Differential Diagnosis of Hyponatremia

The differential diagnosis of hyponatremia can be complex and varied, depending on the clinical context. Here's a categorized approach to help in the diagnosis:

• Single Most Likely Diagnosis

  • Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): This condition is often seen in patients with lung diseases, neurological disorders, or those on certain medications. It's characterized by excessive secretion of ADH, leading to water retention and hyponatremia without edema.

• Other Likely Diagnoses

  • Heart Failure: Patients with heart failure may develop hyponatremia due to decreased effective circulating volume, leading to increased ADH secretion and water retention.
  • Nephrotic Syndrome: Significant proteinuria can lead to hypoalbuminemia, which decreases the oncotic pressure, causing fluid to shift from the vascular space to the interstitial space, and potentially leading to hyponatremia.
  • Liver Cirrhosis: Cirrhosis can cause a decrease in effective circulating volume due to splanchnic vasodilation, leading to increased ADH secretion and subsequent water retention.
  • Hypothyroidism: Can cause decreased cardiac output and decreased free water excretion, leading to hyponatremia.

• Do Not Miss Diagnoses

  • Adrenal Insufficiency: A life-threatening condition that can cause hyponatremia due to decreased aldosterone production, leading to impaired free water excretion and hyperkalemia.
  • Diabetic Ketoacidosis: Though typically associated with hyperosmolarity, diabetic ketoacidosis can sometimes present with hyponatremia, especially if the patient has been drinking large amounts of water.
  • Pseudohyponatremia: Conditions like hyperlipidemia or hyperproteinemia can falsely lower sodium levels in laboratory measurements without actually affecting the patient's serum osmolality.

• Rare Diagnoses

  • Cerebral Salt Wasting: A condition associated with cerebral disorders, leading to excessive renal sodium excretion and hyponatremia.
  • Reset Osmostat: A rare condition where the osmoregulatory mechanism is reset, leading to hyponatremia without a clear underlying cause.
  • Primary Polydipsia: Though not typically considered rare, in the context of hyponatremia differential diagnosis, it's less common than other causes and refers to excessive water drinking leading to water intoxication and hyponatremia.

Each of these diagnoses has distinct clinical and laboratory features that can help guide the diagnosis and management of hyponatremia.