The syndrome of abnormal secretion of antidiuretic hormone (SIADH) was first reported by Schwartz in 1957, and is caused by excessive secretion of antidiuretic hormone (ADH, i.e. AVP) or similar antidiuretic hormone-like substances, resulting in impaired water excretion, with hyponatremia as the prominent manifestation. So what are the causes of increased ADH secretion? The abnormal secretion of adrenocorticotropic hormone (ACTH) and antidiuretic hormone (ADH) caused by damage to the subthalamic-pituitary system leads to increased urinary sodium excretion and increased water reabsorption by the kidneys, resulting in a series of clinical symptoms of neurological impairment caused by decreased blood sodium and low blood osmolality, which is called the syndrome of abnormal secretion of antidiuretic hormone, or SIADH for short. In SIADH, there may be no hypovolemia , no hypotension, no non-osmotic stimuli such as adrenal insufficiency, inappropriate elevation of plasma ADH relative to plasma osmolality, and failure to effectively suppress ADH secretion even when plasma osmolality falls below the threshold, while ACTH is relatively under-secreted. It is currently believed that: clinical syndrome caused by abnormal increase in secretion of antidiuretic hormone (ADH) or other similar substances from different sources or their enhanced activity. The main manifestations are water retention in the kidneys, dilutional hyponatremia and increased urinary sodium excretion.