Guillain-Barre syndrome is an ascending paralysis with absent deep tendon reflexes that is usually preceded by an upper respiratory infection or infectious diarrhea. It is diagnosed based on clinical presentation of muscle weakness, decreased reflexes, and sometimes a rash, as well as cerebrospinal fluid analysis showing increased white blood cells and protein with normal glucose and red blood cell counts. Common preceding infections include Campylobacter jejuni and viruses like West Nile and HSV that can cause aseptic meningitis.