ABSTRACT
Cerebral Salt Wasting Syndrome (CSW) is an uncommon cause of hypotonic hyponatremia associated to central nervous system disease (especially subarachnoid hemorrhage) and characterized by hypovolemia due to renal sodium loss. The main differential diagnosis is SIADH, a much more common form of hyponatremia without signs of hypovolemia. The treatment is based on filling with isotonic or hypertonic saline. We report the case of a 50-year-old chinese man with a history of arterial hypertension presenting to the ER for headache and fever after vaccination for SARS-CoV-2. In the ER he was hemodynamically stable without neurological deficits. Blood tests showed severe hypoosmolar hyponatremia. Brain CT revealed multiple hypodense oval areas of uncertain nature with peripheral contrast enhancement. The main microbiological tests were negative. In the suspicion of paraneoplastic SIADH, water restriction was prescribed and a total body CT scan was performed, resulting normal. Nevertheless, hyponatremia got worse. Brain MRI revealed signs of subacute intracranial bleeding and angiography showed an anterior cerebral artery aneurysm. An echocardiography revealed collapse of the inferior vena cava, therefore, given the hypovolemia, hypotonic hyponatremia and the signs of recent brain injury, diagnosis of CSW was made. Treatment was based on endovascular coiling of the aneurysm and correction of hypovolemic hyponatremia using isotonic saline. It is essential to differentiate between CWS and SIADH since the treatment is categorically different. Their key distinguishing feature is volemia.