AQP4 and Hyponatremia: Among the areas with high AQP-4 expression, the area postrema, a chemo-sensitive vomiting center, can be the first attack point of NMOSD.[8] attacks on AQP-4 in the paraventricular nucleus regions of the hypothalamus are susceptible to complement-induced damage.[3,9] Some lesions in this area are associated with endocrinopathy, which can lead to SIADH, a condition characterized by dysregulation of antidiuretic hormones.[3,9] SIADH is the most common cause of hyponatremia.[10] Meanwhile, SIADH is needs to be differentiated from CSWS.