Diagnosis and Management of Cerebral Salt Wasting, Nephrogenic Diabetes Insipidus, SIADH, and Interstitial Nephritis
Cerebral Salt Wasting (CSW) Diagnosis and Management
Cerebral salt wasting should be treated with sodium and volume replacement, not fluid restriction, as this can worsen outcomes. 1
Diagnosis
- CSW is characterized by hyponatremia, evidence of extracellular volume depletion (hypotension, tachycardia, dry mucous membranes), and inappropriately high renal sodium loss (typically >20 mmol/L) 2, 3
- 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 4
- CSW is more common in patients with poor clinical grade, ruptured anterior communicating artery aneurysms, and hydrocephalus 2
Management
- Treatment focuses on volume and sodium replacement through isotonic or hypertonic saline administration based on severity 1, 5
- Aggressive volume resuscitation with crystalloid or colloid agents can reduce the risk of cerebral ischemia 2
- Fludrocortisone (mineralocorticoid) at doses of 0.1-0.4 mg daily has shown benefit in managing CSW 6, 7
- 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
- In severe cases requiring large volumes of hypertonic saline, fludrocortisone can reduce the amount of hypertonic saline needed 5
Nephrogenic Diabetes Insipidus (NDI) Diagnosis and Management
NDI management requires a multidisciplinary approach including a nephrologist, dietitian, psychologist, social worker, and urologist to address the complex nature of the condition. 8
Diagnosis
- Characterized by inability of the kidneys to respond to ADH, resulting in hypotonic polyuria and potential hypernatremia 9
- Diagnostic gold standard is a water deprivation test followed by desmopressin administration 9
- Urine osmolality testing can help assess for secondary NDI 8
- Copeptin (a surrogate marker of ADH) may simplify and improve diagnostic accuracy in the future 9
Management
- 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
- 1-3 years: 2g/day salt, 1.1 g/kg/day protein
- 4-6 years: 3g/day salt, 0.95 g/kg/day protein
- 7-10 years: 5g/day salt, 0.95 g/kg/day protein
11 years: <6g/day salt, 0.85 g/kg/day protein
- Adults: <6g/day salt, <1 g/kg/day protein 8
- Medications to reduce polyuria include:
- Thiazide diuretics (with reduced sodium intake)
- Amiloride (often combined with thiazides)
- Prostaglandin synthesis inhibitors
- Selective COX-2 inhibitors like celecoxib 8
- Ensure adequate access to water at all times 9
- Monitor for hydronephrosis with kidney ultrasound at least every 2 years 8
- Regular follow-up schedule:
- Infants: Every 2-3 months
- Children: Every 3-12 months
- Adults: Annually 8
- COX inhibitors should be discontinued once patients reach adulthood (≥18 years) or earlier if full continence is achieved 8
SIADH Pathophysiology and Management
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. 4, 1
Pathophysiology
- Excessive secretion of antidiuretic hormone (ADH) leads to water retention and dilutional hyponatremia 4
- Common causes include:
- CNS disorders (tumors, trauma, infection)
- Pulmonary disorders (pneumonia, tuberculosis)
- Malignancies (especially small cell lung cancer)
- Medications (chemotherapeutic agents, antidepressants, antiepileptics, NSAIDs, opioids) 4
- Results in impaired free water excretion despite hypo-osmolality 4
Diagnosis
- Diagnostic criteria include:
- Hyponatremia (serum sodium <134 mEq/L)
- Hypoosmolality (plasma osmolality <275 mosm/kg)
- Inappropriately high urine osmolality (>500 mosm/kg)
- Inappropriately high urinary sodium concentration (>20 mEq/L)
- Euvolemic state (absence of clinical signs of hypovolemia or hypervolemia)
- Normal renal, adrenal, and thyroid function 4
- Serum uric acid <4 mg/dL has a positive predictive value of 73-100% for SIADH 4
Management
- For severe symptomatic hyponatremia:
- For mild symptomatic or asymptomatic hyponatremia:
- Desmopressin is contraindicated in SIADH as it can worsen hyponatremia 10
- Treat underlying cause when possible, especially in paraneoplastic SIADH 4
Interstitial Nephritis Diagnosis
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.
Diagnosis
- Clinical features include:
- Fever
- Rash
- Eosinophilia
- Eosinophiluria
- Sterile pyuria
- Proteinuria (typically <1g/day)
- Elevated serum creatinine
- Common causes:
- Drug-induced (antibiotics, NSAIDs, proton pump inhibitors)
- Autoimmune diseases (lupus, Sjögren's syndrome)
- Infections (streptococcal, viral, tuberculosis)
- Definitive diagnosis requires kidney biopsy showing interstitial inflammation and tubulitis
- Urinalysis typically shows white blood cells, white blood cell casts, and sometimes red blood cells
Common Pitfalls to Avoid
- 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 4, 1
- Inadequate monitoring during active correction of hyponatremia 1
- Failing to recognize and treat the underlying cause of SIADH or interstitial nephritis 4, 1
- Using desmopressin in patients with SIADH, as it is contraindicated and can worsen hyponatremia 10