Acute disseminated encephalomyelitis (ADEM)

Additionale clinical history: A 23-month-old male with 2 weeks of viral symptoms presenting with progressive weakness and inability to walk.


Findings

Figure 1, Figure 2, and Figure 3: Axial FLAIR images demonstrate increased signal intensity in the centrum semiovale (Figure 3), putamen (Figure 2) and thalamus (Figure 2) as well as the dentate nuclei (Figure 1).
Figure 4: T1 weighted post gadolinium axial image demonstrates no evidence of enhancement.


Diagnosis: Acute Disseminated Encephalomyelitis (ADEM)


ADEM is thought to be a postviral leukoencephalopathy of children and young adults mediated by an allergic or autoimmune cross-reaction with an antigen. The patient typically presents with confusion, headaches, seizures and/or focal neurological symptoms occurring within 2 or 3 weeks of a recent viral infection, vaccination, respiratory infection or exanthematous disease of childhood. Epstein-Barr virus, cytomegalovirus and Mycoplasma pneumoniae are the most common pathogens associated with ADEM. The diagnosis can be made by clinical history and CSF analysis. CSF analysis may demonstrate an increase in white cells with lymphocyte predominance and an increase in myelin basic protein.

On MR, ADEM demonstrates multiple foci of high signal intensity on FLAIR and T2 weighted images in the white matter, especially subcortically. The cortical gray matter is usually spared though deep gray matter lesions are occasionally observed. Gadolinium T1 weighted images may demonstrate enhancement in a nodular or ring like pattern. ADEM can also affect the spinal cord or brain stem. The main differential to consider is multiple sclerosis as the imaging characteristics and clinical presentation may overlap. Because ADEM is generally considered a monophasic disease, a follow-up MR 6 months after the start of the disease should not reveal any new lesions. Although patients with ADEM are at a slight increased risk for recurrence, if new lesions are found multiple sclerosis should be strongly considered.

The treatment of ADEM is the administration of corticosteroids. The resolution of neurological deficits is often seen within one month of onset of the disease (80-90%), however, permanent neurological damage may occur (10-20%).