Syndrome of inappropriate antidiuresis and cerebral salt wasting syndrome: are they different and does it matter?

Cerebral salt wasting syndrome in an elderly patient with cerebral small vessel disease

Hyponatremia is a common electrolyte disturbance seen among the acute geriatric admissions with two common diagnostic entities; the syndrome of inappropriate antidiuretic hormone (SIADH) and cerebral salt wasting syndrome (CSWS) that have different clinical and biochemical presentations, different pathogenesis and therapeutic approaches. Hyponatremia caused by CSWS in patients with cerebral small vessel disease (cSVD) a prevalent condition among the elderly, can be masked in geriatric patients with concomitant fluctuating neurological deficits. Correct diagnosis is crucial to appropriate management. In this case report we describe an association between hyponatremia caused by CSWS in a patient with cSVD.

Severe symptomatic hyponatremia due to cerebral salt wasting syndrome in a patient with traumatic head injury and Dandy-Walker malformation of the brain

Cerebral salt wasting (CSW) is an uncommon cause of hyponatremia characterized by extracellular volume depletion, high urine sodium concentration and osmolality, and low serum uric acid concentration in association with central nervous system (CNS) disease. Distinguishing CSW from the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), a much more common form of hyponatremia in this setting, can be challenging because both present with identical laboratory features. However, treatment of CSW and SIADH differs, making a correct diagnosis important. Here we present a case of CSW in a 75-year-old man in whom severe hyponatremia and volume depletion were discovered in the setting of traumatic head injury and Dandy-Walker malformation of the brain, a rare congenital brain malformation. Treatment with intravenous normal saline and later oral salt supplementation and fludrocortisone was successful.

An Integrative Review of Cerebral Salt Wasting Syndrome

BACKGROUND

Although cerebral salt wasting syndrome (CSWS) is widely recognized, its clinical characteristics, diagnostic criteria, and management have not been clearly defined. This study was undertaken to comprehensively review current literature and provide a more complete picture of CSWS. This review also aimed to provide information for nurses on how to differentiate cerebral salt wasting syndrome from syndrome of inappropriate antidiuretic hormone secretion.

METHODS

An integrative review was performed. Searches were conducted between May and July 2018. The primary information sources were CINAHL, Google Scholar, MEDLINE, PubMed, Scopus, and Web of Science. Included articles were published from 1954 to July 2018.

RESULTS

The essential features of CSWS are hyponatremia, hypovolemia, and increased urine output. Treatment regimens may be determined based on the acuity and severity of hyponatremia and hypovolemia as well as evident symptoms and signs.

CONCLUSION

This review may help neuroscience nurses become knowledgeable about CSWS for the drafting of appropriate nursing care plans and also be able to differentiate CSWS from syndrome of inappropriate antidiuretic hormone secretion as early as possible for timely and proper management.

Syndrome of Inappropriate Antidiuresis

The syndrome of inappropriate antidiuresis (SIAD) is a common cause of hyponatremia in hospitalized children. SIAD refers to euvolemic hyponatremia due to nonphysiologic stimuli for arginine vasopressin production in the absence of renal or endocrine dysfunction. SIAD can be broadly classified as a result of tumors, pulmonary or central nervous system disorders, medications, or other causes such as infection, inflammation, and the postoperative state. The presence of hypouricemia with an elevated fractional excretion of urate can aid in the diagnosis. Treatment options include fluid restriction, intravenous saline solutions, oral sodium supplements, loop diuretics, oral urea, and vasopressin receptor antagonists (vaptans).

[A case of cerebral salt wasting syndrome caused by minor head injury]

An 80-year-old woman who was hospitalized due to small subarachnoid hemorrhaging caused by a bruise in the left temporal region of the brain. Nausea/vomiting and malaise appeared after dinner on the fourth day of the illness. Head computed tomography showed that the post-traumatic status was almost normal; however, the sodium ion (Na⁺) level was 114 mEq/L, indicating severe hyponatremia. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) following a head injury was initially suspected, and water restriction and saline fluid replacement were initiated. However, the Na⁺ level did not improve, and signs of dehydration emerged. On the seventh day of the illness, drinking water restriction was discontinued, and 3% sodium chloride fluid replacement was initiated. The patient subsequently followed a favorable course, and the Na⁺ level remained normal even after fluid replacement was discontinued. It is important to differentiate between SIADH and cerebral salt wasting syndrome (CSWS), as the treatment of the two are diametrically opposite. However, distinguishing between these two diseases at an early onset can be difficult, as they have very similar laboratory findings. CSWS can occur in patients with minor head injury, as in the present case, so we should bear this disease in mind as a differential diagnosis, even when imperceptible graduations are recognized in patients.

Syndrome of inappropriate antidiuretic hormone secretion and cerebral/renal salt wasting syndrome: similarities and differences

Hyponatremia (sodium levels of <135 mEq/L) is one of the most common electrolyte imbalances in clinical practice, especially in patients with neurologic diseases. Hyponatremia can cause cerebral edema and brain herniation; therefore, prompt diagnosis and proper treatment is important in preventing morbidity and mortality. Among various causes of hyponatremia, diagnosing syndrome of inappropriate antidiuretic hormone secretion (SIADH) and cerebral/renal salt wasting syndrome (C/RSW) is difficult due to many similarities. SIADH is caused by excess of renal water reabsorption through inappropriate antidiuretic hormone secretion, and fluid restriction is the treatment of choice. On the other hand, C/RSW is caused by natriuresis, which is followed by volume depletion and negative sodium balance and replacement of water and sodium is the mainstay of treatment. Determinating volume status in hyponatremic patients is the key point in differential between SIADH and C/RSW. However, in most situations, differential diagnosis of these two diseases is difficult because they overlap in many clinical and laboratory aspects, especially to assess differences in volume status of these patients. Although distinction between the SIADH and C/RSW is difficult, improvement of hypouricemia and an increased fractional excretion of uric acid after the correction of hyponatremia in SIADH, not in C/RSW, may be one of the helpful points in discriminating the two diseases. In this review, we compare these two diseases regarding the pathophysiologic mechanisms, diagnosis, and therapeutic point of view.

