Differential Diagnosis for Hyponatremia

Single Most Likely Diagnosis

• Hypovolemic Hyponatremia: This is often the most common cause of hyponatremia, resulting from a decrease in extracellular fluid volume, which can be due to various reasons such as dehydration, blood loss, or excessive diuretic use. The body's response to hypovolemia leads to the release of antidiuretic hormone (ADH), causing water retention and dilutional hyponatremia.

Other Likely Diagnoses

• Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): A condition where there is an excessive and inappropriate secretion of ADH, leading to water retention and hyponatremia. This can be caused by various conditions, including pulmonary diseases, neurological disorders, and certain medications.
• Heart Failure: Congestive heart failure can lead to hyponatremia due to the activation of the renin-angiotensin-aldosterone system and the release of ADH, resulting in water and sodium retention.
• Nephrotic Syndrome: Severe proteinuria can lead to hypoalbuminemia, which causes a decrease in oncotic pressure, resulting in water movement into the interstitial space and subsequent dilutional hyponatremia.
• Liver Cirrhosis: Cirrhosis can lead to hyponatremia due to the activation of the renin-angiotensin-aldosterone system, increased ADH secretion, and the resulting water and sodium retention.

Do Not Miss Diagnoses

• Adrenal Insufficiency: A life-threatening condition that can cause hyponatremia due to the lack of aldosterone, leading to impaired sodium retention and potassium excretion.
• Myxedema Coma: A severe form of hypothyroidism that can cause hyponatremia due to decreased cardiac output, decreased free water clearance, and increased ADH secretion.
• Cerebral Salt Wasting: A rare condition characterized by the excessive excretion of sodium in the urine, leading to hyponatremia and dehydration, often seen in patients with cerebral disorders.

Rare Diagnoses

• Reset Osmostat: A rare condition where the osmoregulatory mechanism is reset, leading to a new threshold for ADH secretion and thirst, resulting in hyponatremia.
• Pseudohyponatremia: A condition where laboratory measurements falsely indicate hyponatremia, often due to high levels of lipids or proteins in the blood.
• Hyponatremia due to Beer Potomania: A rare cause of hyponatremia seen in individuals who consume large amounts of beer, which is very low in sodium, leading to a dilutional effect.