[Hyponatremia with high plasma ANP level--report of two cases with emphasis on the pathophysiology of cerebral salt wasting].

Two cases of hyponatremia with intracranial lesions are reported with emphasis on diagnostic value of measurement of antidiuretic hormone (ADH) and atrial natriuretic polypeptide (ANP). Case 1. A 77-year-old female was transferred to our hospital for further care of vegetative state after subarachnoid bleeding on May 23, 1986. She was operated by neck clipping of rt-IC bifurcation aneurysm and lt-internal carotid-posterior communicating aneurysm at another hospital. On admission, computed tomography showed diffuse low density at bilateral thalamus and centrum semiovale. Biochemical analysis revealed hyponatremia (120 mEq/t) with increased natriuresis. Endocrinological date revealed normal plasma ADH and high plasma ANP levels. Patient was treated with infusion of 1% NaCl. Case 2. A 65-year-old male was admitted to our department because of gradual impairment of consciousness and generalized convulsion. Computed tomography showed small low density area at rt-thalamus and lt-cerebellar hemisphere. Biochemical date revealed severe hyponatremia (91 mEq/t) with normal plasma level of ADH and high plasma ANP. He was treated with infusion of 3% NaCl and hyponatremia was improved. The hyponatremia is frequently associated with intracranial disorders such as brain tumor, subarachnoid hemorrhage and head injury. Originally, hyponatremia with natriuresis was thought to be caused by salt wasting. This syndrome was defined as the inability to prevent salt loss in the urine due to undefined natriuretic factor in the brain. However, since 1957, because of introduction of concept of SIADH, it has generally become accepted that patients with natriuresis had SIADH. (ABSTRACT TRUNCATED AT 250 WORDS)