People often first notice acute disseminated encephalomyelitis (ADEM) without anti‑MOG antibodies after a recent infection or, less often, a vaccination, when sudden neurologic symptoms develop over hours to days—high fever, severe headache, confusion or sleepiness, unsteady walking, vision changes, or new weakness or numbness on one side of the body. In children and young adults, families may see abrupt behavior changes, seizures, or trouble speaking, prompting an urgent evaluation; doctors typically recognize the pattern with a neurologic exam and brain MRI showing widespread inflammation. These first signs of acute disseminated encephalomyelitis without anti‑MOG antibodies usually appear as a single, rapidly evolving episode rather than slowly progressive symptoms.