Causes

Sodium is found mostly in the body fluids outside the cells. It is very important for maintaining blood pressure. Sodium is also needed for nerves and muscles to work properly.

When the amount of sodium in fluids outside cells drops, water moves into the cells to balance the levels. This causes the cells to swell with too much water. Although most cells can handle this swelling, brain cells cannot, because the skull bones confine them. Brain swelling causes most of the symptoms of hyponatremia.

In hyponatremia, the imbalance of water to salt is caused by one of three conditions:

• Euvolemic hyponatremia -- total body water increases, but the body's sodium content stays the same
• Hypervolemic hyponatremia -- both sodium and water content in the body increase, but the water gain is greater
• Hypovolemic hyponatremia -- water and sodium are both lost from the body, but the sodium loss is greater

Hyponatremia is the most common electrolyte disorder in the United States.

Causes of hyponatremia include:

• Burns
• Congestive heart failure
• Diarrhea
• Diuretic medications, which increase urine output
• Kidney diseases
• Liver cirrhosis
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Sweating
• Vomiting

Symptoms

Common symptoms include:

• Abnormal mental status
  • Confusion
  • Decreased consciousness
  • Hallucinations
  • Possible coma
• Convulsions
• Fatigue
• Headache
• Irritability
• Loss of appetite
• Muscle spasms or cramps
• Muscle weakness
• Nausea
• Restlessness
• Vomiting

Exams and Tests

The health care provider will perform a complete physical examination to help determine the cause of your symptoms. Blood and urine tests will be done.

The following laboratory tests can confirm hyponatremia:

• Comprehensive metabolic panel (includes blood sodium)
• Osmolality blood test
• Urine osmolality
• Urine sodium

Treatment

The cause of hyponatremia must be diagnosed and treated. In some cases, cancer may cause the condition, and radiation, chemotherapy, or surgery to remove the tumor may correct the sodium imbalance.

Other treatments depend on the specific type of hyponatremia.

Treatments may include:

• Fluids through a vein (IV)
• Medication to relieve symptoms
• Water restriction

Outlook (Prognosis)

The outcome depends on the condition that is causing the problem. In general, acute hyponatremia, which occurs in less than 48 hours, is more dangerous than hyponatremia that develops slowly over time. When sodium levels fall slowly over a period of days or weeks (chronic hyponatremia), the brain cells have time to adjust and swelling is minimal.

Possible Complications

• Brain herniation
• Death
• Possible coma

When to Contact a Medical Professional

Hyponatremia can be a life-threatening emergency. Call your health care provider if you have symptoms of this condition.

Prevention

Treating the condition that is causing hyponatremia can help. If you play any sports, drink fluids that contain electrolytes (sports drinks). Drinking only water while you take part in high-energy athletic events can lead to acute hyponatremia.

Alternative Names

Dilutional hyponatremia; Euvolemic hyponatremia; Hypervolemic hyponatremia; Hypovolemic hyponatremia

References

Skorecki K, Ausiello D. Disorders of sodium and water homeostasis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 117.

Verbalis JG, Berl T. Disorders of water balance. In: Brenner BM, ed. Brenner and Rector's The Kidney. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 13.

Update Date: 5/29/2012

Reviewed by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.