Management of hyponatremia in various clinical situations

OPINION STATEMENT

Hyponatremia is the most common electrolyte abnormality in both inpatient and outpatient settings. The condition primarily results from the combination of impaired free water excretion due to elevated vasopressin levels in conjunction with a source of free water intake. Recent studies have revealed that even mild and asymptomatic hyponatremia is associated with deleterious consequences. It is an independent risk factor for mortality and is also associated with increased length of hospitalization and hospital costs. Even mild chronic hyponatremia can result in subtle neurologic impairment and bone demineralization, leading to falls and associated bone fractures in the elderly. Hyponatremia can be a difficult condition to treat, with varying therapeutic strategies based on the etiology, severity, duration, and extent of neurologic symptoms. The ideal magnitude of correction is also controversial, as both inadequate therapy and overly aggressive therapy can result in neurologic injury. Formulas that have been devised to aid in the treatment of hyponatremia can be inaccurate in that they fail to adequately account for the renal response to therapy. Hyponatremic encephalopathy is the most serious complication of hyponatremia, and can result in permanent neurologic impairment or death if left untreated. Individuals most at risk for developing hyponatremic encephalopathy are postmenarchal women, children under 16 years of age, patients with central nervous system disease or hypoxemia, and patients in the postoperative setting. The preferred therapy for hyponatremic encephalopathy is a 100-ml bolus of 3 % sodium chloride (513 mEq/L) administered in repeated doses until symptoms reverse, with the goal of increasing the serum sodium 5-6 mEq/L. Vasopressin (V2) antagonists (vaptans) are not appropriate for the management of acute hyponatremic encephalopathy, as the onset of action is not sufficiently rapid and the increase in sodium is not predictable. Vaptans are primarily indicated for the treatment of asymptomatic hyponatremia due to SIAD that is refractory to conventional measures.

Phage display generation of a novel humanized single-chain antibody against brain natriuretic peptide with potent neutralizing activity

Cerebral salt wasting syndrome (CSW) is defined as a renal loss of sodium and water during intracranial disease leading to hyponatremia, which is the most frequent electrolyte disorder in critically neurological patients. Abnormal brain natriuretic peptide (BNP) secretion is implicated as the main offender. Development of antagonist against BNP is therefore of potential clinical relevance. In this study, synthetic human BNP peptide (hBNP) was used as bait and a humanized single chain fragment variable (scFv) phage antibody library as the source of antagonists. After three rounds of biopanning, hBNP-specific phage clones were greatly enriched. The scFv gene from the best phage clone was inserted into pET-22b and expressed in Escherichia coli BL21 (DE3) PlysS cells. After purification by nickel-affinity and refolding, this scFv antibody (Ab) was proven to recognize hBNP specifically and sensitively in ELISA and dot-blotting assay. Its binding constant to hBNP was 1.98×10(-8) M, measured by surface plasmon resonance. Thus, the humanized scFv Ab prepared with this approach has potential therapeutic value for neutralizing abnormally high level of BNP correlated well with CSW.

Clinical review: practical approach to hyponatraemia and hypernatraemia in critically ill patients

Disturbances in sodium concentration are common in the critically ill patient and associated with increased mortality. The key principle in treatment and prevention is that plasma [Na+] (P-[Na+]) is determined by external water and cation balances. P-[Na+] determines plasma tonicity. An important exception is hyperglycaemia, where P-[Na+] may be reduced despite plasma hypertonicity. The patient is first treated to secure airway, breathing and circulation to diminish secondary organ damage. Symptoms are critical when handling a patient with hyponatraemia. Severe symptoms are treated with 2 ml/kg 3% NaCl bolus infusions irrespective of the supposed duration of hyponatraemia. The goal is to reduce cerebral symptoms. The bolus therapy ensures an immediate and controllable rise in P-[Na+]. A maximum of three boluses are given (increases P-[Na+] about 6 mmol/l). In all patients with hyponatraemia, correction above 10 mmol/l/day must be avoided to reduce the risk of osmotic demyelination. Practical measures for handling a rapid rise in P-[Na+] are discussed. The risk of overcorrection is associated with the mechanisms that cause hyponatraemia. Traditional classifications according to volume status are notoriously difficult to handle in clinical practice. Moreover, multiple combined mechanisms are common. More than one mechanism must therefore be considered for safe and lasting correction. Hypernatraemia is less common than hyponatraemia, but implies that the patient is more ill and has a worse prognosis. A practical approach includes treatment of the underlying diseases and restoration of the distorted water and salt balances. Multiple combined mechanisms are common and must be searched for. Importantly, hypernatraemia is not only a matter of water deficit, and treatment of the critically ill patient with an accumulated fluid balance of 20 litres and corresponding weight gain should not comprise more water, but measures to invoke a negative cation balance. Reduction of hypernatraemia/hypertonicity is critical, but should not exceed 12 mmol/l/day in order to reduce the risk of rebounding brain oedema.