Inflammation in ADEM is widely disseminated and ill-defined, and finally, lesions are strictly perivenous, while in MS they are disposed around veins, but not so sharply.Nevertheless, the co-occurrence of perivenous and confluent demyelination in some individuals suggests pathogenic overlap between acute disseminated encephalomyelitis and multiple sclerosis and misclassification even with biopsy or even postmortem  ADEM in adults can progress to MS

Multiphasic disseminated encephalomyelitis
When the person has more than one demyelinating episode of ADEM, the disease is then called recurrent disseminated encephalomyelitis or multiphasic disseminated encephalomyelitis (MDEM). It has been found that anti-MOG auto-antibodies are related to this kind of ADEMAnother variant of ADEM in adults has been described, also related to anti-MOG auto-antibodies, has been named fulminant disseminated encephalomyelitis, and it has been reported to be clinically ADEM, but showing MS-like lesions on autopsy. It has been classified inside the anti-MOG associated inflammatory demyelinating diseases. Acute hemorrhagic leukoencephalitis
Acute hemorrhagic leukoencephalitis (AHL, or AHLE), acute hemorrhagic encephalomyelitis (AHEM), acute necrotizing hemorrhagic leukoencephalitis (ANHLE), Weston-Hurst syndrome, or Hursts disease, is a hyperacute and frequently fatal form of ADEM. AHL is relatively rare (less than 100 cases have been reported in the medical literature as of 2006), it is seen in about 2% of ADEM cases, and is characterized by necrotizing vasculitis of venules and hemorrhage, and edema. Death is common in the first week and overall mortality is about 70%, but increasing evidence points to favorable outcomes after aggressive treatment with corticosteroids, immunoglobulins, cyclophosphamide, and plasma exchange.
These are considered alternative therapies, used when corticosteroids cannot be used or fail to show an effect.There is some evidence to suggest that patients may respond to a combination of methylprednisolone and immunoglobulins if they fail to respond to either separately
In a study of 16 children with ADEM, 10 recovered completely after high-dose methylprednisolone, one severe case that failed to respond to steroids recovered completely after IV Ig; the five most severe cases – with ADAM and severe peripheral neuropathy – were treated with combined high-dose methylprednisolone and immunoglobulin, two remained paraplegic, one had motor and cognitive handicaps, and two recovered. A recent review of IVIg treatment of ADEM (of which the previous study formed the bulk of the cases) found that 70% of children showed complete recovery after treatment with IVIg, or IVIg plus corticosteroids. A study of IVIg treatment in adults with ADEM showed that IVIg seems more effective in treating sensory and motor disturbances, while steroids seem more effective in treating impairments of cognition, consciousness and rigor. This same study found one subject, a 71-year-old man who had not responded to steroids, that responded to an IVIg treatment 58 days after disease onset. Prognosis
Full recovery is seen in 50 to 70% of cases, ranging to 70 to 90% recovery with some minor residual disability (typically assessed using measures such as mRS or EDSS), average time to recover is one to six months. The mortality rate may be as high as 5–10%.