What is Causing that Hyponatremia, SIADH vs CSW?

[Pages:1]What is Causing that Hyponatremia, SIADH vs CSW?

S.Sanne DO2, A. Shahzad MD1, M. Hauter MD1, R. Shenava MD3

1Department of Internal Medicine/Pediatrics, 2Department of Internal Medicine, 3Department of Nephrology, LSU-Health Science Center, New Orleans, LA.

IInnttrroodduuccttiioonn

Hyponatremia is a common occurrence after traumatic brain injuries requiring neurosurgical procedures and is most commonly caused by Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH). However, Cerebral Salt Wasting is a rare disorder that produces hyponatremia and can be difficult to distinguish from SIADH.

Case Report

A 31-year old Hispanic man with no past medical history presented after a fall with witnessed seizure and altered mental status. The patient was found to have a small subdural hematoma on the dorsum sella and multiple hemorrhagic contusions. He developed hyponatremia which was thought to be secondary to SIADH but despite fluid restriction, sodium levels remained low. On the ninth hospital day the patient had a serum sodium level of 118 and began having a seizure like episode. A CT scan revealed continued frontotemporal hematoma with surrounding edema and subfalcine herniation. He was sent to surgery for an acute subdural hematoma resection with a frontotemporal craniectomy. The patient was extensively worked up for other causes of hyponatremia, including adrenal, thyroid, and renal dysfunction with unremarkable findings. He was also found to be persistently hypotensive during this period. The patient was started on normal saline and later florinef because of refractory hyponatremia. The patient was diagnosed with cerebral salt wasting syndrome and discharged home on florinef and salt tablets.

Chart

Symptom

BP

Central Venous Pressure

CSWS

Orthostatic Decreased

SIADH

Normal Elevated

Heart Rate

Tachycardia

Serum Osmolality Low

Urine Sodium Levels

High

Tachycardia High High

Urine Volume

High

High

Volume (weight) Decreased

Increased

Treatment

Rehydration and Sodium Replenishment

Fluid Restriction

Key: CSWS= Cerebral salt wasting syndrome. SIADH= Symptom of inappropriate diuretic hormone

Data from Peters JP, Welt LG, Sims EA, Orloff J, Needham J. A Salt-wasting syndrome associated with Cerebral disease. Trans Assoc Am Physicians. 1950.6357-64

Discussion

Challenges exist in differentiating between SIADH and CSW essentially due to the similarities in laboratory data and difficulty in accurately assessing extra-cellular volume status. Differentiation between these two causes of hyponatremia is necessary because of the difference in treatment. Both conditions include a decreased sodium concentration, low to low-normal plasma osmolality and elevated urine osmolality. The difference lies in the mechanism of action of each disorder. SIADH is associated with water retention via ADH effects on the kidney whereas CSW is associated with salt wasting via the kidney. This in essence causes volume expansion/euvolemia in SIADH versus decreased volume in CSW. SIADH will typically have extremely decreased uric acid levels because of decreased absorption secondary to volume expansion and decreased urinary output. In CSW persistent hypotension, elevation in blood urea nitrogen and volume depletion are commonly present. Therefore it is extremely important to monitor the patients volume status to aid when entertaining this diagnosis.

References

1. Maesaka JK, Miyawaki N, Palaia T, Fishbane S, Durham JHC. Renal salt wasting without cerebral disease: Diagnostic value of urate determinations in hyponatremia. Kidney international 2007; 71, 822-826

2. Zafonte RD, Mann NR. Cerebral Salt Wasting Syndrome in Brain Injury Patients: A Potential Cause of Hyponatremia. Arch Phys Med Rehabil 1997; 78, 540-542.

3. Maesaka JK, Imbriano LJ, Ali NM, Ilamathi E. Is it cerebral or renal salt wasting? Kidney International 2009. 76, 934-938.

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