From the Guidelines
Syndrome of Inappropriate Antidiuretic Hormone (SIADH) secretion is diagnosed based on euvolemic hypoosmolar hyponatremia and treated with free water restriction and hypertonic saline in severe cases.
Diagnosis
The diagnosis of SIADH is characterized by:
- 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)
- Absence of hypothyroidism, adrenal insufficiency, or volume depletion 1
Treatment
Treatment of SIADH is based on expert opinion and includes:
- Free water restriction (< 1 L/d) as a first-line treatment for asymptomatic mild SIADH and as an adjunct to other therapy for severe cases
- Hypertonic 3% saline IV for life-threatening or acute symptomatic and severe (< 120 mEq/L) hyponatremia
- Demeclocycline, lithium, and vasopressin 2 receptor antagonists (conivaptan, lixivaptan, tolvaptan, and satavaptan) may also be used to correct hyponatremia 1 Key laboratory findings in SIADH include:
- Urine osmolality of > 300 mosm/kg
- Urinary sodium level of > 40 mEq/L
- Serum osmolality of < 275 mosm/kg
- Serum uric acid concentration of < 4 mg/dL 1
From the Research
Diagnosis of SIADH
- The diagnosis of SIADH should be considered if the five cardinal criteria are fulfilled:
- Hypotonic hyponatraemia
- Natriuresis
- Urine osmolality in excess of plasma osmolality
- Absence of oedema and volume depletion
- Normal renal and adrenal function 2
- Diagnosis of SIADH is confirmed by demonstration of a high urine osmolality with a low plasma osmolality, in the absence of diuretic use 3
- Determination of the etiology of SIAD is important because removal of the stimulus for inappropriate arginine vasopressin secretion offers the most effective therapy 4
Treatment of SIADH
- For symptomatic patients with chronic SIADH, the mainstay of therapy remains fluid restriction 2
- Immediate treatment of the symptomatic patient with SIADH includes intravenous furosemide and 3% sodium chloride injection to produce a negative free-water balance 3
- Second-line therapeutic options include loop diuretics and salt tablets, urea, and V2 receptor antagonists 4
- Hypertonic saline remains the gold standard in the initial treatment of symptomatic SIADH with severe neurological deficits, but correction of hyponatremia needs to be slow to avoid osmotic myelinolysis 5
- Vaptans have been shown to be efficacious both during short-term and long-term administration for mild to moderate SIADH with an acceptable safety profile 5