Cerebral salt wasting
1. Cerebral salt wasting (CSW) is best characterised by which of the following primary features?
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CSW is defined by renal loss of sodium after brain injury leading to hypovolemia and hyponatraemia — unlike SIADH which is typically euvolemic.
2. Which clinical sign helps differentiate CSW from SIADH?
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CSW patients are hypovolemic; SIADH patients are typically euvolemic. Volume status assessment is key to differentiation.
3. Which laboratory pattern is most consistent with cerebral salt wasting?
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CSW shows renal salt wasting: high urine sodium and concentrated urine despite low serum sodium due to natriuresis.
4. The most common neurological cause associated with CSW is:
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Subarachnoid haemorrhage is a classic trigger for CSW; other intracranial pathologies (TBI, infections, tumors) can also cause it.
5. Which peptide is implicated in the pathophysiology of CSW by promoting natriuresis?
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Elevated natriuretic peptides (ANP/BNP) after brain injury promote renal sodium loss and contribute to CSW.
6. First-line initial treatment for symptomatic severe hyponatraemia due to CSW is:
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CSW patients need volume and sodium replacement. Severe symptomatic hyponatraemia may require controlled hypertonic saline.
7. Which medication can be used as adjunctive therapy to reduce renal sodium loss in CSW?
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Fludrocortisone promotes sodium retention and can help correct hypovolemia and hyponatraemia in CSW when used with salt/volume replacement.
8. Which of the following is a poor management strategy for CSW?
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Fluid restriction is appropriate for SIADH but harmful in CSW because the patient is hypovolemic and needs sodium/volume repletion.
9. Which haemodynamic parameter is typically low in CSW?
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CSW causes hypovolemia and therefore low CVP and orthostatic signs; SIADH usually has normal CVP.
10. A key diagnostic test that supports CSW over SIADH is:
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CSW corrects with saline because hypovolemia drives ADH release and natriuresis; SIADH does not usually correct with simple saline infusion.
11. Which electrolyte abnormality often accompanies CSW?
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CSW causes hyponatraemia and if prolonged, hypovolemia may lead to reduced renal perfusion and prerenal azotemia.
12. Which of the following statements about urine osmolality in CSW is true?
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Despite hyponatraemia, urine may remain concentrated in CSW because natriuresis and ADH effects can coexist; this contrasts with hypotonic urine expected with simple salt loss.
13. Which of these is an appropriate monitoring parameter during treatment of CSW?
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Close monitoring of serum sodium, urine output, and fluid balance is essential to avoid rapid overcorrection and to guide replacement therapy.
14. Which pharmacologic agent is contraindicated as primary therapy for CSW?
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Vaptans may increase free water excretion but do not address volume depletion and are not the primary therapy in hypovolemic CSW.
15. Which finding on assessment is more typical of SIADH than CSW?
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SIADH patients are typically euvolemic; CSW patients show hypovolemia. This distinction guides management.
16. Which urine sodium value would support a diagnosis of CSW in a hyponatraemic patient?
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A urine sodium >40 mmol/L in a hyponatraemic, hypovolemic patient suggests renal salt wasting such as CSW.
17. Which complication is clinicians most worried about when correcting severe hyponatraemia in CSW?
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Avoid raising serum sodium too quickly; aim for recommended safe rates to prevent central pontine/ osmotic demyelination.
18. Which of the following best describes the role of fludrocortisone in CSW?
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Fludrocortisone mimics aldosterone and enhances sodium reabsorption in the kidney, used when salt/volume replacement alone is insufficient.
19. Which clinical scenario should raise suspicion for CSW?
💬 Show Explanation
Hyponatraemia with renal salt wasting after acute CNS injury (e.g., TBI, SAH) is classic for CSW and should prompt targeted evaluation.
20. Long-term prognosis of CSW depends largely on:
💬 Show Explanation
CSW is secondary to CNS injury; outcomes hinge on the primary brain pathology and appropriate management of volume and sodium disturbances.
