6520 Stimulated Copeptin Measurement in the Evaluation of a Patient Presenting Hypernatremia and Adipsia

Abstract Disclosure: B.R. Assunção: None. M.M. Freire: None. M. De Castro: None. A.C. Moreira: None. P.C. Elias: None. Introduction: Hypernatremia (hyperNA) in patients submitted to neurosurgery involving the hypothalamic region prompts the diagnosis of vasopressin deficiency (AVP-D), typically accompanied by increased thirst, polydipsia and polyuria. Classic adipsic AVP-D is characterized by hypotonic polyuria and no thirst in response to hyperNA. Clinical Case: A 21 yo male patient, followed since he had a surgery for a pilocytic astrocytoma of the third ventricle at 12 yo, presented hyperNA (154 mEq/L) with mild dehydration. He denied increased thirst, polyuria or polydipsia. Further evaluation showed elevated plasma and urinary osmolalities (pOsm: 317 mOsm/Kg; uOsm: 878 mOsm/Kg). The patient was admitted for hydration and fluid balance. Oral water intake (2500-3000L/day) was prescribed. Serum sodium (Na+) decreased from 158 to 133 mEq/L within 72h, and no polyuria was detected at hyper or normonatremic states. A 3% saline infusion test (SIT) was performed with thirst visual scale and plasma copeptin (CP) assessment. Na+ rose from 139 to 150 mEq/L and pOsm from 295 to 321 mOsm/kg, with no rise in thirst scale (4,2 to 4,8 cm). Basal and maximal 3% SIT CP levels were 3.1 and 3.2 pmol/L, respectively, also displaying subnormal values. CP assessed under hypovolemic hyperNA (Na+: 158 mEq/L) was 4.1 pmol/L, suggesting that this patient might have an adispic disorder with subnormal thirst and AVP osmotic responses, explaining the lack of polyuria. Patient was treated with fixed daily fluid intake with a last follow-up Na+ of 141 mEq/L.Discussion: Adipsic AVP-D is characterized by hypotonic polyuria and no thirst in response to hyperNA. However, polyuria, a hallmark of clinical presentation, was not observed in the present case. Other adipsic disorders include upward resetting of the osmotic thresholds for both thirst and AVP release (Type A); sub-normal thirst and AVP responses to osmotic stimuli (Type B); and intact osmoregulation of AVP release with absent thirst response (Type D). The lack of polyuria even in normovolemic conditions and the subnormal thirst and CP responses to normovolemic hyperNA and dehydrate states suggest the present case to be a Type B adipsic disorder. In those patients, the secretion of small amounts of AVP in response to osmotic stimulation explains why they retain the ability to concentrate urine, limiting free water excretion. Treatment is based on a fixed fluid intake of around 2 liters per day. Conclusions: Adipsic AVP-D and other adipsic disorders are extremely rare, presenting a great challenge in the diagnosis and management. To our knowledge, this is the first description of CP assessment in a patient with hyperNA and adipsia. CP might be an important diagnostic approach to adipsic disorders. Presentation: 6/2/2024