MedlinePlus Medical Encyclopedia: Dilutional hyponatremia (SIADH)

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Dilutional hyponatremia (SIADH)

Contents of this page:
Illustrations Alternative names Definition Causes, incidence, and risk factors Symptoms Signs and tests	Treatment Expectations (prognosis) Complications Calling your health care provider Prevention

Illustrations

Small cell carcinoma

Alternative names Return to top

Syndrome of inappropriate antidiuretic hormone secretion; SIADH

Definition Return to top

Dilutional hyponatremia is a disorder of fluid and electrolyte balance caused by excessive release of antidiuretic hormone (ADH).

Causes, incidence, and risk factors Return to top

Fluid and electrolyte imbalance in this syndrome result from the inability to excrete dilute urine, retention of water within the body, and low sodium levels. The most common cause of SIADH is a type of lung cancer called "oat cell" or small cell, which secretes excessive ADH.

Other causes are pancreatic cancer, prostate cancer, Hodgkin's disease, central nervous system disorders, pulmonary disorders, certain drugs, thymomas, myxedema, and psychosis. SIADH may also develop in some children during the acute phase of meningitis. Risk factors are related to the causes.

Symptoms Return to top

Weight gain
Loss of appetite
Nausea
Vomiting
Headache
Muscle weakness
Muscle spasms or cramps
Restlessness
Fatigue
Irritability
Abnormal mental status
- Possible coma
- Hallucinations
- Consciousness, decreased
- Confusion
Convulsions

Signs and tests Return to top

Low serum sodium
Low serum osmolality
High urine osmolality
Adequate urine sodium excretion
No edema
No evidence of dehydration

Treatment Return to top

The first line of treatment is to restrict fluid intake to one-half or one liter of fluid per day. The cause of the disorder must be treated, especially in the case of malignancy where radiation, chemotherapy, or surgical removal of the tumor may correct the water retention.

Expectations (prognosis) Return to top

The outcome is related to the underlying disease.

Complications Return to top

Possible coma
Convulsions
Electrolyte imbalances

Calling your health care provider Return to top

Call your health care provider if symptoms of dilutional hyponatremia occur.

Prevention Return to top

Prompt treatment of causative conditions may be helpful.

Update Date: 10/28/2003

Updated by: Irfan A. Agha, M.D., Department of Medicine, Renal Division, St. Louis University, St. Louis, MO. Review provided by VeriMed Healthcare Network.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.