Acute disseminated encephalomyelitis (ADEM)

An 18-year-old man was admitted to the emergency department with five day-neurological symptoms consistent of motor dysfunction, right hand clumsiness and dysarthria. The previous days he had had cough and expectoration without fever.
Both blood test and cerebrospinal fluid obtained through lumbar puncture were normal. Antibodies were also negative.

Unenhanced CT (Fig. 1) demonstrated ill-defined hypointensities at midbrain, basal ganglia and internal capsules.

FLAIR (Fig. 2) and T2WI (Fig. 3) showed patchy areas of confluent increased intensity affecting white and deep gray matter, with special predilection for the midbrain, caudate and lenticular nuclei.

After contrast administration (Fig. 4) some lesions revealed peripheral with “incomplete ring” morphology enhancement.

In control MR (Fig. 5) showed significant improvement of the confluent hyperintensities with no enhacement after contrast administration.

Acute disseminated encephalomyelitis (ADEM) is a low-incidence (0.4/100.000) inflammatory demyelinating disorder of the central nervous system. It typically affects children or adolescents with no gender predilection [1]. Exact pathogenesis of the disease is unknown; although it is thought that a T cell mediated autoimmune response to myelin basic protein, triggered by an infection or vaccination, underlies its pathogenesis.

Clinical manifestations appear 1-2 weeks after a viral infection or vaccination. The most characteristic features are the development of multifocal neurological symptoms (ataxia, tremor, optic neuritis, convulsions...) with a variable prodromal phase consisting of headache, fever and nausea with vomiting. [2]

Unlike multiple sclerosis, ADEM usually course as a monophasic disease. In fact, any new or fluctuating symptoms during the first 3 months are considered to be part of the same event. Appearance of new lesions at MRI suggests the diagnosis of multiphasic ADEM or multiple sclerosis (MS).

Diagnosis of acute disseminated encephalomyelitis is based on clinical and radiological features because there is no specific biological marker or confirmatory test.

In acute phase, CT can be unremarkable in up to 40% of the cases.

Conventional MRI demonstrate at FLAIR and T2 WI patchy areas of increased signal intensity involving white and gray matter, particularly basal ganglia, thalami and brainstem. Lesions tend to be multiple, bilateral and with no mass effect. Compared to MS, ADEM lesions tend to be more rounded and larger with poorly defined margins. Corpus callosum involvement is more characteristic of MS; meanwhile thalamic participation is more typical of ADEM [3, 4].
Spinal cord lesions are common and affect multiple segments.

Treatment consists of methylprednisolone and immunoglobulin or cyclophosphamide for refractory patients. Most patients have excellent outcome with no neurological impairment. Only a minority of patients presents neurological sequelae such as motor disability, visual loss or epilepsy.