From the Guidelines
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is primarily caused by excessive release of antidiuretic hormone (ADH) from the posterior pituitary gland or from ectopic sources, leading to water retention and hyponatremia, as supported by the most recent evidence 1. The most common causes of SIADH include:
- Central nervous system disorders (such as stroke, meningitis, brain tumors, or head trauma)
- Pulmonary diseases (particularly small cell lung cancer, pneumonia, and tuberculosis)
- Certain medications, such as:
- Antidepressants (especially SSRIs like fluoxetine and sertraline)
- Antipsychotics
- Anticonvulsants (carbamazepine)
- Chemotherapy agents (cyclophosphamide, vincristine)
- Opioids Other causes include endocrine disorders (hypothyroidism, adrenal insufficiency), pain, nausea, and major surgery. The excessive ADH causes increased water reabsorption in the kidneys' collecting ducts, resulting in dilutional hyponatremia while maintaining normal extracellular fluid volume, as explained in the guidelines for liver cirrhosis management 1. Treatment of SIADH depends on identifying and addressing the underlying cause while managing the hyponatremia through fluid restriction, salt supplementation, or in severe cases, administration of vasopressin receptor antagonists like tolvaptan, which has been shown to be effective in improving serum sodium concentration in patients with SIADH, heart failure, or cirrhosis 1.
From the Research
Causes of SIADH
- SIADH is often associated with small cell lung cancer (SCLC), with approximately 11%-15% of SCLC patients developing SIADH 2, 3, 4
- The syndrome is caused by the ectopic secretion of antidiuretic hormone (ADH), leading to hyponatremia and other symptoms 5, 3, 6
- Other factors, such as neurocognitive deficits and volemic status, can contribute to the development and severity of SIADH 2, 5, 4
Clinical Presentation
- Patients with SIADH often present with severe hyponatremia, which can cause significant neurocognitive deficits and other symptoms 2, 5, 6
- The severity of symptoms can vary, but in severe cases, patients may experience generalized seizures and other life-threatening complications 6
- Laboratory tests, such as urine osmolality and urine sodium, can help diagnose SIADH, but treatment may need to be initiated before test results are available 5
Treatment Options
- Tolvaptan, a vasopressin-2 receptor antagonist, has been shown to be effective in treating SIADH, particularly in patients with SCLC 2, 3, 6
- Restriction of fluid intake may also be used to manage SIADH, but this may not be tolerated by all patients 6
- Other treatment options, such as hypertonic saline, may be used in emergency situations or in patients with severe symptoms 5