Euvolemic hyponatremia in cancer patients. Report of the Hyponatremia Registry: an observational multicenter international study

Purpose: Hyponatremia secondary to SIADH is frequent in cancer patients and potentially deleterious. The aim of this sub-analysis of the Hyponatremia Registry database is to analyze current diagnostic and therapeutic management practices in cancer patients with SIADH.

Methods: We analyzed 358 cancer patients who had serum sodium concentration ([Na⁺]) ≤ 130 mEq/L and a clinical diagnosis of SIADH from 225 sites in the USA and EU.

Results: Precise diagnostic testing was performed in only 46%. Almost 12% of all patients did not receive any hyponatremia treatment. The most frequent therapies were fluid restriction (20%), isotonic saline (14%), fluid restriction/isotonic saline (7%), tolvaptan (8%), and salt tablets (7%). Hypertonic saline was used in less than 3%. Tolvaptan produced the greatest median rate of [Na⁺] change (IQR) (3.0 (4.7) mEq/L/day), followed by hypertonic saline (2.0(7.0) mEq/L/day), and fluid restriction/isotonic saline (1.9(3.2) mEq/L/day). Both fluid restriction and isotonic saline monotherapies were significantly less effective (0.8(2.0) mEq/L/day and 1.3(3.0) mEq/L/day, respectively) and were associated with clinically relevant rates of treatment failure. Only 46% of patients were discharged with [Na⁺] ≥ 130 mEq/L. Overly rapid correction of hyponatremia occurred in 11.7%.

Conclusions: Although essential for successful hyponatremia management, appropriate diagnostic testing is not routinely performed in current practice. The most frequently employed monotherapies were often ineffective and sometimes even aggravated hyponatremia. Tolvaptan was used less often but showed significantly greater effectiveness. Despite clear evidence that hyponatremia is associated with poor outcome in oncology patients, most patients were discharged still hyponatremic. Further studies are needed to assess the beneficial impact of hyponatremia correction with effective therapies.