Hypopituitarism
Hypopituitarism: Excerpt from Professional Guide to Diseases (Eighth Edition)
Hypopituitarism, which includes panhypopituitarism or dwarfism, 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 the anterior pituitary’s vital hormones — corticotropin, thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), human growth hormone (hGH), and prolactin — plus the posterior pituitary hormone, antidiuretic hormone. 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 in adults is a tumor. Other causes include congenital defects (hypoplasia or aplasia of the pituitary gland); pituitary infarction (most often from postpartum hemorrhage); or 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 females and impotence in men. Growth hormone (GH) deficiency follows; in children, this causes short stature, delayed growth, and delayed puberty. In adults, it causes osteoporosis, decreased lean-to-fat body mass index, adverse lipid changes, and subtle emotional dysphoria and lethargy. Subsequent failure of thyrotropin (decreased TSH levels) causes hypothyroidism; finally, adrenocorticotropic failure (decreased corticotropin levels) results in adrenal insufficiency. However, 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, decreased libido), diabetes insipidus, hypothyroidism (fatigue, lethargy, sensitivity to cold, menstrual disturbances), and adrenocortical insufficiency (hypoglycemia, anorexia, nausea, abdominal pain, orthostatic hypotension).
Postpartum necrosis of the pituitary (Sheehan’s syndrome) characteristically causes failure of lactation, menstruation, and growth of pubic and axillary hair; and symptoms of thyroid and adrenocortical failure.
In children, hypopituitarism causes retarded growth or delayed puberty. Dwarfism usually isn’t 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 half the normal rate — sometimes extending 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 the 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. However, 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 hemianopia, loss of visual acuity and, possibly, blindness. Acute hypopituitarism resulting from surgery or infection is often 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.
Serum insulin–like growth factor 1 (IGF-1) is decreased. Cranial computed tomography (CT) scan or magnetic resonance imaging (MRI) may reveal a tumor or abnormal mass in the pituitary gland of the hypothalamus. Radioimmunoassay showing decreased plasma levels of some or all pituitary hormones, accompanied by end-organ hypofunction, 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.
CONFIRMING DIAGNOSIS Diagnosis of hypopituitarism requires measurement of GH levels in the blood after administration of regular insulin (inducing hypoglycemia) or levodopa (causing hypotension). These drugs should provoke increased secretion of GH. Persistently low GH levels, despite provocative testing, confirm GH deficiency. CT scan, MRI, 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 administration of FSH and human chorionic gonadotropin to boost fertility. GH replacement is recommended for adults as well as children. Replacement is done by administering daily subcutaneous injections of one of two recombinant deoxyribonucleic acid (DNA) GHs, accompanied by follow-up of serum IGF-1 levels. Lean body mass increases, whereas adipose tissue — particularly in the abdomen — decreases. Risk of cardiovascular disease and osteoporosis also decrease with treatment. Many patients also notice an improved sense of well-being.
Somatrem, which is identical to hGH but is the product of recombinant DNA technology, has replaced GHs derived from human sources. It’s effective for treating dwarfism and stimulates growth increases as great as 4"to 6"(10 to 15 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 containing favorite foods — ideally, high-calorie foods. Monitor for weight loss or gain.
❑ If the patient has trouble sleeping, encourage exercise during the day.
❑ 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 body temperature is low, provide additional clothing and covers, as needed, to keep the patient warm.
❑ Darken the room if the patient has a tumor that’s causing headaches and visual disturbances. Help with any activity that requires good vision such as reading the menu. The patient with bilateral hemianopia has impaired peripheral vision, so be sure to stand where he can see you, and advise the 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 supine during levodopa testing.
❑ Instruct the patient to wear a medical identification bracelet. Teach him and his family members how to administer steroids parenterally in case of an emergency.
❑ Refer the family of a child with dwarfism to the 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: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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