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Hyponatremia (Low Sodium) (cont.)

Hyponatremia Causes

Hyponatremia occurs because of an imbalance of water and sodium. Most frequently it occurs when excessive water dilutes the amount of sodium in the body or when not enough total sodium is present in the body. A common classification of hyponatremia is based on the amount of total body water that is present.

Normal volume (euvolemic) hyponatremia

The amount of water in the body is normal, but an anti-diuretic hormone is being inappropriately secreted (SIADH =syndrome of inappropriate ADH secretion) from the pituitary gland. This may be seen in patients with pneumonia, small cell lung cancer, bleeding in the brain, or brain tumors

Excess volume (hypervolemic) hyponatremia

Too much total body water dilutes the amount of sodium contained in the body. This can be seen in heart failure, kidney failure, and liver diseases like cirrhosis. This situation is somewhat misnamed because while there is increased total body water, there may be a relative decrease of fluid within the bloodstream. Because of the underlying disease, fluid leaks into the space between tissues (called the third space) causing swelling of the extremities or ascites, fluid within the abdominal cavity.

Inadequate volume (hypovolemic) hyponatremia

The amount of water in the body is too low as can occur in dehydration. The anti-diuretic hormone is stimulated, causing the kidneys to make very concentrated urine and hold onto water. This may be seen with excessive sweating and exercising in a hot environment. It can also occur in patients with excess fluid loss due to vomiting and diarrhea, pancreatitis, and burns.

Specific situations

  • Hyponatremia may be a side effect of medications, especially diuretics or water pills used to help control blood pressure. This class of drugs can cause excessive loss of sodium in the urine.
  • Hormonal diseases such as Addison's disease or adrenal insufficiency and hypothyroidism may be associated with low sodium levels.
  • Polydipsia, or excessive water intake, may cause "water intoxication," diluting sodium levels. This is occasionally associated withpsychiatric illness.
  • In some people who exercise, their concern about the potential for dehydration causes them to drink more water than they lose by perspiration. This may cause significant hyponatremia and has been known to be fatal in marathon participants who drink too much fluid without replacing lost sodium, in excess of what their thirst mechanism dictates.
  • In infants, hyponatremia may occur if the baby is fed tap water instead of formula or a balanced electrolyte solution like Pedialyte.
  • Drug overdose with MDMA (ecstasy) is associated with hyponatremia.
Medically Reviewed by a Doctor on 8/13/2015

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