SAH, SIADH and CSW

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Q: Hyponatremia in Subarachnoid hemorrhage (SAH) due to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and cerebral salt wasting can be distinguished by? 

A) level of hyponatremia 

B) serum osmolality

C) urine sodium

D) urine osmolality 

E) intravascular volume status

Answer: E

Hyponatremia in SAH may occur via two mechanisms, i.e., SIADH or cerebral salt wasting. Both are physiologically distinct entities, but hard to differentiate. Both entities have similar levels of hyponatremia, low serum osmolality (<274 mosmol/kg), high urine sodium (>40 mEq/L), and high urine osmolality (>100 mosmol/kg).

  

The major distinguishing feature is intravascular volume status. Patients with SIADH are euvolemic or maybe even hypervolemic. In contrast, patients with cerebral salt wasting tend to be hypovolemic.

  

#electrolytes

#nephrology

#neurology

  

  

References:

  

1. Muehlschlegel S. Subarachnoid Hemorrhage. Continuum (Minneap Minn) 2018; 24:1623.

  

2. Sterns RH, Silver SM. Cerebral salt wasting versus SIADH: what difference? J Am Soc Nephrol. 2008 Feb;19(2):194-6. doi: 10.1681/ASN.2007101118. Epub 2008 Jan 23. PMID: 18216309.