A Case of Miller-Fisher Syndrome with Syndrome of Inappropriate Secretion of Antidiuretic Hormone

We report a 72-year-old woman with Miller-Fisher syndrome (MFS) with syndrome of inappropriate secretion of antidiuretic hormone (SIADH). She developed diplopia and unsteady gait a week after an upper respiratory infection. Neurologic examination revealed ophthalmoplegia, ataxia, symmetrical weakness, numbness, and areflexia. She underwent intravenous immunoglobulin therapy. Her serum sodium concentration decreased to 119 mEq/L on day 12. She had low plasma osmolarity (254 mosm/kg), high urine osmolarity (457 mosm/kg), and high urine sodium level (73 mEq/L), while the blood level of antidiuretic hormone was normal. Anti-GD1b immunoglobulin G (IgG), -GQ1b IgG, -GT1a IgG, and -Gal-C IgM antibodies were positive. We diagnosed her with MFS overlapping with SIADH. Four weeks after onset, her symptoms recovered. The elevation of anti-GD1b, -GQ1b, and -GT1a antibodies that recognize disialosyl residue may be pathologically related to SIADH.