OBJECTIVES: Essential hypernatremia is very rare in clinical practice and the pathogenesis is unclear. We performed a set of clinical tests to a patient with chronic and sustained hypernatremia as well as absence of thirst in order to investigate the clinical characteristics and make the diagnosis, yet most importantly to analyze the possible pathogenesis and explore a possible therapy regime.
METHODS: Water deprivation test and acute water intravenous loading test were performed to observe the changes of urinary osmolality, plasma osmolality and plasma sodium. Free water clearance (C(H₂O) was calculated. Osmolality was detected using the method of freezing point depression, and thirst grade using visual analogue scales. Desmopressin acetate (0.05-0.1 mg/d) was administered to the patient in order to observe the therapeutic effects to his disorder.
RESULTS: The patient had sustained hypernatremia over a long period of time, decreased thirst, normal renal function, as well as absence of clinical hypovoluemia. The plasma sodium was 160-190 mmol/L and plasma osmolality was 330-370 mOsm/L without any thirst perception which could not be corrected by water intake. An 18-hour period of water deprivation increased the urinary osmolality from 368 mOsm/L to 420 mOsm/L with plasma osmolality increasing from 362 mOsm/L to 369 mOsm/L and rising further to 857 mOsm/L after an injection of 5 u vasopresin. With the infusion of 1 250 ml 5%-glucose during 2 hours in an acute water loading test setting, plasma osmolality decreased from 350 mOsm/L to 334 mOsm/L associated with a plasma sodium decrease from 164.7 mmol/L to 155 mmol/L urinary osmolality dropped from a maximum of 632 mOsm/L to 135 mOsm/L urinary volume from 0.25 ml/min to 2.33 ml/min and C(H₂O) from -0.18 ml/min to 1.19 ml/min after acute water loading with 1 250 ml glucose dissolved in water. Our results reveal that treatment of the patient with Desmopressin acetate relieved the adypsia, hypernatremia and hyperosmolality effectively.
CONCLUSIONS: The patient was considered as suffering from essential hypernatremia which was associated with partial central diabetes insipidus and adypsia. Desmopressin acetate as a common therapeutic agent of central diabetes insipidus proved to be an effective treatment for essential hypernatremia.