Imaging of Acute Disseminated Encephalomyelitis

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Acute disseminated encephalomyelitis (ADEM) is a monophasic demyelinating disease of the central nervous system typically affecting the gray and the white matter of the brain and spinal cord in multiple locations. In the acute stages, ADEM is characterized histologically by perivenous edema, demyelination, and infiltration with macrophages and lymphocytes, with relative axonal sparing, whereas the late course of the disease is characterized by perivascular gliosis.

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Pathogenesis

The pathogenesis of ADEM is debated despite the large number of theories proposed, even though there is general consensus that ADEM is an immune-mediated disorder resulting from an autoimmune reaction to myelin. The most compelling evidence perhaps is represented by the similarities of ADEM to experimental allergic encephalomyelitis, in which damaged myelin exposes segregated antigens that in turn induce an immune response. Two basic mechanisms currently are under consideration [2]:

  • 1.

    Inflammatory

Clinical and laboratory findings

ADEM most commonly affects young and adolescent children, with a 0.8 per 100,000 population per year incidence and no gender preponderance [2]. A greater prevalence during the winter months is recorded, probably in association with a higher incidence of upper airway infections in winter [5]. It commonly is accepted that the incidence in adult and elderly age groups is significantly lower [2].

The clinical presentation of ADEM is widely variable, ranging from an acute presentation with seizures

Neuroimaging

The neuroradiologic findings of ADEM are not specific and typically do not allow differentiation of ADEM from MS or encephalitis. CT typically is unrevealing unless large lesions are present, in which case a faint hypodensity may be detected (Fig. 1). As a consequence, in presence of suggestive clinical findings MRI should be obtained.

Conventional MRI findings typically include multiple, asymmetrically distributed, poorly marginated, hyperintense areas on T2-weighted and fluid-attenuated

Variants of acute disseminated encephalomyelitis and classification issues

Although ADEM is, by definition, a monophasic disease, studies show that as many as one third of patients experience relapses in the future [8]. It still is problematic to distinguish these cases from a relapsing-remitting form of MS and to predict which patients will suffer from recurrent disease bouts. Moreover, although lesions of ADEM typically are reversible, more aggressive variants exist. Therefore, it has become clear that there is a broad spectrum of central nervous inflammatory and

Acute relapsing disseminated encephalomyelitis, biphasic disseminated encephalomyelitis, and multiphasic disseminated encephalomyelitis

The real significance of the relapsing-remitting variants of ADEM still is questioned in that they may represent intermediate forms between ADEM and MS; this would strengthen the concept of a common pathophysiologic spectrum [20], [21]. According to the proposals of the International Pediatric MS Study Group [22], the definition of acute relapsing disseminated encephalomyelitis (ARDEM) requires a second attack more than 3 months after the initial event (1 or more months after steroid

Acute hemorrhagic encephalomyelitis

Lesions of ADEM may be explained prevalently by a microvascular inflammatory pathologic mechanism. When the degree of inflammation leads to a stage of necrotizing vasculitis, a hyperacute form of ADEM characterized by ball, ring-shaped, or confluent hemorrhages and necrosis of vascular wall with fibrin deposition and neutrophilic infiltration. Clinical presentation of acute hemorrhagic encephalomyelitis (AHEM) is severe with reduced consciousness, hemiparesis, aphasia, brainstem dysfunction,

Acute necrotizing encephalopathy

AHEM seen in Western populations probably has some relationship with acute necrotizing encephalopathy of childhood (ANEC), a rare devastating complication of influenza and other viral infections that prevails in Eastern Asia and has a bleak prognosis with elevated mortality. ANEC has been related to intracranial cytokine storms causing blood-brain barrier damage that results in edema and necrosis, without signs of direct viral invasion or parainfectious demyelination. MRI findings involve a

Differential diagnosis

When assessing patients who have suspected ADEM, the most obvious concern is the differentiation from an onset of MS. This is a major problem for which there seems to be no established solution based on current knowledge. Studies show that approximately one fourth of patients who have ADEM develop a classical relapsing form of MS in the subsequent 2 to 5 years [27], but these patients are difficult to identify on initial presentation. Several clinical, biologic, and radiologic differences

References (27)

  • F. Dubreuil et al.

    [Acute disseminated encephalomyelitis preceding cutaneous lupus]

    Rev Med Interne

    (1998)
  • M.L. Tsai et al.

    Multiphasic disseminated encephalomyelitis mimicking multiple sclerosis

    Brain Dev

    (1996)
  • R.D. Adams et al.

    Principles of neurology

    (1989)
  • T. Menge et al.

    Acute disseminated encephalomyelitis: an update

    Arch Neurol

    (2005)
  • M. Yamada et al.

    Paraneoplastic encephalo-myelo-ganglionitis: cellular binding sites of the antineuronal antibody

    Acta Neuropathol

    (1994)
  • R.C. Dale et al.

    Acute disseminated encephalomyelitis, multiphasic disseminated encephalomyelitis and multiple sclerosis in children

    Brain

    (2000)
  • S. Tenembaum et al.

    Acute disseminated encephalomyelitis. A long-term follow-up study of 84 pediatric patients

    Neurology

    (2002)
  • J.L. Hynson et al.

    Clinical and neuroradiological features of acute disseminated encephalomyelitis in children

    Neurology

    (2001)
  • J. Kesselring et al.

    Acute disseminated encephalomyelitis. MRI findings and the distinction from multiple sclerosis

    Brain

    (1990)
  • M. Gallucci et al.

    Acquired inflammatory white matter diseases

    Childs Nerv Syst

    (2001)
  • P.A. Baum et al.

    Deep gray matter involvement in children with acute disseminated encephalomyelitis

    AJNR Am J Neuroradiol

    (1994)
  • A. Rovira Canellas et al.

    Idiopathic inflammatory-demyelinating diseases of the central nervous system

    Neuroradiology

    (2007)
  • J. Honkaniemi et al.

    Delayed MR imaging changes in acute disseminated encephalomyelitis

    AJNR Am J Neuroradiol

    (2001)
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