypopituitarism is a clinical syndrome of deficiency in pituitary hormone production. This may result from disorders involving the pituitary gland, hypothalamus, or surrounding structures. Panhypopituitarism refers to involvement of all pituitary hormones; however, only 1 or more pituitary hormones are often involved, resulting in isolated or partial hypopituitarism. (See Pathophysiology and Etiology.)
Pituitary gland physiology
The pituitary gland has 2 parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The anterior pituitary receives signals from the hypothalamus that either stimulate or inhibit secretion of pituitary hormones. These hormones are secreted directly into the systemic circulation, where they act on specific organs.
The actions of the pituitary gland can be modulated at many stages. The pituitary hormones, or target organ hormones, can influence the hypothalamus and the pituitary to decrease or increase pituitary hormone secretion through long and short feedback loops. Hormones secreted by the anterior pituitary include the following:
Thyrotropin, or thyroid-stimulating hormone (TSH)
Gonadotropins, or follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Somatotropin or growth hormone (GH)
Corticotropin, or adrenocorticotropic hormone (ACTH)
The posterior pituitary does not produce its own hormones. The hypothalamus produces 2 hormones, vasopressin (VP) and oxytocin (OXT), that are secreted from the nerve axons into the capillary beds that supply the posterior pituitary, where they are stored in cells and ultimately released into the circulation.
Vasopressin, also called antidiuretic hormone (ADH), primarily acts on the V2 receptors of the distal tubules of the kidney to reabsorb water, which increases total body water and urine osmolality and decreases urine volume. Vasopressin, at high levels, also acts as a pressor on the V1 receptors of vascular smooth muscle. Oxytocin induces labor in pregnant women, causing contraction of uterine smooth muscle; the hormone also initiates the mechanics of breastfeeding.
An adrenal crisis (acute cortisol insufficiency) is life threatening and should be treated promptly. When hypothyroidism occurs concurrently with cortisol insufficiency, glucocorticoid replacement should precede thyroid hormone replacement. This reduces the likelihood of possible cortisol insufficiency resulting from increased demands due to enhanced metabolism. (See Treatment and Medication.)
Patients with hypopituitarism are maintained on hormone replacement therapies for life, unless the causative disorder is reversed by treatment or by natural history. These medically replaced patients are generally asymptomatic but require increased doses of glucocorticoids following any form of stress, emotional or physical. The most common stressor is infection. Not matching glucocorticoid dose to stress causes acute decompensation. These patients present with nausea and vomiting and may be hypotensive and ill-appearing. A patient's initial presentation of undiagnosed hypopituitarism may be with this life-threatening decompensated state under stress.
Education emphasizes the need for lifelong hormone replacement, increased glucocorticoid replacement during stress, and prompt medical attention as appropriate. Regular monitoring to avoid excessive hormone replacement is important.
All patients with hypopituitarism should carry some identification. This is often in the form of an identification bracelet worn on the wrist or neck. Some vendors include more than 20 lines of information in a tiny pendant. Some may need to have a vial of hydrocortisone (Solu-Cortef) 100 mg and a syringe for emergency purposes at home and while travelling.
When pituitary hormone production is impaired, target gland hormone production is reduced because of a lack of trophic stimulus. Normally, subphysiologic target hormone levels stimulate the pituitary gland to increase trophic hormone production; however, in hypopituitarism, the pituitary gland response is absent, suboptimal, or inappropriate (with biologically inert hormone production). This results in progressive secondary failure of the target glands. Patients with hypopituitarism typically present with low target hormone levels accompanied by low or inappropriately normal levels of the corresponding trophic hormone.
The tropic hormone level may appear to be within the reference range with a corresponding subphysiologic target hormone level. Such a tropic hormone level would be inappropriately low for the subphysiologic target hormone level. Sometimes, the assayed tropic hormone level may be biologically inert.
Thus, pituitary function is assessed by the target gland function, not by measuring the pituitary hormone as an isolated event. This is in contrast to target gland function being assessed by the pituitary hormone. For example, adequate pituitary thyrotropin secretion is best assessed by the serum free thyroxin. Primary thyroid gland hypofunction is best assessed by the serum thyrotropin. A low serum free thyroxin yet normal serum thyrotropin indicates pituitary, not thyroid, disease, and central hypothyroidism would be missed by only measuring serum thyrotropin.
