How should I approach the management of a patient with SIADH who presents with mild hyponatremia?

For a patient with syndrome of inappropriate antidiuretic hormone secretion (SIADH) presenting with mild hyponatremia (serum sodium concentration of 130–135 mmol/L), the management approach in General Practice should involve several key steps.

• Initial Assessment and Monitoring: Ensure a repeat serum sodium measurement has been taken to rule out a rapidly decreasing serum sodium concentration, as this would necessitate immediate hospital admission ¹. Asymptomatic, mild hyponatremia (130–135 mmol/L) may initially be managed in primary care ¹.
• Fluid Restriction: Fluid restriction is a recommended management strategy for people with SIADH ¹.
• Medication Review: Stop any non-essential medications that may be contributing to the hyponatremia, if appropriate, and recheck the serum sodium concentration after two weeks ¹. If a contributing medication cannot be stopped, contact the appropriate specialist to discuss further management, monitoring, or referral ¹.
• Treat Underlying Causes: If an acute illness is contributing to the hyponatremia, treat the underlying problem and recheck the serum sodium concentration after two weeks or sooner based on clinical judgment ¹.
• Referral Considerations:
  • Discuss with an endocrinologist about the need for admission or referral if the person has asymptomatic, moderate hyponatremia (serum sodium concentration of 125–129 mmol/L) ¹.
  • Refer to an endocrinologist if SIADH or another endocrine cause is suspected, with the urgency depending on clinical judgment ¹. Specialist input is required to confirm the diagnosis and initiate treatment for hyponatremia related to an endocrine disorder ¹.
  • Arrange an urgent 2-week wait referral to the appropriate specialist if malignant disease is suspected as an underlying cause of SIADH ¹.
  • Tolvaptan, a medication for hyponatremia secondary to SIADH, should only be initiated in hospital or under specialist supervision ¹.