[Herpes simplex encephalitis complicated with cerebral salt wasting syndrome: a case study].

A 78-year-old man was admitted to the hospital with a 4-day history of fever and confusion. Physical examination revealed oral dryness and decreased skin turgor. Blood tests showed hyponatremia (121.5 ‍mEq/l), and cerebrospinal fluid examination revealed positivity for herpes simplex virus 1 (HSV-1) via polymerase chain reaction. He was diagnosed with herpes simplex encephalitis and initiated acyclovir treatment. The hyponatremia was diagnosed as cerebral salt wasting syndrome (CSWS) and treated with hypertonic saline infusion and fludrocortisone. The cerebrospinal fluid HSV-1 DNA became negative, and the serum sodium levels normalized. Hyponatremia complicated with encephalitis is often caused by the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), whereas CSWS is rare, mostly observed in tuberculous meningitis. Differentiating between the SIADH and CSWS is important as they require distinct therapeutic strategies.