Small cell carcinoma
Small cell carcinoma

Dilutional hyponatremia (SIADH)

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

Alternative Names:
Syndrome of inappropriate antidiuretic hormone secretion; SIADH

Causes, incidence, and risk factors:

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:
Signs and tests:
Treatment:
The goal 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):
The outcome is related to the underlying disease.
Complications:
Calling your health care provider:
Call your health care provider if symptoms of dilutional hyponatremia occur.
Prevention:
Prompt treatment of causative conditions may be helpful.

Review Date: 2/14/2002
Reviewed By: Stephanie Fish, M.D., Division of Endocrinology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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