Idiopathic Arginine Vasopressin Deficiency With Mild and Reversible Hypercalcemia

Background: Arginine vasopressin deficiency (central diabetes insipidus) results from impaired hypothalamic-neurohypophyseal secretion of arginine vasopressin and leads to hypotonic polyuria and polydipsia. Common causes of arginine vasopressin deficiency include head trauma, pituitary surgery, neoplasms, and inflammatory stalk lesions; however, 25% to 50% of cases are idiopathic. Hypercalcemia can result in arginine vasopressin resistance (nephrogenic diabetes insipidus) and is an important differential in the evaluation of patients with hypotonic polyuria-polydipsia syndrome. Case Report: A 32-year-old male presented with polyuria (24-hour urine output of 144 mL/kg), polydipsia (24-hour fluid intake of 130 mL/kg), and nocturia of 6 months' duration. Baseline investigations revealed normal liver, renal, serum potassium, and blood glucose levels. After overnight dehydration, serum osmolality increased to 317 mOsm/kg, while urine osmolality remained inappropriately low at 156 mOsm/kg. Mild hypercalcemia (serum calcium of 11.1 mg/dL) was noted. Upon arginine vasopressin challenge, urine osmolality increased by nearly 300%, suggesting complete arginine vasopressin deficiency. Evaluation for secondary causes was unremarkable. Magnetic resonance imaging of the pituitary revealed a normal anterior pituitary and pituitary stalk with an absent posterior pituitary bright spot. Idiopathic arginine vasopressin deficiency was diagnosed. The patient responded to oral desmopressin replacement, and normocalcemia was documented in multiple samples repeated when the patient was in a hydrated state. Conclusion: Patients with arginine vasopressin deficiency can manifest concomitant mild and reversible dehydration-related hypercalcemia. A brisk increase in urine osmolality following subcutaneous arginine vasopressin injection and normal serum calcium levels after desmopressin therapy can establish that hypercalcemia is the effect and not the cause of the primary disorder.