EJE AWARD 2019: New diagnostic approaches for patients with polyuria polydipsia syndrome

Combined Arginine and Insulin Stimulation Elicits a Robust and Consistent Copeptin Response in Short Children

INTRODUCTION

Copeptin, co-secreted with arginine vasopressin, is regulated by osmotic and volume stimuli but also responds to intravenous arginine and insulin-induced hypoglycemia. The serum copeptin response to the latter agents has been studied in adults but only to a limited extent in children. The objective of this study was to describe the copeptin response to combined arginine and insulin in children with normal posterior pituitary function.

METHODS

We conducted a prospective, single-arm assessment of serum copeptin concentrations in children (age 7-16 years, n = 38) undergoing growth hormone stimulation testing with an arginine-insulin tolerance test (AITT) for short stature or growth deceleration in a tertiary referral center. After overnight fasting, arginine (500 mg/kg) was administered between 0 and 30 min intravenously (IV) followed by insulin (0.1 units/kg IV) at 60 min. Copeptin serum concentrations were measured at baseline (0 min), at the post-arginine peak (60 min), and at the post-insulin peak (90 min; 30 min post-insulin), respectively. The main outcome was the peak copeptin concentration.

RESULTS

Mean ± SD copeptin concentrations increased from 9.9 ± 5.0 pmol/L at 0 min to 13.2 ± 5.8 pmol/L at 60 min (p < 0.0001 vs. 0 min) and 27.7 ± 14.2 pmol/L at 90 min (p < 0.0001 vs. 0 and 60 min). There was no significant correlation between copeptin concentrations and age, BMI, pubertal status, cortisol, growth hormone, or glucose concentrations.

DISCUSSION/CONCLUSION

Arginine and insulin appear to have an additive and consistent effect resulting in significant stimulation of copeptin secretion in children. The AITT may be a useful tool to evaluate for normal posterior pituitary function in this age-group, with potential implications for the evaluation of polyuria-polydipsia syndrome.

Everything in excess is opposed to nature, even vitamin D: a case report

SUMMARY

Vitamin D intoxication in children is rare but its incidence is increasing as vitamin D is supplemented more often and in higher doses. Children with cystic fibrosis (CF) are at risk for vitamin D intoxication due to incorrect compounded preparations of liposoluble vitamins. Here, we report a severe vitamin D intoxication in a 4-year-old girl with CF, due to an error in the compounded vitamin A, D, E, and K preparation, presenting clinically with weight loss, constipation, polydipsia, polyuria, and nycturia. The administered compounded preparation contained 10 000-fold the prescribed vitamin D dose. The patient was treated with hyperhydration, loop diuretics, and bisphosphonates. Serum calcium levels normalized after 4 days but serum 25-hydroxyvitamin D levels remained elevated even up to 2 months after treatment.

LEARNING POINTS

Vitamin D intoxication should be ruled out when patients with cystic fibrosis (CF) present with acute polyuria, constipation, and weight loss. Prompt treatment is necessary to avert life-threatening complications. Regularly measuring serum calcium and 25-hydroxyvitamin D concentrations in children with CF receiving vitamin A, D, E, and K supplements is important during their follow-up.

Role of copeptin in the diagnosis of traumatic neuroendocrine dysfunction

Traumatic neuroendocrine dysfunction may present with diabetes insipidus (DI) or with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Both these pathologies involve a disturbance in the antidiuretic hormone (ADH) secretion, causing dysnatremias. Diagnosis of posttraumatic ADH dysfunction is hampered by technical difficulties in ADH assessment, and relies mostly on non-specific serum sodium, serum and urine osmolality and diuresis, often leading to misdiagnosis in the acute care setting. Research now focuses on the diagnostic role of copeptin, a peptide secreted together with ADH in an equimolar fashion, and which can be accurately evaluated. Recent studies identified cut-off values of 2.6 pmol/L for baseline copeptin and of 4.9 and 3.8 pmol/L for hypertonic saline infusion and arginine infusion stimulated copeptin, respectively, for the diagnosis of DI in patients with polyuria-polydipsia syndrome. Although SIADH is more difficult to be explored due to its heterogeneity, a ratio of copeptin to urinary sodium below 30 pmol/mmol identifies euvolemic hyponatremia. Exploring the role of copeptin assessment in patients with traumatic brain injury (TBI) in the acute phase may improve their diagnosis accuracy, management and outcome.

