Non-Pharmacological Causes of SIADH

Introduction to SIADH Causes

• SIADH has three major non-pharmacological etiologic categories: malignancies, central nervous system disorders, and pulmonary diseases 1, 2

Malignant Causes

• Small cell lung cancer is the most common malignant cause of SIADH, occurring in approximately 15% of small cell lung cancer patients 2

Central Nervous System Disorders

• CNS pathology represents a major category of SIADH causes, with mechanisms involving disruption of hypothalamic-pituitary function 2
• Subarachnoid hemorrhage is a specific CNS cause of SIADH 1, 2
• A critical clinical pitfall: In neurosurgical patients, you must distinguish SIADH from cerebral salt wasting (CSW), as they require opposite treatments 1

Pulmonary Disorders

• Intrathoracic non-malignant conditions are well-established causes of SIADH through nonosmotic stimulation of AVP release 2
• Pneumonia and other pulmonary infections can cause SIADH 1

Post-Operative State

• Hospital-acquired hyponatremia from hypotonic IV fluids affects 15-30% of hospitalized patients and is entirely preventable by using isotonic maintenance fluids 1

Clinical Context and Reversibility

• For cancer patients with SIADH, 20-50% of delirium episodes can be reversed if the patient is not imminently dying 3
• The optimal therapy for malignancy-related SIADH is treating the underlying cancer, as hyponatremia usually improves after successful treatment of the underlying cause 1