Teaching Points:

• Clinical Manifestations:
  • Nocturia (usually first sign), polydipsia, polyuria
• At baseline, [Na] resides in the high normal range as long as patient is able to replete free water.
  • Patients become hypernatremic when they are in an altered stated and unable to replete their free water needs.
  • Ex: Pts are strapped down, kept NPO during acute stresses
• Sodium level becomes impaired during the following conditions:
  • When thirst is impaired or cannot be expressed
  • CNS lesions who have hypodipsia or adipsia.
  • Impaired adults who cannot independently access free water.
• Nephrogenic DI is the most common side effect of lithium.
• Water Deprivation test should be used to distinguish etiologies of polyuria and polydipsia.
• Lithium enters the principal cells via ENaC. Accumulation leads to interference of aquaporin production.
• Chronic Lithium use can lead to irreversible nephrogenic DI.
• Treatment of Li-induced Nephrogenic DI
  • Discontinuation of Lithium
  • If Lithium is to be used, treat with amiloride
    • Only shown to work with mild to moderate nephrogenic DI.
    • Need to check Lithium level as a result of fluid depletion.
  • Other treatment modalities:
    • NSAIDs
    • HCTz and low sodium diet
  • Can also potentially cause RTA and nephrotic syndrome.