Makindo Medical Notes

Both SIADH and CSW present with hyponatraemia and high urine sodium. 🔑 Key difference = **Volume status**: - CSW → Hypovolaemic 💧 - SIADH → Euvolaemic/Hypervolaemic ⚖️

🧠 About

• Cerebral Salt Wasting (CSW) is a condition in which cerebral injury leads to inappropriate renal sodium loss.
• This sodium loss causes water loss → hypovolaemia + hyponatraemia.
• SIADH differs because the patient is euvolaemic or hypervolaemic → here, management is fluid restriction, not replacement.
• Clinical importance: misdiagnosis can worsen hyponatraemia — e.g. fluid restriction in CSW can be dangerous ❌.

⚠️ Aetiology

• Increased release of cerebral natriuretic peptides after CNS injury.
• Sympathetic dysfunction affecting renal sodium handling.
• Common triggers: Subarachnoid haemorrhage (SAH), traumatic brain injury, intracranial surgery, meningitis, encephalitis.

👩‍⚕️ Clinical Features

• Often occurs in patients with head injury or SAH.
• Polyuria (>2.5 L/day).
• Features of volume depletion:
  • Hypotension
  • Tachycardia
  • Dehydrated mucous membranes
• Contrast: SIADH patients look euvolaemic.

🧪 Investigations

• Serum sodium: Low (<134 mmol/L).
• Serum osmolality: Low.
• Urine osmolality: Raised (inappropriately concentrated).
• Urine sodium: >20 mmol/L (usually higher than SIADH).
• Urine output: Often >2500 mL/day.

📊 CSW vs SIADH (Key Differences)

💊 Management

• CSW: Treat with fluid + sodium replacement (opposite of SIADH!).
• Options:
  • IV 0.9% saline or 3% hypertonic saline for severe cases.
  • Fludrocortisone may be used to reduce natriuresis.
• SIADH: Managed by fluid restriction — highlighting the danger of misdiagnosis.

📚 References

• Cerebral Salt Wasting Syndrome: Review
• Cerebral salt wasting vs SIADH – practical differentiation (Nephrol Dial Transplant)