ESPE Abstracts

Introduction: Differential diagnosis of partial central diabetes insipidus (PCDI) and primary polydipsia (PP) can be challenging. Copeptin is the C-terminal segment of the vasopressin precursor peptide that represents a novel and stable biomarker. Arginine infusion produces a nonosmotic stimulus that causes an increase in copeptin concentrations in healthy subjects. Arginine-stimulated copeptin concentrations have been used to differentiate between patients with central diabetes insipidus (CDI) and PP, setting a copeptin value of 3.8 pmol/l at 60 min as a cut-off point in adults.

Objective: To evaluate the efficacy and safety of the arginine-stimulated test in paediatrics.

Patients and methods: Three patients with polydipsia-polyuria syndrome. After water restriction/desmopressin test, arginine-stimulated test was accomplished. Time points: basal 0',30',60',90',120'. To verify the safety of the test, vital signs and blood tests were monitored.

Results:

Patient 1: 5-year-old boy with sudden polydipsia-polyuria syndrome. The 15-hour water restriction test resulted in a maximum urinary osmolality (Osmu) of 601 mOsm/kg that increased up to 845 mOsm/kg after desmopressin. Arginine-copeptin test showed a flat curve with a low copeptin at 60'. Polydipsia-polyuria syndrome clearly improved on desmopressin treatment. MRI showed a small and hypoplastic adenohypophysis with absense of the neurohypophysis signal.

Patient 2: 12-year-old boy with syntelencephaly and severe optochiasmatic atrophy, dysgenetic corpus callosum, without alterations in the hypothalamic-pituitary region. He presented a long-standing polydipsia-polyuria syndrome. The 17-hour water restriction test resulted in a maximum Osmu of 495 mOsm/kg that increased up to 687 mOsm/kg after desmopressin. Arginine-copeptin test showed a flat response but with values above the cut-off point. Desmopressin was started without improvement, therefore it was suspended. Polydipsia-polyuria syndrome improved spontaneously afterwards.

Patient 3: 13-year-old boy with sudden polydipsia-polyuria syndrome. In the basal analysis, he presented plasma osmolality of 303 mOsm/Kgm and water restriction was not performed. Osmu of 98 mOsm/kg increased up to 507 mOsm/kg with desmopressin. Arginine-copeptin test showed a flat curve with low copeptin at 60'. MRI showed an absence of the neurohypophysis and thickening of the pituitary stalk, etiological study pending.

Conclusion: The arginine-stimulated copeptin test is a safe procedure and can represent an alternative to the diagnosis of CDI.