[Sudden hyponatremia with unconsciousness. Case report and brief overview of the syndrome of inadequate antidiuresis (SIAD or Schwartz-Bartter syndrome].

A sixty-six year old female was admitted to the hospital with an incomplete hemiparesis on the left side combined with a short episode of unconsciousness. According to her husband's account she had a seizure. Relevant laboratory measurements: plasma sodium concentration 113.9 mmol/l, plasma concentration of ADH 10.3 pg/ml, urine sodium concentration 44.4 mmol/l. The plasma concentrations of creatinine and urea were within normal limits. The working hypothesis was SIAD (syndrome of inappropriate antidiuresis) or Schwartz-Bartter-syndrome. The patient was treated immediately with water restriction (500-1000 ml/day), furosemide and i.v. replacement of urinary sodium losses by 3% NaCl. The analysis of cerebrospinal fluid showed pleocytosis and increased concentrations of immunoglobulins G and M. Serological diagnosis was positive for antigen of varicella-zoster virus. These observations were thought to be compatible with a diagnosis of SIAD in the setting of encephalitis. Under water restriction, infusion of 3% saline, treatment with loop diuretics and aciclovir (3 x 750 mg daily) the neurological function returned to normal within 2 days. A standard oral water load on the 14th hospital days showed a return to a normal water metabolism.