[A case of cerebral salt wasting syndrome caused by minor head injury].

An 80-year-old woman who was hospitalized due to small subarachnoid hemorrhaging caused by a bruise in the left temporal region of the brain. Nausea/vomiting and malaise appeared after dinner on the fourth day of the illness. Head computed tomography showed that the post-traumatic status was almost normal; however, the sodium ion (Na+) level was 114 mEq/L, indicating severe hyponatremia. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) following a head injury was initially suspected, and water restriction and saline fluid replacement were initiated. However, the Na+ level did not improve, and signs of dehydration emerged. On the seventh day of the illness, drinking water restriction was discontinued, and 3% sodium chloride fluid replacement was initiated. The patient subsequently followed a favorable course, and the Na+ level remained normal even after fluid replacement was discontinued. It is important to differentiate between SIADH and cerebral salt wasting syndrome (CSWS), as the treatment of the two are diametrically opposite. However, distinguishing between these two diseases at an early onset can be difficult, as they have very similar laboratory findings. CSWS can occur in patients with minor head injury, as in the present case, so we should bear this disease in mind as a differential diagnosis, even when imperceptible graduations are recognized in patients.