Hypopituitarism
Hypopituitarism: Excerpt from Handbook of Diseases
Hypopituitarism, also known as panhypopituitarism, is a complex syndrome marked by metabolic dysfunction, sexual immaturity, and growth retardation (when it occurs in childhood), resulting from a deficiency of the hormones secreted by the anterior pituitary gland. Panhypopituitarism refers to a generalized condition caused by partial or total failure of all six of this gland’s vital hormones — corticotropin, thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), human growth hormone (hGH), and prolactin. Partial hypopituitarism and complete hypopituitarism occur in adults and children; in children, these diseases may cause dwarfism and delayed puberty. The prognosis may be good with adequate replacement therapy and correction of the underlying causes.
Causes
The most common cause of primary hypopituitarism is a tumor. Other causes include congenital defects (hypoplasia or aplasia of the pituitary gland); pituitary infarction (most commonly from postpartum hemorrhage); partial or total hypophysectomy by surgery, irradiation, or chemical agents; and, rarely, granulomatous disease (tuberculosis, for example). Occasionally, hypopituitarism may have no identifiable cause, or it may be related to autoimmune destruction of the gland. Secondary hypopituitarism stems from a deficiency of releasing hormones produced by the hypothalamus — either idiopathic or possibly resulting from infection, trauma, or a tumor.
Primary hypopituitarism usually develops in a predictable pattern of hormonal failures. It generally starts with hypogonadism from gonadotropin failure (decreased FSH and LH levels). In adults, it causes cessation of menses in women and impotence in men. hGH deficiency follows; in children, this causes short stature, delayed growth, and delayed puberty. Subsequent failure of thyrotropin (decreased TSH levels) causes hypothyroidism; finally, adrenocortical failure (decreased corticotropin levels) results in adrenal insufficiency. When hypopituitarism follows surgical ablation or trauma, the pattern of hormonal events may not necessarily follow this sequence.
Sometimes, damage to the hypothalamus or neurohypophysis from one of the above leads to diabetes insipidus.
Signs and symptoms
Clinical features of hypopituitarism develop slowly and vary with the severity of the disorder and the number of deficient hormones. Signs and symptoms of hypopituitarism in adults may include gonadal failure (secondary amenorrhea, impotence, infertility, and decreased libido), diabetes insipidus, hypothyroidism (fatigue, lethargy, sensitivity to cold, and menstrual disturbances), and adrenocortical insufficiency (hypoglycemia, anorexia, nausea, abdominal pain, and orthostatic hypotension).
Postpartum necrosis of the pituitary (Sheehan’s syndrome) characteristically causes failure of lactation, menstruation, and growth of pubic and axillary hair as well as symptoms of thyroid and adrenocortical failure.
In children, hypopituitarism causes retarded growth and delayed puberty. Dwarfism isn’t usually apparent at birth, but early signs begin to appear during the first few months of life; by age 6 months, growth retardation is obvious. Although these children generally enjoy good health, pituitary dwarfism may cause chubbiness due to fat deposits in the lower trunk, delayed secondary tooth eruption and, possibly, hypoglycemia. Growth continues at less than one-half the normal rate — sometimes into the patient’s 20s or 30s — to an average height of 4";(122 cm) with normal proportions.
When hypopituitarism strikes before puberty, it prevents development of secondary sex characteristics (including facial and body hair). In males, it produces undersized testes, penis, and prostate gland; absent or minimal libido; and inability to initiate and maintain an erection. In females, it usually causes immature development of the breasts, sparse or absent pubic and axillary hair, and primary amenorrhea.
Panhypopituitarism may induce a host of mental and physiologic abnormalities, including lethargy, psychosis, orthostatic hypotension, bradycardia, anemia, and anorexia. Clinical manifestations of hormonal deficiencies resulting from pituitary destruction don’t become apparent until 75% of the gland is destroyed. Total loss of all hormones released by the anterior pituitary is fatal unless treated.
Neurologic signs associated with hypopituitarism and produced by pituitary tumors include headache, bilateral temporal hemianopsia, loss of visual acuity and, possibly, blindness. Acute hypopituitarism resulting from surgery or infection is commonly associated with fever, hypotension, vomiting, and hypoglycemia — all characteristic of adrenal insufficiency.
Diagnosis
In suspected hypopituitarism, evaluation must confirm hormonal deficiency due to impairment or destruction of the anterior pituitary gland and rule out disease of the target organs (adrenals, gonads, and thyroid) or the hypothalamus. Low serum levels of thyroxine (T4), for example, indicate diminished thyroid gland function, but further tests are necessary to identify the source of this dysfunction as the thyroid, pituitary, or hypothalamus.
