Most ADEM presentations can be categorized into 7 clinical syndromes: mild encephalopathy, severe encephalopathy, predominantly brainstem presentation, hemiparesis/long tract signs, predominantly ataxic, transverse myelitis, and encephalomyeloradiculoneuropathy, which is a syndrome that combines upper and lower motor neuron signs. The patient in this case had both upper and lower motor neuron involvement and was categorized as having encephalomyeloradiculoneuropathy.
Differentiating ADEM from multiple sclerosis (MS) is important. History of a preceding infectious illness or immunization, association with constitutional symptoms such as fever, and prominence of cortical signs such as mental status changes and seizures all favor ADEM. Cerebellar abnormalities that are common in MS are rare in ADEM. The age of onset is younger than 11 or 12 years in ADEM and older than 11 or 12 years in MS.
Early recognition is important so that appropriate therapy can be started. Laboratory studies of most patients with ADEM evidence nonspecific inflammation in the form of lymphocytosis or an increased erythrocyte sedimentation rate or C-reactive protein, although these findings can be very nonspecific. Lumbar puncture and CSF examination usually reveal a normal opening pressure with mild pleocytosis and/or a modest increase in protein concentration consistent with ongoing inflammation, as was seen in this case. In some patients, the CSF may be normal. Some patients with ADEM may have oligoclonal bands. CSF myelin basic protein levels may be increased, indicating demyelination.[1,6,7]
Electroencephalography is not diagnostic for ADEM. It may reveal increased background slow wave activity that is typical of an encephalopathy, but epileptic activity is rarely seen.[11,13] In patients with optic neuritis, visual evoked potentials may be prolonged. Nerve conduction studies are indicated in patients with lower motor neuron signs, as in this case. Patients may have a demyelinating neuropathy with prolonged F waves, slower conduction velocities, and prolonged distal latencies. Conduction blocks are usually not observed. Features consistent with an axonal neuropathy may be seen in rare cases.[10,11]
Imaging studies of the central nervous system are important in establishing the diagnosis of ADEM. MRI of the brain with contrast is the imaging modality of choice. CT scanning of the brain is less sensitive and is often normal. MRI abnormalities are best defined by T2-weighted images and FLAIR sequences. The lesions are typically bilateral and asymmetric and tend to be poorly marginated, located in the deep and subcortical white matter, and have relative periventricular sparing.[1,2,6,7] Acute lesions are sometimes enhanced by contrast. In patients with features suggestive of spinal cord dysfunction, an MRI of the spine may be helpful. It may show swelling of the cord, especially on T2-weighted sequences in cases of myelitis. Demyelinating plaques may be seen, and contrast enhancement with gadolinium may be noted.
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