Arginine or Hypertonic Saline-Stimulated Copeptin to Diagnose AVP Deficiency

Hypopituitarism

Partial or complete deficiency of anterior or posterior pituitary hormone production leads to central hypoadrenalism, central hypothyroidism, hypogonadotropic hypogonadism, growth hormone deficiency, or arginine vasopressin deficiency depending on the hormones affected. Hypopituitarism is rare and likely to be underdiagnosed, with an unknown but rising incidence and prevalence. The most common cause is compressive growth or ablation of a pituitary or hypothalamic mass. Less common causes include genetic mutations, hypophysitis (especially in the context of cancer immunotherapy), infiltrative and infectious disease, and traumatic brain injury. Clinical features vary with timing of onset, cause, and number of pituitary axes disrupted. Diagnosis requires measurement of basal circulating hormone concentrations and confirmatory hormone stimulation testing as needed. Treatment is aimed at replacement of deficient hormones. Increased mortality might persist despite treatment, particularly in younger patients, females, and those with arginine vasopressin deficiency. Patients with complex diagnoses, pregnant patients, and adolescent pituitary-deficient patients transitioning to adulthood should ideally be managed at a pituitary tumour centre of excellence.

Evaluation of copeptin in children after stimulation with clonidine or L-Dopa

OBJECTIVES

Arginine-stimulated serum copeptin has been proposed as a new method to diagnose arginine vasopressin (AVP) deficiency in children and adolescents. Herein we investigated the secretagogic potential of clonidine or L-Dopa on the copeptin serum levels in children.

METHODS

Eight stimulation tests (4 with clonidine and 4 with L-Dopa) were performed in eight children (5 boys and 3 girls) with a median age of 6.5 years-old, evaluated for short stature due to possible growth hormone deficiency. Serum copeptin levels were measured at 30, 60, 90, and 120 min after administration of clonidine or L-Dopa.

RESULTS

Copeptin levels in serum did not show any significant change in either test (clonidine or L-Dopa). The values of copeptin levels compared to the baseline value did not deviate more than 5 % in the clonidine arm (p=0.60) or 8 % in the L-Dopa arm (p=0.75) respectively.

CONCLUSIONS

Data do not support the use of L-Dopa or clonidine as stimulants for evaluating AVP relating disorders in clinical pediatric practice.

Apelin and Copeptin Levels in Patients With Chronic SIAD Treated With Empagliflozin

Background

Empagliflozin increases sodium levels in patients with a chronic syndrome of inappropriate antidiuresis (SIAD), and dapagliflozin increases apelin levels in patients with diabetes mellitus. Exogenous apelin increases sodium levels in rats with SIAD. We aimed to investigate whether an increase in plasma apelin concentration may contribute to the efficacy of empagliflozin in SIAD.

Methods

Post hoc secondary analysis of a double-blind, crossover, placebo-controlled trial performed from December 2017 to August 2021 at the University Hospital Basel, Switzerland, investigating the effect of 4-week treatment with empagliflozin 25 mg/day as compared to placebo in 14 outpatients with chronic SIAD (NCT03202667). The objective was to investigate the effect of empagliflozin on plasma apelin and copeptin concentrations and their ratio.

Results

Fourteen patients, 50% female, with a median [interquartile range] age of 72 years [65-77] were analyzed. Median apelin concentration was 956 pmol/L [853, 1038] at baseline. Median [interquartile range] apelin relative changes were +11% [0.7, 21] and +8% [-5, 25] (P = .672) at the end of the placebo and empagliflozin phases, respectively. Median copeptin concentration was 2.6 [2.2, 4.5] pmol/L at baseline and had a relative change of +5 [-2. 11]% and +25% [10, 28] (P = .047) over the placebo and empagliflozin phases, respectively.

Conclusion

Empagliflozin did not lead to significant changes in apelin or the apelin/copeptin ratio in patients with chronic SIAD but led to an increase in copeptin. This suggests that the efficacy of empagliflozin in SIAD is independent of apelin and is not blunted by the adaptative increase in copeptin.

Copeptin Stimulation by Combined Intravenous Arginine and Oral LevoDopa/Carbidopa in Healthy Short Children and Children with the Polyuria-Polydipsia Syndrome

INTRODUCTION

Stimulated copeptin may provide an alternative to water deprivation testing (WDT) in the evaluation of polyuria-polydipsia syndrome (PPS). Though best studied, arginine stimulation alone produces a modest copeptin response in children. We investigated the effectiveness of the arginine + LevoDopa/Carbidopa stimulation test (ALD-ST) for copeptin.

