AVP and inappropriate ADH syndrome: These two theories for hyponatremia, SIADH and CSWS, are contradictory as follows: SIADH is hypervolemic hyponatremia that is caused by water retention, while CSWS is hypovolemic hyponatremia that is caused by excessive sodium excretion; SIADH is the hypersecretion of antidiuretic hormone which also known as arginine vasopressin (AVP), while CSWS is the hyposecretion of AVP; and SIADH requires water restriction and CSWS requires fluid replacement therapeutically.