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 are often non-specific, such as fever, headache, stiff neck, a loss of appetite and vomiting. This is followed by a decreased conscious level (eg the child may seem confused, lethargic or drowsy and 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:
- hemiparesis (weakness down one side of the body)
- 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
- seizures (these are more common in the younger child - five years old or younger).