Life-threatening hyponatremia due to the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in a patient with the miller fisher syndrome.

We report a life-threatening hyponatremia due to SIADH which developed suddenly in a patient with the Miller Fisher syndrome (a variant of Guillian Barré syndrome characterized by complete ophthalmoplegia, ataxia, and areflexia). A 55 year-old female was admitted with a clinical picture of the Miller Fisher syndrome. Cerebrospinal fluid was acellular with elevated proteins, and electromyographic changes were characteristic of polyneuropathy. On the third day of admission the patient was found to be mentally confused with a serum sodium of 108 mmol/L. Serum osmolality was 236 mosm/L and urine osmolality was 636 mosm/L. Urine sodium was 103 mmol/L. The serum sodium normalized after treatment with a single dose of intravenous furosemide, hypertonic saline infusion and fluid restriction. To our knowledge, this is the first description of SIADH developing in a patient with the Miller Fisher syndrome.