Euvolemic-hypotonic-hyponatremia

(ie, ↑ TBW relative to total body Na)

• SIADH

• Endocrinopathies: ↑ ADH activity seen in glucocorticoid deficiency (co-secretion of ADH & CRH) and severe hypothyroidism/myxedema coma (↓ CO/SVR → ADH release & ↓ GFR)

• Psychogenic polydipsia (Uosm <100, ↓ FEUric Acid): usually intake >15 L/d

• Low solute (↓ UNa, ↓ Uosm) “tea & toast”; beer potomania

• Reset osmostat: chronic malnutrition (↓ intracellular osmoles) or pregnancy (hormonal effects) → ADH physiology reset to regulate a lower [Na]serum