Cerebral Salt Wasting, Nephrogenic Diabetes Insipidus, SIADH, and Interstitial Nephritis Management

Diagnosis and Management of Cerebral Salt Wasting (CSW)

Cerebral salt wasting should be treated with sodium and volume replacement, not fluid restriction, as this can worsen outcomes 1
CSW is characterized by hyponatremia, evidence of extracellular volume depletion, and inappropriately high renal sodium loss (typically >20 mmol/L) 2
High urine osmolality relative to serum osmolality is a characteristic finding 2
Differentiation from SIADH is critical as treatment approaches differ significantly 1
Central venous pressure (CVP) can help distinguish: CSW typically has CVP <6 cm H₂O versus SIADH with CVP 6-10 cm H₂O 3
CSW is more common in patients with poor clinical grade, ruptured anterior communicating artery aneurysms, and hydrocephalus 2
Treatment focuses on volume and sodium replacement through isotonic or hypertonic saline administration based on severity 1
Aggressive volume resuscitation with crystalloid or colloid agents can reduce the risk of cerebral ischemia 2
Hydrocortisone may be used to prevent natriuresis in subarachnoid hemorrhage patients 1
Monitor serum sodium levels closely, with correction not exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1

NDI management requires a multidisciplinary approach including a nephrologist, dietitian, psychologist, social worker, and urologist to address the complex nature of the condition 4
Urine osmolality testing can help assess for secondary NDI 5
Dietary salt and protein recommendations should be followed based on age:
- 0-1 year: 1g/day salt, 1.3-1.8 g/kg/day protein 4
- 1-3 years: 2g/day salt, 1.1 g/kg/day protein 4
- 4-6 years: 3g/day salt, 0.95 g/kg/day protein 4
- 7-10 years: 5g/day salt, 0.95 g/kg/day protein 4
- >11 years: <6g/day salt, 0.85 g/kg/day protein 4
- Adults: <6g/day salt, <1 g/kg/day protein 4
Medications to reduce polyuria include thiazide diuretics, amiloride, prostaglandin synthesis inhibitors, and selective COX-2 inhibitors like celecoxib 4
Ensure adequate access to water at all times
Monitor for hydronephrosis with kidney ultrasound at least every 2 years 4
Regular follow-up schedule:
- Infants: Every 2-3 months 5
- Children: Every 3-12 months 5
- Adults: Annually 4
COX inhibitors should be discontinued once patients reach adulthood (≥18 years) or earlier if full continence is achieved 4

SIADH is characterized by hyponatremia with inappropriate urinary concentration in a euvolemic patient, and fluid restriction to 1L/day is the cornerstone of treatment for mild to moderate cases 3, 1
Excessive secretion of antidiuretic hormone (ADH) leads to water retention and dilutional hyponatremia 3
Common causes include pulmonary disorders, malignancies, and medications 2, 3
Diagnostic criteria include hyponatremia, hypoosmolality, inappropriately high urine osmolality, and inappropriately high urinary sodium concentration 3, 1
For severe symptomatic hyponatremia, administer 3% hypertonic saline with goal to correct 6 mmol/L over 6 hours or until severe symptoms resolve 2
Monitor serum sodium every 2 hours initially 3, 1
Total correction should not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 3, 1
For mild symptomatic or asymptomatic hyponatremia, fluid restriction to 1 L/day is recommended 3, 1
Consider pharmacological options for resistant cases, including urea, diuretics, demeclocycline, lithium, and vasopressin receptor antagonists 1, 3

Interstitial nephritis diagnosis requires a high index of suspicion and should be considered in patients with acute kidney injury, especially when associated with drug exposure, systemic diseases, or infections
Clinical features include fever, proteinuria, and elevated serum creatinine 5, 4
Common causes include drug-induced, autoimmune diseases, and infections 3, 5
Definitive diagnosis requires kidney biopsy showing interstitial inflammation and tubulitis 3
Urinalysis typically shows white blood cells, white blood cell casts, and sometimes red blood cells 1

Failing to distinguish between CSW and SIADH, as treatments are diametrically opposed 1
Using fluid restriction in CSW, which can worsen outcomes 1
Overly rapid correction of hyponatremia (>8 mmol/L in 24 hours), risking osmotic demyelination syndrome 3, 1
Inadequate monitoring during active correction of hyponatremia 1
Failing to recognize and treat the underlying cause of SIADH or interstitial nephritis 3, 1