Acute disseminated encephalomyelitis following 2009 H1N1 influenza vaccination.

Since the worldwide spread of the novel influenza type A virus in 2009, trivalent vaccines against H1N1 (pandemic) 09 and seasonal influenza have been used. We describe a 33-year-old woman who presented with hypoesthesia below the Th7 level fifteen days after vaccination without any preceding infection. Cerebrospinal fluid showed an increased level of myelin basic protein and positive oligoclonal IgG bands. Magnetic resonance imaging revealed disseminated lesions in the brain and thoracic cord. Steroid therapy improved her symptoms. She was diagnosed as having acute disseminated encephalomyelitis (ADEM) possibly related to the vaccination. As a potential adverse effect of the influenza vaccine, in addition to Guillain-Barré syndrome, ADEM should also be recognized.