Causes of pituitary insufficiency include pituitary adenomas or other intrasellar and parasellar tumors, inflammatory and infectious destruction, surgical removal, radiation-induced destruction of pituitary tissue, traumatic brain injury (TBI), subarachnoid hemorrhage, and postpartum pituitary necrosis (Sheehan syndrome). Similar diseases originating in the hypothalamus or pituitary stalk may also result in pituitary insufficiency.
Pituitary tumors, or adenomas, are the most common cause of hypopituitarism in adults, although traumatic brain injury as a cause is being more frequently recognized.
Hypopituitarism resulting from pituitary adenomas is due to impaired blood flow to the normal tissue, compression of normal tissue, or interference with the delivery of hypothalamic hormones via the hypothalamus-hypophysial portal system.
In primary pituitary destruction, the anterior pituitary is destroyed, causing a deficiency in some or all pituitary hormones, including prolactin. Disease involving the hypothalamus or pituitary stalk may cause pituitary hormone deficiency with an elevated serum prolactin. Pituitary tumors, or adenomas, can be secretory or nonsecretory. Approximately 30% of all macroadenomas larger than 10 mm produce at least 1 hormone.
Hypothalamic disease involves destruction of the hypothalamus. This causes a deficiency or loss of hypothalamic regulatory hormone input to the pituitary, which leads to the loss of anterior pituitary hormone secretion, with an elevated serum prolactin level. Loss of antidiuretic hormone (ADH) may have concomitant diabetes insipidus.
Hypersecretion of the secretory pituitary tumor hormone is suggestive of an adenoma. Another indication of a pituitary adenoma is a deficiency in some pituitary hormones with concomitant hyperprolactinemia. Normally, dopamine, produced in the hypothalamus, inhibits prolactin secretion by the anterior pituitary. Compressing the pituitary stalk decreases the inhibitory effect of dopamine and increases prolactin levels.
Longstanding target gland disease may result in hyperplasia of the relevant pituitary cell secreting the tropic hormone, the level of which would be elevated, with an enlarged pituitary gland simulating a mass. Although uncommon, this may appear to be a pituitary adenoma, but the target gland is not hyperfunctioning.
Another common intracranial tumor is craniopharyngioma, a squamous cell tumor that arises from remnants of the Rathke pouch. One third of these tumors extend into the sella, while approximately two thirds remain suprasellar.
Sheehan syndrome occurs with a large volume of postpartum hemorrhage. During pregnancy, the pituitary gland enlarges due to hyperplasia and hypertrophy of the lactotroph cells, which produce prolactin. The hypophyseal vessels, which supply the pituitary, constrict in response to decreasing blood volume, and subsequent vasospasm occurs, causing necrosis of the pituitary gland. The degree of necrosis correlates with the severity of the hemorrhage.
As many as 30% of women experiencing postpartum hemorrhage with hemodynamic instability may develop some degree of hypopituitarism. These patients can develop adrenal insufficiency, hypothyroidism, amenorrhea, diabetes insipidus, and an inability to breastfeed (an early symptom). Lymphocytic hypophysitis occurs most commonly in the postpartum state and may appear as Sheehan syndrome with postpartum hypopituitarism.
Pituitary apoplexy denotes the sudden destruction of the pituitary tissue resulting from infarction or hemorrhage into the pituitary. The most likely cause of the apoplexy is brain trauma; however, it can occur in patients with diabetes mellitus, pregnancy, sickle cell anemia, blood dyscrasias or anticoagulation, or increased intracranial pressure. Apoplexy usually spares the posterior pituitary and solely affects the anterior pituitary. In patients with such underlying diseases, Sheehan syndrome can occur with lesser degrees of postpartum hemorrhage or hypotension.
Head trauma from a motor vehicle accident, a fall, or a projectile can cause hypopituitarism by direct damage to the pituitary or by injuring the pituitary stalk or the hypothalamus. Hypopituitarism may occur immediately, or it may develop months or years later. Recovery is uncommon. Many studies show an incidence of 15-40%, but a study by Kokshoorn et al found the incidence of posttraumatic hypopituitarism to be low.
Other causes of hypopituitarism include empty sella syndrome and infiltrative diseases. Empty sella syndrome occurs when the arachnoid herniates into the sella turcica through an incompetent sellar diaphragm and flattens the pituitary against bone, but resulting pituitary insufficiency is uncommon. Infiltrative diseases, such as Wegener granulomatosis and sarcoidosis, can cause destruction of the anterior pituitary. Lymphocytic hypophysitis is an autoimmune destructive disease that may be directed towards the pituitary or its stalk.
