Cerebral Salt-Wasting Syndrome Workup
- Author: Sudha Garimella, MBBS; Chief Editor: Stephen Kemp, MD, PhD more...
Failure to distinguish cerebral salt-wasting syndrome (renal salt wasting) from SIADH as the cause of hyponatremia may lead to improper therapy (ie, fluid restriction), thereby exacerbating intravascular volume depletion and potentially jeopardizing cerebral perfusion.
The following lab studies may be indicated in patients with cerebral salt-wasting syndrome:
Serum sodium concentration - Patients with untreated cerebral salt-wasting syndrome are often hyponatremic
Serum osmolality - If measured serum osmolality exceeds twice the serum sodium concentration and azotemia is not present, suspect hyperglycemia or mannitol as the cause of hyponatremia
Urinary output - Urine is relatively dilute and the flow rate is often high in cerebral salt-wasting syndrome; urine is usually very concentrated and the flow rate is low in SIADH
Urinary sodium concentrations
Urinary sodium concentrations are typically elevated in SIADH and in cerebral salt-wasting syndrome (>40 mEq/L). However, urinary sodium excretion (urinary sodium concentration [mEq/L] x urinary volume [L/24 h]) is substantially higher than sodium intake in cerebral salt-wasting syndrome but generally equals sodium intake in SIADH. Therefore, net sodium balance (intake minus output) is negative in cerebral salt-wasting syndrome.
Fractional Excretion of Uric Acid and Phosphate
Fractional excretion of uric acid (FEUA) is defined as the percentage of urate filtered by glomeruli that is excreted in urine. It is calculated by dividing the product of (urinary uric acid [mg/mL] x serum creatinine [mg/mL]) by the product of (serum uric acid [mg/mL] x urinary creatinine [mg/mL]) and multiplying the result by 100%. Normal values are less than 10%.
Patients with either cerebral salt-wasting syndrome or SIADH can have hypouricemia and elevated FEUA. However, after correction of hyponatremia, hypouricemia and elevated FEUA may normalize in SIADH but persist in cerebral salt-wasting syndrome (renal salt wasting).[3, 4]
Fractional excretion of phosphate (FEP) should be determined when evaluating patients with hyponatremia and hypouricemia. Elevated FEP suggests cerebral salt-wasting syndrome as opposed to SIADH.
Peters JP, Welt LG, Sims EA, et al. A salt-wasting syndrome associated with cerebral disease. Trans Assoc Am Physicians. 1950. 63:57-64. [Medline].
Bettinelli A, Longoni L, Tammaro F, Fare PB, Garzoni L, Bianchetti MG. Renal salt-wasting syndrome in children with intracranial disorders. Pediatr Nephrol. 2012 May. 27(5):733-9. [Medline].
Moritz ML. Syndrome of inappropriate antidiuresis and cerebral salt wasting syndrome: are they different and does it matter?. Pediatr Nephrol. 2012 May. 27(5):689-93. [Medline].
Maesaka JK, Miyawaki N, Palaia T, Fishbane S, Durham JH. Renal salt wasting without cerebral disease: diagnostic value of urate determinations in hyponatremia. Kidney Int. 2007 Apr. 71(8):822-6. [Medline].
Maesaka JK, Imbriano LJ, Ali NM, Ilamathi E. Is it cerebral or renal salt wasting?. Kidney Int. 2009 Nov. 76(9):934-8. [Medline].
Bitew S, Imbriano L, Miyawaki N, Fishbane S, Maesaka JK. More on renal salt wasting without cerebral disease: response to saline infusion. Clin J Am Soc Nephrol. 2009 Feb. 4(2):309-15. [Medline]. [Full Text].
Kao L, Al-Lawati Z, Vavao J, Steinberg GK, Katznelson L. Prevalence and clinical demographics of cerebral salt wasting in patients with aneurysmal subarachnoid hemorrhage. Pituitary. 2009. 12(4):347-51. [Medline].
Kojima J, Katayama Y, Moro N, et al. Cerebral salt wasting in subarachnoid hemorrhage rats: model, mechanism, and tool. Life Sci. 2005 Apr 1. 76(20):2361-70. [Medline].