| # | Cerebral salt wasting Key Points |
|---|---|
| 1 | Cerebral salt wasting (CSW) is characterized by hyponatremia and hypovolemia, typically following brain injury. |
| 2 | Common triggers include subarachnoid hemorrhage, traumatic brain injury, and intracranial surgery. |
| 3 | Pathophysiology involves excessive natriuresis mediated by brain natriuretic peptides. |
| 4 | Differentiating CSW from SIADH is crucial as treatments differ. |
| 5 | Both CSW and SIADH present with hyponatremia and high urine sodium. |
| 6 | CSW shows hypovolemia, whereas SIADH shows euvolemia or mild hypervolemia. |
| 7 | Volume status assessment is key in distinguishing CSW from SIADH. |
| 8 | CSW results in decreased extracellular fluid volume and hypotension. |
| 9 | Urine output in CSW is typically high due to natriuresis-induced diuresis. |
| 10 | Fractional excretion of sodium (FENa) is usually >2% in CSW. |
| 11 | Plasma uric acid is often low in CSW and remains low after correction of hyponatremia. |
| 12 | CSW treatment focuses on volume and sodium replacement, often with isotonic or hypertonic saline. |
| 13 | Fludrocortisone may be used to reduce urinary sodium loss in refractory CSW cases. |
| 14 | Water restriction is contraindicated in CSW, unlike SIADH. |
| 15 | CSW is more common in pediatric and neurosurgical patients compared to SIADH. |
| 16 | Uncorrected CSW can cause severe dehydration, hypotension, and worsening cerebral ischemia. |
| 17 | Rapid correction of hyponatremia in CSW should be avoided to prevent osmotic demyelination syndrome. |
| 18 | Urine specific gravity is usually high in CSW due to concentrated sodium-rich urine. |
| 19 | Serum BNP levels may be elevated in CSW due to neurohumoral activation. |
| 20 | Long-term follow-up is rarely needed as CSW usually resolves once the brain injury recovers. |
Short Questions & Answers
1. What is cerebral salt wasting?
- CSW is a condition causing excessive renal sodium loss.
- It leads to hyponatremia and dehydration.
- Often associated with brain injury or neurosurgery.
- Results from increased natriuretic peptide activity.
- Distinguished from SIADH by volume status.
2. What are the key causes of CSW?
- Subarachnoid hemorrhage.
- Traumatic brain injury.
- Brain tumors or surgery.
- Central nervous system infections.
- Stroke or intracerebral hemorrhage.
3. How does CSW differ from SIADH in volume status?
- CSW patients are hypovolemic.
- SIADH patients are euvolemic or slightly hypervolemic.
- Both present with hyponatremia.
- Volume status is a key differentiator.
- Clinical exam and labs confirm status.
4. What is the mechanism of sodium loss in CSW?
- Increased natriuretic peptide secretion.
- Decreased renal sodium reabsorption.
- Increased urine sodium excretion.
- Water loss follows sodium loss.
- Leads to hypovolemia and hyponatremia.
5. What are the clinical signs of CSW?
- Hypotension.
- Tachycardia.
- Poor skin turgor.
- Dry mucous membranes.
- Lethargy or confusion.
6. How is CSW diagnosed?
- History of CNS insult.
- Hyponatremia with high urine sodium (>40 mmol/L).
- High urine output (polyuria).
- Low serum osmolality.
- Evidence of hypovolemia.
7. What is the primary treatment for CSW?
- Sodium replacement.
- Volume expansion with isotonic saline.
- In severe cases, hypertonic saline.
- Monitor serum sodium closely.
- Treat underlying brain pathology.
8. What is the role of fludrocortisone in CSW?
- Synthetic mineralocorticoid.
- Enhances sodium reabsorption in kidneys.
- Reduces urinary sodium losses.
- Used in persistent cases.
- Adjunct to fluid and sodium therapy.
9. What complications can arise from untreated CSW?
- Severe dehydration.
- Hypotensive shock.
- Worsening cerebral perfusion.
- Electrolyte imbalance complications.
- Death in extreme cases.
10. How can CSW be prevented in high-risk patients?
- Early monitoring of electrolytes post-CNS injury.
- Regular assessment of volume status.
- Prompt replacement of sodium losses.
- Avoid over-restricting fluids unnecessarily.
- Early involvement of neurology and nephrology teams.
Cerebral Salt Wasting (CSW) is a rare but serious cause of hyponatremia that often occurs after brain injury, neurosurgery, or central nervous system diseases. It is characterized by excessive loss of sodium in urine, leading to hypovolemia and dehydration. Unlike Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH), where fluid retention is common, CSW patients are volume-depleted.
Prompt recognition and treatment are essential to prevent complications such as hypotension, cerebral hypoperfusion, and even death. This guide covers the causes, pathophysiology, clinical features, diagnosis, and management of CSW, along with a comparison to SIADH for accurate differentiation.
| Feature | Cerebral Salt Wasting (CSW) | SIADH |
|---|---|---|
| Primary Cause | Brain injury, subarachnoid hemorrhage, CNS infection, neurosurgery | Increased ADH secretion due to CNS disorders, lung disease, drugs |
| Volume Status | Hypovolemic | Euvolemic or slightly hypervolemic |
| Pathophysiology | Loss of sodium in urine due to impaired renal sodium handling | Water retention due to inappropriate ADH secretion |
| Serum Sodium | Low (hyponatremia) | Low (hyponatremia) |
| Serum Osmolality | Low | Low |
| Urine Sodium | High (>40 mmol/L) | High (>40 mmol/L) |
| Urine Osmolality | High | High |
| Plasma Volume | Decreased | Normal or increased |
| ADH Levels | Normal or low | Inappropriately high |
| Treatment | Volume replacement with isotonic/hypertonic saline, salt tablets | Fluid restriction, ADH antagonists, hypertonic saline if severe |
