Hyponatremia - Causes

Causes

Based on the above classification, some of the many specific causes of hyponatremia can be listed as follows:

Hypervolemic hyponatremia - Both sodium & water content increase: Increase in sodium content leads to hypervolemia and water content to hyponatremia. Total body water and sodium are regulated independently

• cirrhosis
• congestive heart failure
• nephrotic syndrome
• massive edema of any cause

Euvolemic hyponatremia - total body water increases, but the body's sodium content stays the same

• states of severe pain or nausea
• in the setting of trauma or other damage to the brain
• SIADH (and its many causes)
• Hypothyroidism
• Glucocorticoid deficiency

Hypovolemic hyponatremia - The hypovolemia (extracellular volume loss) is consequent on total body sodium loss but, overall, total body water is increased and is the aetiology of the hyponatremia

• any cause of hypovolemia such as prolonged vomiting, decreased oral intake, severe diarrhea
• diuretic use (due to the diuretic causing a volume depleted state and thence ADH release, and not a direct result of diuretic-induced urine sodium loss)
• Addison's disease in which the adrenal glands do not produce sufficient steroid hormones (combined glucocorticoid and mineralocorticoid deficiency)

Miscellaneous causes of hyponatremia that are not included under the above classification scheme include:

• factitious hyponatremia (due to massive increases in blood triglyceride levels, extreme elevation of immunoglobulins as may occur in multiple myeloma, and extreme hyperglycemia)
• hypothyroidism and adrenal insufficiency (both thyroid hormone and cortisol are required to excrete free water)
• beer potomania and other malnourished states where poor dietary protein intake leads to inadequate urine solute formation thereby impeding the kidney's ability to excrete free water
• primary polydipsia (where the amount of urine solute required to excrete huge quantities of ingested water exceeds the body's ability to produce it; this typically occurs when 12 or more litres of water are ingested per day)