Rivkees SA. Differentiating appropriate antidiuretic hormone secretion, inappropriate antidiuretic hormone secretion and cerebral salt wasting: the common, uncommon, and misnamed. Curr Opin Pediatr. 2008 Aug. 20(4):448-52. [Medline].
Sherlock M, O'Sullivan E, Agha A, et al. Incidence and pathophysiology of severe hyponatraemia in neurosurgical patients. Postgrad Med J. 2009 Apr. 85(1002):171-5. [Medline].
[Guideline] Rahman M, Friedman WA. Hyponatremia in neurosurgical patients: clinical guidelines development. Neurosurgery. 2009 Nov. 65(5):925-35; discussion 935-6. [Medline].
Brimioulle S, Orellana-Jimenez C, Aminian A, Vincent JL. Hyponatremia in neurological patients: cerebral salt wasting versus inappropriate antidiuretic hormone secretion. Intensive Care Med. 2008 Jan. 34(1):125-31. [Medline].
Cerda-Esteve M, Cuadrado-Godia E, Chillaron JJ, et al. Cerebral salt wasting syndrome: review. Eur J Intern Med. 2008 Jun. 19(4):249-54. [Medline].
Costa KN, Nakamura HM, da Cruz LR, et al. Hyponatremia and brain injury: absence of alterations of serum brain natriuretic peptide and vasopressin. Arq Neuropsiquiatr. 2009 Dec. 67(4):1037-44. [Medline].
Diringer MN, Zazulia AR. Hyponatremia in neurologic patients: consequences and approaches to treatment. The Neurologist. 2006. 12:117-126. [Medline].
Fenske W, Stork S, Koschker AC, et al. Value of fractional uric acid excretion in differential diagnosis of hyponatremic patients on diuretics. J Clin Endocrinol Metab. 2008 Aug. 93(8):2991-7. [Medline].
Frey FJ. [Hyponatraemia in patients with neurosurgical disorders: SIADH or cerebral salt wasting syndrome?]. Ther Umsch. 2009 Nov. 66(11):769-72. [Medline].
Harrigan MR. Cerebral salt wasting syndrome: a review. Neurosurgery. 1996 Jan. 38(1):152-60. [Medline].
Kappy MS, Ganong CA. Cerebral salt wasting in children. Adv Pediatr. 1996. 43:271-308. [Medline].
Levine JP, Stelnicki E, Weiner HL, et al. Hyponatremia in the postoperative craniofacial pediatric patient population: a connection to cerebral salt wasting syndrome and management of the disorder. Plast Reconstr Surg. 2001 Nov. 108(6):1501-8. [Medline].
Lin JJ, Lin KL, Hsia SH, Wu CT, Wang HS. Combined central diabetes insipidus and cerebral salt wasting syndrome in children. Pediatr Neurol. 2009 Feb. 40(2):84-7. [Medline].
Maesaka J, Imbriano L, et al. Cerebral-renal salt wasting. Hyponatremia. New York: EE Simon, Springer; 2013. 65-85.
McGirt MJ, Blessing R, Nimjee SM, et al. Correlation of serum brain natriuretic peptide with hyponatremia and delayed ischemic neurological deficits after subarachnoid hemorrhage. Neurosurgery. 2004. 54:1369-1374. [Medline].
[Guideline] Mentes JC. Hydration management. Iowa City (IA): University of Iowa Gerontological Nursing Interventions Research Center, Research Dissemination Core; 2004 Feb. [Full Text].
Singh S, Bohn D, Carlotti AP, et al. Cerebral salt wasting: truths, fallacies, theories, and challenges. Crit Care Med. 2002 Nov. 30(11):2575-9. [Medline].
Soni SS, Adikey GK, Raman AS. Fractional excretion of uric acid as a therapeutic monitor in cerebral salt wasting syndrome. Saudi J Kidney Dis Transpl. 2008 Jan. 19(1):106-8. [Medline].
Taplin CE, Cowell CT, Silink M, Ambler GR. Fludrocortisone therapy in cerebral salt wasting. Pediatrics. 2006 Dec. 118(6):e1904-8. [Medline].
Janus D, Wojcik M, Dolezal-Oltarzewska K, Kalicka-Kasperczyk A, Poplawska K, Starzyk JB. Cerebral salt wasting in a postoperative period. Neuro Endocrinol Lett. 2014. 35 (4):252-6. [Medline].