Many first notice something is wrong after a recent infection or vaccination when, over a day or two, sudden neurologic symptoms appear—intense headache, fever, profound fatigue, confusion or sleepiness, and new problems with balance, vision, or limb weakness. In children especially, seizures or rapid changes in behavior or alertness can be early red flags that prompt an urgent hospital visit. Doctors often suspect ADEM and later confirm anti‑MOG antibody involvement with MRI brain/spine scans and blood tests, so the “first signs of acute disseminated encephalomyelitis with anti‑MOG antibodies” are typically these abrupt, widespread neurologic changes following a trigger.