Which condition is associated with euvolemic hypotonic hyponatremia?

Euvolemic hypotonic hyponatremia is commonly associated with conditions that lead to an excess of water relative to sodium in the body, without significant volume depletion or expansion. Primary polydipsia and the syndrome of inappropriate antidiuretic hormone secretion (SIADH) are classic examples of such conditions.

In primary polydipsia, excessive water intake overwhelms the kidney's ability to excrete water, leading to dilution of serum sodium levels. This occurs despite normal overall body fluid volume, hence the term "euvolemic." Similarly, in SIADH, there is an inappropriate release of antidiuretic hormone (ADH). This hormone promotes water reabsorption in the kidneys, resulting in concentrated urine and diluted blood sodium levels, all while maintaining a normal intravascular volume.

These conditions contrast with others like bacterial infections or kidney failure, which may be associated with changes in fluid status (either loss or retention) and can lead to different forms of hyponatremia. In chronic kidney disease, for instance, patients often face disturbances in sodium and water handling leading to different clinical scenarios.