SIADH: Diagnosis and Management
Micro-brief créé avec inScope · Relu cliniquement par Yasmine Abbey, MD, MSc · Dernière relecture:
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L'essentiel
SIADH is a diagnosis of exclusion in a euvolemic patient with hypotonic hyponatremia. When there are no severe symptoms, fluid restriction (commonly 800–1000 mL/day) is first-line, alongside stopping ADH-stimulating drugs and treating the underlying cause.
Severe neurologic symptoms (seizure, obtundation) or a very low sodium call for cautious 3% hypertonic saline boluses aiming to raise serum sodium by 4–6 mmol/L, then reassessment — while keeping the 24-hour rise under 8–10 mmol/L to avoid osmotic demyelination.
Initial workup
- Confirm hypotonic hyponatremia: serum osmolality < 275 mOsm/kg with serum sodium < 135 mmol/L.
- Urine studies: urine osmolality > 100 mOsm/kg and urine sodium > 30 mmol/L, demonstrating inappropriate concentration and sodium loss.
- Exclude other causes: confirm euvolemia, obtain TSH and a morning cortisol (± cosyntropin) to rule out thyroid and adrenal insufficiency, and review renal function and the medication list for offending drugs.
- Identify reversible triggers — pulmonary or CNS disease, malignancy, and drugs — with appropriate imaging or labs.
Acute management
- For severe neurologic symptoms or a very low sodium, give a cautious 3% hypertonic saline bolus aiming to raise serum sodium by 4–6 mmol/L, then reassess and repeat if needed.
- Otherwise begin first-line fluid restriction (commonly 800–1000 mL/day).
- Discontinue or reduce medications that stimulate ADH (e.g., SSRIs, carbamazepine, thiazides).
- Check serum sodium frequently (every 4–6 hours initially) to pace correction and avoid rapid overcorrection.
Inpatient and longitudinal management
- If sodium fails to improve with fluid restriction (roughly half of cases), consider second-line options: a vasopressin-2 receptor antagonist (tolvaptan), oral urea, or an SGLT2 inhibitor.
- Consider a loop diuretic plus oral salt tablets in patients with high urine osmolality who cannot tolerate fluid restriction.
- Treat the underlying etiology (e.g., tumor resection, treatment of infection).
- Educate on fluid targets and signs of relapse, and arrange endocrinology or nephrology follow-up if chronic.
Monitoring and disposition
- Track serum sodium and osmolality at least every 4–6 hours during active correction, then daily once stable.
- Monitor urine output and electrolytes to detect aquaresis when vaptans are used.
- Provide ICU-level care for patients receiving hypertonic saline boluses or with seizures; step down to the ward once neurologically stable and sodium is rising slowly.
- Discharge when sodium is stable on an oral regimen or fluid restriction, symptoms have resolved, and the cause is addressed; arrange an outpatient sodium check within a week.
Escalate care if
- Serum sodium falls below 120 mmol/L or neurologic symptoms develop — move to ICU care and initiate a hypertonic saline bolus protocol.
- Overcorrection greater than 8–10 mmol in 24 hours is suspected — stop active therapy and consider desmopressin with free-water replacement.
- Disease is refractory to second-line pharmacotherapy or recurrent — consult nephrology or endocrinology for demeclocycline or long-term vaptan therapy.
Duration
Continue fluid restriction until the underlying cause resolves or sodium normalizes; reassess pharmacologic agents daily and taper once sodium is stable.
Mises en garde
- Avoid rapid sodium correction (greater than 8–10 mmol/24 h) — it risks osmotic demyelination.
- Tolvaptan is contraindicated in anuric patients and in significant hepatic impairment (consult product labeling).
Références
- Syndrome of Inappropriate Antidiuresis (clinical overview). · Recommandation officielle“In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines.”
- Syndrome of Inappropriate Antidiuresis. Endocr Rev. · Revue systématique“The presence of severe symptoms should prompt treatment with careful bolus hypertonic saline aiming for an increment in serum sodium of 4 to 6 mmol.”
- Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): Optimal Management. · Source primaire“SIADH diagnosis is still a diagnosis of exclusion and the criteria are the same initially described by Bartter and Schwartz in 1957.”