From a recent study:
A single-center retrospective study including all patients diagnosed with SIADH in a large community hospital and tertiary center between 1.1.2007 and 1.1.2013...
The study cohort included 555 patients. The most common etiologies were malignancies and medication-induced SIADH, followed by idiopathic SIADH, pulmonary infections, pain and nausea, and central nervous system (CNS) disorders. Subgroup analysis according to etiology showed that CNS disorders were associated with more severe episodes of SIADH. Patients with idiopathic SIADH were older than patients with a specific diagnosis, had a lower urine osmolality, and required less treatment with hypertonic saline. Long-term survival was determined primarily by SIADH etiology rather than hyponatremia severity, with hazard ratios for death of up to 7.31 (95% CI 4.93–10.82, p less than 0.001) for patients with malignancy-associated SIADH as compared to patients with idiopathic SIADH. Hyponatremia grade at short-term follow-up was also predictive for long-term survival (HR 1.42 per grade, 95% CI 1.21–1.66, p less than 0.001).