ABSTRACT
<b>Introduction：</b>Hyponatremia, which is frequently present in patients with end-stage cancer, causes delirium and disturbance of consciousness and is considered a poor prognostic factor. We report a case of hyponatremia with hypopituitarism in association with leptomeningeal metastasis, resulting in reversible disturbance of consciousness. <b>Case report：</b>A 77 year-old female received chemotherapy at our hospital for postoperative recurrence of lung cancer, and best supportive care due to a side effect. After transfer to another hospital, she experienced a sudden disturbance of consciousness and was returned to our hospital. A detailed examination resulted in a diagnosis of hyponatremia from hypopituitarism following leptomeningeal metastasis involving the cerebral ventricles. Hyponatremia was improved by NaCl supplement and hormone replacement, followed by recovery from disturbance of consciousness. <b>Discussion：</b>QOL of patients with end-stage cancer can be improved through the active treatment of reversible causes of disturbance of consciousness.<b> Conclusion：</b>When severe hyponatremia is detected in cancer patients, it is important to consider the possibility of hypopituitarism with brain metastasis or meninges dissemination in the differential diagnosis.