“Clinical and biochemical distinctions between organic and idiopathic arginine vasopressin deficiency (AVP-D) in children”

Purpose: Arginine Vasopressin Deficiency (AVP-D) is a heterogeneous disorder in childhood, characterized by variable clinical severity and a wide range of underlying etiologies. Early identification of organic forms is crucial, as they are frequently associated with structural hypothalamic–pituitary disease and additional endocrine deficits. Methods: We retrospectively analyzed 105 children diagnosed with AVP-D over a 25-yearperiod. Clinical features, etiology, baseline biochemical parameters, and results of dynamictesting were collected. Diagnostic evaluation included the water deprivation test and/orarginine-stimulated copeptin assessment. Copeptin concentrations were measured at baselineand after stimulation. Results: Of the 105 patients (53 males; mean age 7.9 ± 0.5 years), 67 (63.8%) had an organic etiology and 38 (36.2%) an idiopathic form. Children with idiopathic AVP-D were significantly younger at diagnosis (6.3 ± 0.8 vs 8.8 ± 0.6 years; p = 0.01). Organic AVP-D was most commonly caused by craniopharyngioma, germ cell tumors, and congenital hypopituitarism. Associated anterior pituitary hormone deficiencies were present in 92.5% of organic cases versus 23.7% of idiopathic cases (p < 0.0001). Patients with organic AVP-D exhibited significantly higher serum sodium and plasma osmolality at diagnosis, together with markedly lower baseline and stimulated copeptin levels. Diagnosis based solely on baseline biochemical parameters was achieved in 70% of organic cases, compared with 15.8% of idiopathic cases (p< 0.0001). Conclusion: Organic AVP-D in children is characterized by a distinct and more severe biochemical phenotype, with profound copeptin suppression and frequent anterior pituitary involvement. Baseline biochemical assessment, complemented by stimulated copeptin testing when needed, allows accurate etiological stratification and supports a tailored diagnostic approach in pediatric AVP-D.