Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a disorder with impaired water excretion (concentrated urine), caused by abnormal production of antidiuretic hormone (ADH) despite low serum osmolality.
- Decreased urinary electrolyte-free water excretion leads to dilutional hyponatremia (total body sodium [Na] levels may be normal or near-normal, but the patient’s total body water is increased).
- Often secondary to medications but may be associated with an underlying disorder, such as neoplasm, a pulmonary disorder, or central nervous system (CNS) disease
- Common cause of hyponatremia in hospitalized patients
- Synonym(s): syndrome of inappropriate secretion of ADH; syndrome of inappropriate antidiuresis
- Often found in the hospital setting, especially perioperative patients in response to stress, hypotonic fluids, and drugs; the incidence can be as high as 35%.
- Predominant age: elderly
- Predominate sex: females > males
Etiology and Pathophysiology
- Antidepressants (e.g., SSRIs, tricyclics, monoamine oxidase inhibitors [MAOIs])
- Antineoplastic drugs (e.g., vincristine, vinblastine, cisplatin, cyclophosphamide)
- Antipsychotic agents (e.g., risperidone, quetiapine, phenothiazine, haloperidol)
- Analgesics (e.g., duloxetine, pregabalin, tramadol, NSAIDs)
- Anticonvulsants (e.g., carbamazepine, oxcarbazepine, valproic acid, phenytoin)
- Others (e.g., vasopressin, DDAVP, oxytocin, ciprofloxacin, α-interferon, ecstasy)
- Malignancies (ectopic ADH production):
- Bronchogenic or small cell carcinoma of the lung
- Pancreatic adenocarcinoma
- Pulmonary conditions:
- Cystic fibrosis
- Positive pressure mechanical ventilation
- Pneumonia (viral, bacterial)
- Pulmonary tuberculosis (TB)
- Neurologic causes:
- Brain tumor
- CNS injury (i.e., subarachnoid hemorrhage, trauma, stroke, surgery)
- CNS lupus
- Encephalitis, meningitis
- Guillain-Barré syndrome
- Multiple sclerosis
- Acute intermittent porphyria
- Delirium tremens
- HIV infection/AIDS
- Rocky Mountain spotted fever
- 10% of patients have an X-linked mutation of vasopressin V2 receptor (V2R).
- Polymorphisms in TRPV4 gene
- Advanced age
- Postoperative status
- Use of predisposing drugs
- Reduce/change medications, if drug induced.
- Lifelong restriction of fluid intake
Commonly Associated Conditions
See “Etiology and Pathophysiology.”
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