Syndrome of Inappropriate Antidiuretic Hormone Secretion

Syndrome of inappropriate antidiuretic hormone (SIADH) secretion, a potentially life-threatening condition, is marked by excessive release of antidiuretic hormone (ADH), which disturbs fluid and electrolyte balance. SIADH occurs secondary to diseases that affect the osmoreceptors (supraoptic nucleus) of the hypothalamus. The prognosis depends on the underlying disorder and the patient's response to treatment.

Causes of SIADH

Usually, SIADH results from oat cell carcinoma of the lung, which secretes excessive ADH or vasopressor-like substances. Other neoplastic diseases (such as pancreatic and prostatic cancers, Hodgkin's disease, and thymoma) may also trigger SIADH. Additional causes include:

• central nervous system (CNS) disorders, including brain tumor or abscess. cerebrovascular accident, head injury, and Guillain-Barre syndrome
• pulmonary disorders (such as pneumonia, tuberculosis, and lung abscess) and positive-pressure ventilation
• drugs (for example. chlorpropamide, tolbutamide. vincristine, cyclophosphamide, haloperidol, carbamazepine, clofibrate, morphine, and thiazides)
• miscellaneous conditions (such as myxedema and psychosis).

Signs & Symptoms of SIADH

Common Symptoms & Signs includes:

• Muscle spasms or cramps
• Restlessness
• Loss of appetite
• Weight gain
• Headache
• Irritability
• Fatigue
• Abnormal mental status
  • Consciousness, decreased
  • Confusion
  • Possible coma

Diagnostic Tests

In addition to a complete medical history and physical examination, to confirm diagnosis of SIADH, blood tests will need to be performed to measure sodium, potassium chloride levels, and osmolality (concentration of solution in the blood).

Treatment

Treatment for a patient with SIADH is based primarily, on the patient's symptoms and begins with restricted water intake (500 to 1,000 ml/day). Some patients who continue to have symptoms are given a high-salt, high-protein diet or urea supplements to enhance water excretion. Or they may receive demeclocycline or lithium to help block the renal response to ADH.

Rarely, with severe water intoxication, administration of 200 to 300 ml of 3% to 5% sodium chloride solution may be needed to raise the serum sodium level. A loop diuretic may also be prescribed to reduce the risk of heart failure after the excess fluid load and the administration of the hypertonic sodium chloride solution. When possible, treatment should include correction of the underlying cause of SIADH. If SIADH is due to cancer, success in alleviating water retention may be obtained by surgery, irradiation, or chemotherapy.

Prevention Tips

Prompt treatment of causative conditions may be helpful.