Radioimmunoassay showing decreased plasma levels of some or all pituitary hormones, accompanied by end-organ hypofunction, including low levels of T4, estrogen, and testosterone, suggests pituitary failure and eliminates target gland disease. Failure of thyrotropin-releasing hormone administration to increase TSH or prolactin concentrations rules out hypothalamic dysfunction as the cause of hormonal deficiency.
Provocative tests are helpful in pinpointing the source of low cortisol levels. Oral metyrapone blocks cortisol synthesis, which should stimulate pituitary secretion of corticotropin and the adrenal precursors of cortisol, measured in urine as hydroxycorticosteroids. Insulin-induced hypoglycemia also stimulates corticotropin secretion. Persistently low levels of corticotropin indicate pituitary or hypothalamic failure. These tests require careful medical supervision because they may precipitate an adrenal crisis.
Diagnosis of hypopituitarism requires measurement of hGH levels in the blood after administration of regular insulin (inducing hypoglycemia) or levodopa. These drugs should provoke increased secretion of hGH. Persistently low hGH levels, despite provocative testing, confirm hGH deficiency. Computed tomography scan, magnetic resonance imaging, or cerebral angiography confirms the presence of intrasellar or extrasellar tumors.
Treatment
Replacement of hormones secreted by the target glands is the most effective treatment for hypopituitarism. Hormone replacement therapy includes cortisol, T4, and androgen or cyclic estrogen. Prolactin need not be replaced. The patient of reproductive age may benefit from cyclic administration of FSH and human chorionic gonadotropin to induce ovulation.
Clinical tip In hypopituitarism, the TSH levels become an unreliable marker for thyroid hormone replacement. Therefore, follow free T4 levels in this patient.
Somatrem and others, identical to hGH but the product of recombinant deoxyribonucleic acid technology, have replaced growth hormones derived from human sources. They’re effective for treating dwarfism and stimulating growth increases as great as 6" (15.2 cm) in the first year of treatment. The growth rate tapers off in subsequent years. After pubertal changes have occurred, the effects of somatrem therapy are limited. Occasionally, a child becomes unresponsive to somatrem therapy, even with larger doses, perhaps because antibodies have formed against it. In such refractory patients, small doses of androgen may again stimulate growth, but extreme caution is necessary to prevent premature closure of the epiphyses. Children with hypopituitarism may also need replacement of adrenal and thyroid hormones and, as they approach puberty, sex hormones.
Special considerations
❑ Caring for patients with hypopituitarism requires an understanding of hormonal effects and skilled physical and psychological support.
❑ Monitor the results of all laboratory tests for hormonal deficiencies, and know what they mean. Until hormone replacement therapy is complete, check for signs of thyroid deficiency (increasing lethargy), adrenal deficiency (weakness, orthostatic hypotension, hypoglycemia, fatigue, and weight loss), and gonadotropin deficiency (decreased libido, lethargy, and apathy).
❑ Watch for anorexia in the patient with panhypopituitarism. Help plan a menu that contains his favorite foods — ideally, high-calorie foods. Monitor for weight loss or gain.
❑ Record temperature, blood pressure, and heart rate every 4 to 8 hours. Check eyelids, nail beds, and skin for pallor, which indicates anemia.
❑ Prevent infection by giving meticulous skin care. Because the patient’s skin is probably dry, use oil or lotion instead of soap. If the patient’s body temperature is low, provide additional clothing and covers, as needed, to keep him warm.
❑ Darken the room if the patient has a tumor that’s causing headaches and vision disturbances. Help with any activity that requires good vision such as reading the menu. The patient with bilateral hemianopsia has impaired peripheral vision, so be sure to stand where he can see you and advise his family to do the same.
❑ During insulin testing, monitor closely for signs of hypoglycemia (initially, slow cerebration, tachycardia, diaphoresis, and nervousness, progressing to seizures). Keep dextrose 50% in water available for I.V. administration to correct hypoglycemia rapidly.
❑ To prevent orthostatic hypotension, be sure to keep the patient in a supine position during levodopa testing.
❑ Instruct the patient to wear a medical identification bracelet. Teach him and his family how to administer steroids parenterally in case of an emergency.
❑ Refer the family of a child with dwarfism to appropriate community resources for psychological counseling because the emotional stress caused by this disorder increases as the child becomes more aware of his condition.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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