Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

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Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) by Mind Map: Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

1. Pathophysiology

1.1. Excess secretion of antidiuretic hormone (ADH)

1.1.1. Causes

1.1.1.1. Cancer

1.1.1.1.1. Most Common: Lung

1.1.1.1.2. Oropharynx

1.1.1.1.3. GI Tract

1.1.1.1.4. GU Tract

1.1.1.2. Pulmonary Disease

1.1.1.2.1. Most Common: Infection

1.1.1.2.2. Cystic Fibrosis

1.1.1.3. CNS Disease

1.1.1.3.1. Most Common: Stroke

1.1.1.3.2. Most Common: Infection

1.1.1.3.3. Brain Tumor

1.1.1.4. Drug Side Effects

1.1.1.4.1. Most Common: Antiepileptics

1.1.1.4.2. Most Common: Antidepressants

1.1.1.4.3. Chemotherapy

1.1.1.5. Other Causes

1.1.1.5.1. Most Common: Idiopathic

1.1.1.5.2. Exercise-induced

1.1.1.5.3. Genetic/Hereditary

1.1.1.5.4. AIDS

1.2. ADH acts on renal collecting ducts

1.2.1. Leads to increased renal water reabsorption

1.3. Result is hyponatremia

1.3.1. Result of excess water (dilutional effect)

1.3.2. Not related to sodium deficiency

2. Manifestations

2.1. Primarily related to level of hyponatremia

2.2. Lab Results

2.2.1. Serum Na+ <135 mEq/L

2.2.1.1. 140-130 mEq/L rapid decrease

2.2.1.1.1. thirst

2.2.1.1.2. anorexia

2.2.1.1.3. impaired taste

2.2.1.1.4. exertional dyspnea

2.2.1.1.5. fatigue

2.2.1.2. 130-120 mEq/L

2.2.1.2.1. vomiting

2.2.1.2.2. abdominal cramps

2.2.1.3. <115 mEq/L

2.2.1.3.1. headache

2.2.1.3.2. confusion

2.2.1.3.3. lethargy

2.2.1.3.4. muscle twitches

2.2.1.3.5. seizures

2.2.1.4. <110-115 mEq/L

2.2.1.4.1. severe, possibly irreversible neurologic damage

2.2.2. Serum hypoosmolality

2.2.2.1. <280 mOsm/kg

2.2.3. Urinalysis

2.2.3.1. Elevated osmolality (>100 mOsm/kg)

2.2.3.2. Elevated sodium (>40 mmol/L)

2.3. Physical Exam

2.3.1. Normal BP

2.3.2. Normal skin turgor

2.3.3. No edema present

2.3.4. Euvolemic

3. Diagnostic Criteria (Hoom et al., 2009)

3.1. Euvolemic

3.2. Urine osmolality >100 mOsm/kg

3.2.1. accompanied by serum hypotnicity

3.3. Urine sodium >40 mmol/L

3.3.1. in presence of normal dietary intake

3.4. Normal thyroid & adrenal function

3.5. No presence of:

3.5.1. Recent diuretic use

3.5.2. Renal insufficiency

3.5.3. Heart failure

3.5.4. Other causes of hypovolemia

4. Treatment

4.1. Identify and address underlying etiology

4.2. Address severe hyponatremia

4.2.1. Administer hypertonic fluid (3% NaCl)

4.2.2. Correct imbalance *slowly* to avoid osmotic demyelination syndrome

4.3. Fluid restriction

4.3.1. 800-1,000 mL/day

4.4. Persistent or chronic disease may require pharmaceutical intervention

4.4.1. Loop diuretics (in the presence of hypervolemia)

4.4.2. Vasopressin (parenteral conivaptan or PO tolvaptan)

4.4.3. Osmotic diuretics

4.5. Results

4.5.1. Typically resolved within 3 days with above treatment

4.5.2. 2-3 kg weight loss from water loss

5. References:

5.1. Hoorn, E.J., van der Lubbe, N., & Zietse, R. (2009). SIADH and hyponatremia: Why does it matter? Clinical Kidney Journal, 2(suppl 3), iii5-iii11. doi: 10.1093/ndtplus/sfp153

5.2. McCance, K.L., Huether, S.E., Brashers, V.L., & Rote, N.S. (2014). Pathophysiology: The biologic basis for disease in adults and children. St. Louis, MO: Elsevier.

5.3. Thomas, C.P., Fraer, M., Lederer, E., & Batuman, V. (2014). Syndrome of inappropriate antidiuretic hormone secretion. Retrieved from: http://emedicine.medscape.com/article/246650