Hyponatremia secondary to transient renal salt wasting (TRSW): A not so uncommon observation in the elderly .

Aims: We attempted to classify 115 consecutive nonedematous hyponatremic patients according to their history and saline responsiveness. We hereby describe 6 out of them presenting a transient renal salt wasting (TRSW) state of unknown origin.

Materials And Methods: Six patients with an initial SNa of 126 ± 3 mEq/L were included in the study. They were treated with 2 L isotonic saline infusion over 24 hours. The evolution of the biochemical data of 5 patients were compared to 6 patients with syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH), 6 hyponatremias following the use of thiazides, and to 5 salt-depleted hyponatremic patients of similar age and body weight, treated in the same way.

Results: The mean values of FEurea and FEuric acid in the 6 described patients, together with a clearly inappropriate natriuresis suggested SIADH. However, the high mean fractional potassium excretion (FEK = 34 ± 15%) was not observed in SIADH (13 ± 3%) (p < 0.01). Plasma sodium levels improved quickly after saline infusion in most of these patients, while fractional solute excretions and diuresis decreased. Calciuria is increased in patients with renal salt waisting (RSW), while low calciuria values are observed in the thiazide group. Four of the 6 hyponatremic patients were admitted for syncopal malaise or fall.

Conclusion: We observed in 6 out of 115 consecutive hyponatremic patients a TRSW. RSW as a diagnosis has to be considered when in hyponatremia with excessive natriuresis, high FEK and an intake of diuretics is ruled out. This hyponatremia is saline-responsive, but relapse can be frequently observed.