We are the witnesses of a significant increase in chronic kidney diseases (CKD) occurrence. There is scarce literature evidence about functional integrity and natural adaptation of endocrine system axes in patients with different stages of always progressive CKD. Such a problem is growing with the beginning of renal replacement treatments (peritoneal and hemodialysis) or even with renal transplantation. The close monitoring of CKD patients by nephrologist and endocrinologist is mandatory because the natural adaptation of the endocrine system in CKD patients must be differed out of endocrine dysfunction, which has to be treated. Endocrine dysfunction management principles are mostly the same as for the patients with no CKD, except for close drug dose monitoring, especially in the circumstances with concomitant renal replacement treatment.

Hyponatremia is an electrolyte disorder frequently encountered in clinical practice. The first step in the diagnostic evaluation of hyponatremia is the volume assessment (clinical estimation of hypo/hypervolemia presence). In the cases of euvolemic hyponatremia, followed by decreased plasma osmolality (<275mOsm/kg) with urine osmolality >100mOsm/kg, urine sodium >30mmol/L along with normal intake of salt and water, preserved pituitary, adrenal, thyroid, adrenal function as well as no recent use of diuretics, syndrome of inappropriate diuresis (SIAD) is diagnosed. In symptomatic, especially acute hyponatremia, careful and gradual substitution by 3 (10) % sodium-chloride infusion is advised with liquid intake restriction, the administration of demeclocycline, urea, or vaptans, as well as causal treatment of SIAD. SIAD is often transient and etiologically clear. In this paper, we present two cases with idiopathic, chronic SIAD with poor outcomes. During the diagnostic follow-up, the cause of SIAD was not found. The autopsy finding was also adverse. In most cases, euvolemic hyponatremia in patients with chronic, idiopathic SIAD is an ominous sign.