ESPE Abstracts

Introduction: Differential diagnosis of partial central diabetes insipidus (PCDI) and primary polydipsia (PP) is challenging. Copeptin, a stable biomarker derived from the vasopressin precursor peptide, increases in response to arginine infusion. This has been utilized to distinguish between central diabetes insipidus (CDI) and PP, with a cutoff of 3.8 pmol/L at 60' post-infusion in adults.

Objective: Evaluate arginine-copeptin test efficacy and safety in paediatric patients.

Patients and Methods: Descriptive and prospective study on diagnosing paediatric patients with polydipsia-polyuria syndrome. Inclusion criteria: <18 years, polyuria (>2mL/kg/h), normal blood glucose and no electrolytes imbalances. Arginine-copeptin test: 0.5g/kg of intravenous arginine with analytical and vital signs monitoring (Times: baseline,0',30',60',90',120').

Results: Eleven patients, all remaining asymptomatic and hemodynamically stable throughout the procedure. No biochemical abnormalities observed. Four patients, with copeptin levels <3.8pmol/L at 60' were diagnosed with CDI, responding well to desmopressin:

Patient 1: 5-year-old boy with sudden-onset polyuria. MRI: hypoplastic adenohypophysis, absent neurohypophysis signal and normal pituitary stalk. After 15-hour water restriction, maximum urinary osmolality (Osmu): 601 mOsm/kg, increasing to 845 mOsm/kg (post-desmopressin). Arginine-copeptin test (60’: 2.3 pmol/L). Diagnosis: PCDI. Negative tumor markers. Normal AVP gene, pending complete genetic study.

Patient 3: 13-year-old boy with sudden-onset polyuria. Baseline: plasma osmolality of 303 mOsm/kg and Osmu of 98 mOsm/kg, therefore the water deprivation test was not conducted. Osmu increased to 507 mOsm/kg post-desmopressin. Arginine-copeptin test (60’: 1.78 pmol/L). Diagnosis: CDI. MRI: absent neurohypophysis signal and pituitary stalk thickening, which resolved spontaneously. Negative cerebrospinal fluid tumor markers. Suspected diagnosis: lymphocytic hypophysitis.

Patient 9: 9-year-old girl with high-grade thalamopeduncular glioma diagnosed due to short stature. MRI: lesion with third ventricle collapse and hydrocephalus (normal adenohipofisis and neurohipofisis). Arginine-copeptin test (60’: 3.4 pmol/L). Diagnosis: Probable CDI.

Patient 10: 6-year-old girl with sudden-onset polyuria and MRI: absent neurohypophysis signal, normal pituitary stalk and adenohypophysis. Arginine-copeptin (60’: 3.1 pmol/L). Diagnosis: CDI. Negative blood tumor markers, AVP gene study pending.

Conclusion: The arginine-copeptin test is a simple and safe method that may serve as an alternative for diagnosing central diabetes insipidus in paediatric patients.