Q: In Central Nervous System injury, the distinction between Cerebral Salt Wasting(CSW) and SIADH is critically important since both disorders may occur but are managed differently, and choosing wrong algorithm of treatment may be fatal. Which one clinical sign differentiate between CSW and SIADH? 



Answer:  Hypovolemia

Both disease processes in CNS injury shared many similar characteristics like

• The high urine osmolality 
• The urine sodium is usually more than 40 meq/L 
• Serum uric acid concentration is reduced due to urinary loss

Hypovolemia despite significant urinary sodium highly suggests CSW

Treatment of hypovolemia with isotonic saline in CSW helps in resolving the issue but same isotonic saline may worsens the hyponatremia in SIADH.



References:

1. Palmer BF. Hyponatremia in patients with central nervous system disease: SIADH versus CSW. Trends Endocrinol Metab 2003; 14:182. 

2. Maesaka JK, Imbriano LJ, Ali NM, Ilamathi E. Is it cerebral or renal salt wasting? Kidney Int 2009; 76:934.