What is the first-line management for asymptomatic or mildly symptomatic hyponatremia due to SIADH?

• A. Fluid restriction
• B. Hypertonic saline as first line
• C. Isotonic saline infusion
• D. Vasopressin receptor antagonists as initial therapy

Answer: (A)

Fluid restriction is the first-line approach because SIADH causes hyponatremia by retaining free water due to excess ADH, while solute intake and renal function remain normal. Limiting fluid intake reduces the ongoing water load, allowing the kidneys to excrete dilute urine and raise serum sodium gradually and safely in asymptomatic or mildly symptomatic patients. This avoids the risks of rapid correction that can accompany more aggressive therapies. Hypertonic saline is reserved for severe neurologic symptoms (like seizures or coma), not as initial management. Isotonic saline often fails to correct SIADH-related hyponatremia and can worsen it because water retention persists. Vasopressin receptor antagonists are not first-line due to cost, safety concerns, and the potential for overly rapid correction; they’re considered if fluid restriction is insufficient or not feasible.