Analysis of water and electrolyte imbalance in a patient with adipsic hypernatremia associated with subfornical organ-targeting antibody.

Patients with adipsic hypernatremia present with chronic hypernatremia because of defects in thirst sensation and dysregulated salt appetite, without demonstrable hypothalamic structural lesions. The involvement of autoantibodies directed against the sodium channel, Nax in the subfornical organ (SFO) has recently been reported. However, the pathophysiology of water and electrolyte imbalance underlying the disease has yet to be elucidated. We describe the case of a 5-year-old boy who complained of headaches and vomiting that gradually worsened. Brain magnetic resonance imaging detected no abnormal lesions. Blood laboratory testing revealed a serum sodium (Na) concentration of 152 mmol/L and a serum osmolarity of 312 mOsm/L. His body weight had slightly decreased, and his thirst sensation was absent. His plasma vasopressin concentration was 0.9 pg/mL, despite the high serum osmolarity. He was encouraged to drink water, and oral 1-deamino-8-D-arginine-vasopressin was administered. When serum sodium concentrations were normalized, plasma vasopressin concentrations were apparently normal and ranged from 0.8 to 2.0 pg/mL. He did not present with polyuria at any time. Immunohistochemical study using mouse brain sections and the patient's serum revealed the deposition of human immunoglobulin G (IgG) antibody in the mouse SFO. In conclusion, our observations suggested that water and electrolyte imbalance in adipsic hypernatremia is characterized by a certain amount of vasopressin release regardless of serum sodium concentrations with no response to hyperosmolarity.