METHODS

47 healthy short children (controls), 10 children with primary polydipsia, and 10 children with AVP deficiency received arginine hydrochloride (500 mg/kg intravenously over 30 min) and Levodopa/carbidopa (10:1 ratio; 175 mg of l-Dopa/m2 BSA) orally. Serum copeptin was measured at 0, 60, 90, and 120 min.

RESULTS

In controls, ALD-ST increased copeptin from a median of 7.0 pmol/L (IQR 5.0-10.0) to a peak of 44.0 pmol/L (IQR 21.4-181.0) between 60 and 120 min (p < 0.001). Copeptin peak was higher in subjects who experienced nausea or vomiting (57%) than in those who did not (131.0 pmol/L [IQR 42.5-193.8] vs. 22.7 pmol/L [IQR 16.0-33.7], p < 0.001). While subjects with primary polydipsia had similar baseline (8.5 pmol/L [IQR 8.0-11.0]) and stimulated (125.2 pmol/L [IQR 87.6-174.0]) copeptin levels as controls, subjects with AVP deficiency had lower baseline (2.5 pmol/L [IQR 2.0-3.1]) and peak levels (4.6 pmol/L [IQR 2.4-6.0]). A peak copeptin of ≥9.3 pmol/L best predicted absence of complete or partial AVP deficiency with a sensitivity of 100% and specificity of 80%.

CONCLUSIONS

ALD-ST induced a robust peak copeptin in healthy short children and children with primary polydipsia. Nausea/vomiting, a side effect of ALD-ST, amplified the copeptin response. The ALD-ST may be a suitable initial screening test in children with PPS.

Psychopathological characteristics in patients with arginine vasopressin deficiency (central diabetes insipidus) and primary polydipsia compared to healthy controls

OBJECTIVE

Distinguishing arginine vasopressin deficiency (AVP-D; central diabetes insipidus) from primary polydipsia (PP), commonly referred to as psychogenic polydipsia, is challenging. Psychopathologic findings, commonly used for PP diagnosis in clinical practice, are rarely evaluated in AVP-D patients, and no comparative data between the two conditions currently exist.

DESIGN

Data from two studies involving 82 participants [39 AVP-D, 28 PP, and 15 healthy controls (HC)].

METHODS

Psychological evaluations were conducted using standardized questionnaires measuring anxiety [State-Trait Anxiety Inventory (STAI)], alexithymia [Toronto Alexithymia Scale (TAS-20)], depressive symptoms (Beck's Depression Inventory-II (BDI-II), and overall mental health [Short Form-36 Health Survey (SF-36)]. Higher STAI, TAS-20, and BDI-II scores suggest elevated anxiety, alexithymia, and depression, while higher SF-36 scores signify better overall mental health.

RESULTS

Compared to HC, patients with AVP-D and PP showed higher levels of anxiety (HC 28 points [24-31] vs AVP-D 36 points [31-45]; vs PP 38 points [33-46], P < .01), alexithymia (HC 30 points [29-37] vs AVP-D 43 points [35-54]; vs PP 46 points [37-55], P < .01), and depression (HC 1 point [0-2] vs AVP-D 7 points [4-14]; vs PP 7 points [3-13], P < .01). Levels of anxiety, alexithymia, and depression showed no difference between both patient groups (P = .58, P = .90, P = .50, respectively). Compared to HC, patients with AVP-D and PP reported similarly reduced self-reported overall mental health scores (HC 84 [68-88] vs AVP-D 60 [52-80], P = .05; vs PP 60 [47-74], P < .01).

CONCLUSION

This study reveals heightened anxiety, alexithymia, depression, and diminished overall mental health in patients with AVP-D and PP. The results emphasize the need for careful interpretation of psychopathological characteristics to differentiate between AVP-D and PP.

Arginine vasopressin deficiency: diagnosis, management and the relevance of oxytocin deficiency

Polyuria-polydipsia syndrome can be caused by central diabetes insipidus, nephrogenic diabetes insipidus or primary polydipsia. To avoid confusion with diabetes mellitus, the name 'central diabetes insipidus' was changed in 2022 to arginine vasopressin (AVP) deficiency and 'nephrogenic diabetes insipidus' was renamed as AVP resistance. To differentiate the three entities, various osmotic and non-osmotic copeptin-based stimulation tests have been introduced in the past decade. The hypertonic saline test plus plasma copeptin measurement emerged as the test with highest diagnostic accuracy, replacing the water deprivation test as the gold standard in differential diagnosis of the polyuria-polydipsia syndrome. The mainstay of treatment for AVP deficiency is AVP replacement with desmopressin, a synthetic analogue of AVP specific for AVP receptor 2 (AVPR2), which usually leads to rapid improvements in polyuria and polydipsia. The main adverse effect of desmopressin is dilutional hyponatraemia, which can be reduced by regularly performing the so-called desmopressin escape method. Evidence from the past few years suggests an additional oxytocin deficiency in patients with AVP deficiency. This potential deficiency should be further evaluated in future studies, including feasible provocation tests for clinical practice and interventional trials with oxytocin substitution.

