Syndrome of inappropriate antidiuretic hormone
Syndrome of inappropriate antidiuretic hormone: Excerpt from Handbook of Diseases
Excessive release of antidiuretic hormone (ADH) disturbs fluid and electrolyte balance in syndrome of inappropriate antidiuretic hormone secretion (SIADH). The excessive ADH causes an inability to excrete dilute urine, retention of free water, expansion of extracellular fluid volume, and hyponatremia.
SIADH occurs secondary to diseases that affect the osmoreceptors (supraoptic nucleus) of the hypothalamus. The prognosis depends on the underlying disorder and response to treatment.
Causes
The most common cause of SIADH is small cell carcinoma of the lung, which secretes excessive levels of ADH or vasopressin-like substances. Other neoplastic diseases — such as pancreatic and prostatic cancer, Hodgkin’s disease, and thymoma — may also trigger SIADH.
Less common causes include:
❑ central nervous system disorders — brain tumor or abscess, cerebrovascular accident, head injury, and Guillain-Barré syndrome
❑ pulmonary disorders — pneumonia, tuberculosis, lung abscess, and positive-pressure ventilation
❑ drugs — chlorpropamide, vincristine, cyclophosphamide, carbamazepine, clofibrate, metoclopramide, and morphine
❑ miscellaneous conditions — psychosis and myxedema.
Signs and symptoms
SIADH may produce weight gain despite anorexia, nausea, and vomiting; muscle weakness; restlessness; and possibly seizures and coma. Edema is rare unless water overload exceeds 4 L because much of the free-water excess is within cellular boundaries.
Diagnosis
A complete medical history revealing positive water balance may suggest SIADH. Serum osmolality less than 280 mOsm/kg of water and low serum sodium confirm it. Urine osmolality is greater than plasma osmolality.
Supportive laboratory values include high urine sodium secretion (more than 20 mEq/L) without diuretics. In addition, diagnostic studies show normal renal function and no evidence of dehydration.
Treatment
Symptomatic treatment begins with restricted water intake (500 to 1,000 ml/day). With severe water intoxication, administration of 200 to 300 ml of 3% saline solution may be necessary to raise the serum sodium level.
When possible, treatment should include correction of the underlying cause of SIADH. If SIADH results from cancer, success in alleviating water retention may be obtained by surgical resection, irradiation, or chemo-therapy.
If fluid restriction is ineffective, demeclocycline may be helpful by blocking the renal response to ADH.
Special considerations
❑ Closely monitor and record intake and output, vital signs, and daily weight. Follow serum sodium levels.
❑ Observe for restlessness, irritability, seizures, heart failure, and unresponsiveness resulting from hyponatremia and water intoxication.
❑ To prevent water intoxication, explain to the patient and his family why he must restrict his intake.
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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