Development of a sensitive liquid chromatography-tandem mass spectrometry method for quantification of human plasma arginine vasopressin

BACKGROUND AND AIMS

Direct measurement of arginine vasopressin (AVP) via immunoassays is not widely conducted, mainly because of technical constraints. Liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been widely used as the gold standard in clinical chemistry. Here, we aimed to develop an MS-based assay to determine human plasma AVP and compare the results with those obtained using a conventional immunoassay.

MATERIALS AND METHODS

We developed a protocol using triple quadrupole MS coupled with LC for the measurement of human plasma AVP. Analytical evaluations of the method were performed, and the results obtained using LC/MS/MS and radioimmunoassay (RIA) were compared.

RESULTS

The lower limit of quantification (LLOQ) for plasma AVP obtained using LC/MS/MS and RIA were 0.2 and 0.4 pg/mL, respectively. Although there was a weak overall correlation between the results obtained using the two different methods, the RIA results did not agree with the LC/MS/MS results, particularly at low concentrations.

CONCLUSIONS

AVP detection through RIA is not satisfactory compared with that using LC/MS/MS. Diagnostic values of direct AVP measurements must be evaluated based on the results obtained via sensitive and accurate MS-based methods rather than those obtained through RIA.

Psychogenic polydipsia in a female adolescent without a psychiatric background: A case report

Psychological stress is a risk factor for primary polydipsia in adolescents without psychiatric comorbidity. Taking a detailed family and social history can help to distinguish primary polydipsia from diabetes insipidus in adolescents with challenging presentations of polydipsia and polyuria.

Lithium, an old friend and a forgotten enemy

INTRODUCTION

Nephrogenic diabetes insipidus (DI) is a polyuric and polydipsic syndrome and can have multiple causing factors.

CASE DESCRIPTION

A 69-year-old woman with bipolar disorder medicated with lithium 400mg for 12 years on a daily basis. The patient was admitted, after psychiatric decompensation, with hypernatremia unresponsive to hypotonic iv fluids. The diagnosis of DI was made with high plasmatic osmolality measurement, low urine osmolality, and high levels of antidiuretic hormone. Full clinical recovery was possible with lithium suspension, hydration, and chlorthalidone.

DISCUSSION

Although frequently used in the past, Lithium (Li) is nowadays rarely used in clinical practice for prolonged treatments because of its potentially devastating side effects. Clinicians must be aware of those side effects in order to prevent organ damage, mainly in patients with severe bipolar disease and precarious response to alternative treatments.

Gestational diabetes insipidus: Diagnosis and management

In the pregnant patient, hypotonic polyuria in the setting of elevated serum osmolality and polydipsia should narrow the differential to causes related to diabetes insipidus (DI). Gestational DI, also called transient DI of pregnancy, is a distinct entity, unique from central DI or nephrogenic DI which may both become exacerbated during pregnancy. These three different processes relate to vasopressin, where increased metabolism, decreased production or altered renal sensitivity to this neuropeptide should be considered. Gestational DI involves progressively rising levels of placental vasopressinase throughout pregnancy, resulting in decreased endogenous vasopressin and resulting hypotonic polyuria worsening through the pregnancy. Gestational DI should be distinguished from central and nephrogenic DI that may be seen during pregnancy through use of clinical history, urine and serum osmolality measurements, response to desmopressin and potentially, the newer, emerging copeptin measurement. This review focuses on a brief overview of osmoregulatory and vasopressin physiology in pregnancy and how this relates to the clinical presentation, pathophysiology, diagnosis and management of gestational DI, with comparisons to the other forms of DI during pregnancy. Differentiating the subtypes of DI during pregnancy is critical in order to provide optimal management of DI in pregnancy and avoid dehydration and hypernatremia in this vulnerable population.