Physiologic or psychological states can influence the hypothalamus by impairing synthesis and secretion of regulating hormones. For example, poor nutrition may impair the hypothalamic secretion of gonadotropin-releasing hormone (GnRH), resulting in reversible pituitary gonadotropin deficiency. Medications may affect measured hormone levels, such as opioids decreasing serum LH and testosterone.
The degree of hormone deficiency varies greatly and depends on the extent of the process and its location. Some functional causes include emotional disorders, changes in body weight, habitual exercise, anorexia, bulimia, congestive heart failure (CHF), renal failure, and certain medications.
Hypopituitarism occurs in adult patients after cranial radiotherapy performed to treat nonpituitary tumors. Thus, patients who undergo cranial radiotherapy should be periodically assessed for pituitary functions.
Additional causes of hypopituitarism include the following:
- Histiocytosis X
- Iatrogenic causes - Radiation,[4, 5] surgery, and withholding of chronic glucocorticoid replacement
- Kallmann syndrome
- Lymphocytic hypophysitis
- Transsphenoidal adenomectomy
- Congenital - Usually presents in childhood, but can present later with features such as delayed puberty; heritable pituitary disease usually involves homeodomain transcription factors
With regard to item 9 above, in a study of 435 patients, Fatemi et al found evidence that the likelihood of hypopituitarism development after transsphenoidal adenoma removal is higher when the tumor is larger than 20 mm. In contrast, some with hypopituitarism prior to adenomectomy may have improved pituitary function following surgery, if the cause of the hypopituitarism was increased suprasellar pressure resulting from the mass itself.
Hypopituitarism is listed as a rare disorder by the National Institutes of Health (NIH), affecting less than 200,000 individuals in the United States. Internationally, hypopituitarism has an estimated incidence of 4.2 cases per 100,000 per year and an estimated prevalence of 45.5 cases per 100,000 without gender difference.
Regal et al reported the first study detailing prevalence and incidence of hypopituitarism in a population in northwestern Spain. They studied an adult population of 146,000 and found a prevalence of 45.5 cases per 100,000 population.
The incidence of permanent pituitary deficiency following traumatic brain injury has yet to be determined.
Stable patients who are diagnosed with hypopituitarism have a favorable prognosis with replacement hormone therapy. Patients with acute decompensation are in critical condition and may have a high mortality rate.
Four retrospective studies from the United Kingdom and Sweden showed that mortality is increased by 1.3- to 2.2-fold in patients with hypopituitarism, compared with age- and sex-matched cohorts. Morbidity is variable and may result from hormone deficiency, from the underlying disease, or from inadequate long-term replacement therapy. The systemic effects of pituitary hormone deficiencies vary depending on the extent of pituitary involvement. Given that the pituitary acts on numerous endocrine sites, the consequences of pituitary dysfunction range from subclinical disease to panhypopituitarism. Underlying disorders, such as tumors, intracranial lesions, or systemic disease, may be asymptomatic or may cause morbidity that masks the hormone deficiency. Note the following:
Deficiency of ACTH with adrenal crisis or TSH with myxedema may be life threatening
GH deficiency causes more morbidity in children than in adults
Sudden compromise of ACTH production may result in more profound morbidity than slowly progressive deficiency
Gonadotropin deficiency with hypogonadism may insidiously cause morbidity
Morbidity is more profound in congenital hypopituitarism
Inappropriate replacement therapy with thyroxin, glucocorticoids, or sex steroids may be associated with long-term morbidity
A study by O’Reilly et al indicated that in patients with hypopituitarism resulting from nonfunctioning pituitary adenomas, deficiencies of ACTH and gonadotropin increase mortality rates, as do excessive doses of hydrocortisone and suboptimal replacement of levothyroxine. The study included 519 patients, with a median followup of 7.0 years.
Cardiovascular disease is significantly higher among hypopituitary patients. Female patients with hypopituitarism who are receiving controlled thyroid and steroid hormone substitution, but without GH replacement, have a more than 2-fold increase in cardiovascular mortality compared with the general population. Hypopituitary patients have a lower high-density lipoprotein cholesterol level and a higher low-density/high-density lipoprotein ratio. There is a higher incidence of cerebrovascular morbidity and mortality following pituitary radiotherapy.
Other complications of hypopituitarism include visual deficits and, due to a limited ability of the endocrine system to respond appropriately, susceptibility to infection and other stressors. Decreased quality of life has been documented by standardized questionnaires.
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