There is often an infection that occurs before the diagnosis of ADEM, or even an immunisation, the interval varying between several days up to one month, the average being one to two weeks. In a minority of cases there is no clear preceding illness. At the beginning, symptoms can be non-specific but nonetheless worrying, such as fever, headache, stiff neck, a loss of appetite and vomiting. This is usually followed by or accompanied with a decreased conscious level such that the child may seem confused, lethargic or drowsy and does not respond in their normal way. For a diagnosis of ADEM to be made, a child's level of consciousness must be affected and this is referred to as 'acute encephalopathy'. At times the child can even slip into coma.
Other symptoms include:
- difficulties standing or walking
- hemiparesis (weakness down one side of the body)
- balance problems or ataxia (unsteadiness)
- cranial nerve palsies (paralysis of the nerves that emerge directly from the brain)
- visual impairment or visual loss due to inflammation of the optic nerve (eg optic neuritis) often involving both eyes
- epileptic seizures (these are more common in the younger child - five years old or younger).