Syringomyelia associated with inappropriate antidiuretic hormone secretion.

Hyponatraemia is the most common fluid-electrolyte disorder, and the most frequent related aetiologies are syndrome of inappropriate secretion of antidiuretic hormone (SIADH), which accounts for up to 38%. SIADH has been linked to multiple pathologies that affect the central nervous system; these disorders generally originate in the brain and, more rarely, in the spinal cord. It is often observed in patients undergoing neurosurgery and in patients with head injuries or intracranial tumours, and less common in those with spinal pathologies, especially traumatic.