The diagnostic role of arginine-stimulated copeptin in the differential diagnosis of polyuria-polydipsia syndrome (PPS) in pediatric age

PURPOSE

In recent years, copeptin stimulation through arginine administration has been evaluated as a new potential tool in the differential diagnosis of polyuria-polydipsia syndrome (PPS) in adults; to date very few data, all retrospective, exist in pediatric age. The aim of this prospective study is to evaluate the diagnostic performance of the arginine-stimulation test for copeptin in a cohort of pediatric patients affected by PPS.

METHODS

All children (<18 years) referred to the Department of Pediatric Endocrinology of the Regina Margherita Children Hospital for polyuria-polydipsia in the period January 2021-June 2023 were enrolled. The Arginine-stimulation test for copeptin was performed in all patients presenting PPS after water deprivation test (WDT). Patients with polyuria-polydipsia were then classified as having primary polyuria (PP), complete and partial central diabetes insipidus (CDI), according to the standardized interpretation. Arginine-stimulation test for copeptin was also performed in a control cohort.

RESULTS

A significant difference in arginine-stimulated copeptin values was observed at baseline (p = 0.005), at 60 min (p = 0.01), and at 90 min (p = 0.005) in 7 subjects presenting PP, 6 patients affected by CDI and 50 subjects of the control cohort. Plasma osmolality values remained stable at all measurements. The arginine-stimulated copeptin test demonstrated sensitivity and specificity of 100%, whereas the sensitivity of the WDT test was 83.3% and the specificity was 85.7%.

CONCLUSION

Given the reliability and the minor adverse effects and costs, the copeptin level after arginine administration could replace the WDT in the diagnostic workup of these in pediatric age.

Diabetes insipidus: Vasopressin deficiency…

Diabetes insipidus is a disorder characterized by hypo-osmotic polyuria secondary to abnormal synthesis, regulation, or renal action of antidiuretic hormone. Recently, an expert group, with the support of patient associations, proposed that diabetes insipidus be renamed to avoid confusion with diabetes mellitus. The most common form of diabetes insipidus is secondary to a dysfunction of the neurohypophysis (central diabetes insipidus) and would be therefore named â€̃vasopressin deficiency’. The rarer form, which is linked to renal vasopressin resistance (nephrogenic diabetes insipidus), would then be named â€̃vasopressin resistance’. The etiology of diabetes insipidus is sometimes clear, in the case of a neurohypophyseal cause (tumoral or infiltrative damage) or a renal origin, but in some cases diabetes insipidus can be difficult to distinguish from primary polydipsia, which is characterized by consumption of excessive quantities of water without any abnormality in regulation or action of antidiuretic hormone. Apart from patients’ medical history, physical examination, and imaging of the hypothalamic-pituitary region, functional tests such as water deprivation or stimulation of copeptin by hyperosmolarity (induced by infusion of hypertonic saline) can be proposed in order to distinguish between these different etiologies. The treatment of diabetes insipidus depends on the underlying etiology, and in the case of a central etiology, is based on the administration of desmopressin which improves patient symptoms but does not always result in an optimal quality of life. The cause of this altered quality of life may be oxytocin deficiency, oxytocin being also secreted from the neurohypophysis, though this has not been fully established. The possibility of a new test using stimulation of oxytocin to identify alterations in oxytocin synthesis is of interest and would allow confirmation of a deficiency in those patients presenting with diabetes insipidus linked to neurohypophyseal dysfunction.

Paediatric perspectives in the diagnosis of polyuria-polydipsia syndrome

The elucidation of the underlying cause of polyuria-polydipsia syndrome (PPS) is a challenging-especially in the differentiation of partial defects of arginine vasopressin (AVP) secretion or action from primary polydipsia. The water deprivation test has been utilized for many decades, and its application in the paediatric population has been applied using parameters predominantly established in adult cohorts. In more recent times, the development of automated commercial assays for copeptin, a surrogate marker for AVP, has represented a significant advancement in the diagnostic approach to PPS. Measurement of copeptin concentrations has major advantages and has essentially superseded measurement of AVP in diagnostic protocols for PPS. Additionally, stimulated-copeptin protocols utilizing hypertonic saline infusion, arginine, and glucagon have been investigated, and are promising. However, further studies are required in the population-incorporating the differences in physiological regulation of water homeostasis, and safety requirements-before there is widespread adoption into clinical practice.