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Home arrow Environment arrow Inflammatory Disorders of the Nervous System: Pathogenesis, Immunology, and Clinical Management
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Diagnosis

Diagnostic criteria for ADEM both from 2007 to 2012 are cited in Table 7.1 [1]. In patients with ADEM, certain nonspecific markers such as platelet counts and sedimentation rate can be increased as in most other autoimmune diseases. Examination of CSF may be unremarkable; however, it usually demonstrates elevated protein concentration (usually between 0.5 and 1.0 g/dL) and lymphocytic pleocytosis (between 50 and 200 cells/mm3). The oligoclonal bands are less commonly observed than in MS and are more frequently found in adults than children with ADEM. In a minority of patients with ADEM, increases in CSF immunoglobulins can be detected. Serum anti-aquaporin-4 IgG antibody is absent, while serum anti-MOG (myelin oligodendrocyte glycoprotein) antibodies may be present transiently. Certain nonspecific markers of inflammation such as elevated IgG index and increased myelin basic protein level are occasionally detected. In some patients with ADEM, virologic investigation of the CSF and/or serum may reveal the presence of certain viral protein and other viral biomarkers, which have been associated with development of ADEM.

Neuroimaging is one of the most significant diagnostic tests for ADEM. CT scan of the brain may be unremarkable or at best demonstrates areas of nonspecific low attenuation involving subcortical white matter. These affected areas may or may not enhance following infusion of the CT contrast. MRI of the brain and spinal cord with and without contrast is a more informative diagnostic tool and plays a major role in establishing the diagnosis of ADEM and excluding some of its differential diagnoses. Indeed, observing giant and disseminated demyelinating lesions on brain and spinal MR imaging strongly supports a diagnosis of ADEM; however, brain tumors and tumefactive MS can also present similarly.

According to the IPMSSG, typically, MRI shows diffuse or multifocal, poorly demarcated, large, (>1-2 cm) hyperintense lesion(s) on T2-weighted as well as fluid- attenuated inversion recovery (FLAIR) sequences involving predominantly the cerebral white matter as well as deep gray matter lesions, and infratentorial structures (mainly thalami and basal ganglia) can be detected (Figs. 7.1, 7.2, 7.3, and 7.4) [12]. White matter lesions which manifest as hypointense signals on Tl-weighted images

T2-weighted axial view of brain of a patient with ADEM which demonstrates multiple large hyperintense lesions involving mainly the white matter (From Dale [8] Copyright permission obtained)

Fig. 7.1 T2-weighted axial view of brain of a patient with ADEM which demonstrates multiple large hyperintense lesions involving mainly the white matter (From Dale [8] Copyright permission obtained)

(a-l) Axial fluid-attenuated inversion recovery (FLAIR) images through the infratentorial regions of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

Fig. 7.2 (a-l) Axial fluid-attenuated inversion recovery (FLAIR) images through the infratentorial regions of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

are uncommon but not unheard of. A single diffuse bilateral symmetric large lesion involving the deep gray matter is occasionally present. Infrequently, these can exert mass effect. In such cases, neurosurgical biopsy should be considered to exclude glioma and other primary or metastatic brain tumors, infective processes, and other inflammatory diseases. The presence of hypointense lesions on T1-weighted images, particularly if persistant, with the presence of two or more periventricular lesions should suggest a diagnosis of MS rather than ADEM [1].

Based on our observations of our patients with ADEM, these MRI abnormal signals are often larger than MS lesions, more symmetric, lack well-defined margins, and can involve the subcortical gray matter - the basal ganglia and thalami (Fig. 7.5). Some of the ADEM lesions reveal enhancement on post-contrast Tl-weighted sequence (14-30%), and usually their pattern of enhancement is more homogeneous than MS lesions. Following treatment, repeat MRI of the brain does not show development of new lesions and only reveals significant resolution of old lesions. Interestingly, MRI of the brain also assists neurologists to search for certain features

(a-l) Axial FLAIR images at the level of the basal ganglia and thalamus of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

Fig. 7.3 (a-l) Axial FLAIR images at the level of the basal ganglia and thalamus of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

such as location and symmetry of distribution of the demyelinating lesions with the relative absence of periventricular lesions and presence of deep gray matter lesions, which are not typically seen in MRI of MS patients.

Proton MR spectroscopy (H-MRS) is an advanced neuroimaging technique which has been utilized to study patients with ADEM. In acute stage of ADEM, H-MRS reveals increase in lipid with decrease in myoinositol/creatinine ratio with unchanged N-acetylaspartate (NAA) or choline concentrations [17, 18]. With further underlying disease progression, decline in NAA and increase of choline concentrations in regions, where hyperintense T2-weighted abnormal signals are present, are detected [17, 19].

The differential diagnoses of ADEM consist of long list of acute diseases or disorders which cause leukoencephalopathy and either clinically or neuroradiologically imitate ADEM. The differential diagnoses of AHLE include ADEM, tumefac- tive MS, acute necrotizing encephalitis of childhood, Leigh syndrome, vanishing white matter disease, or toxic meningoencephalitis.

(a-l) Axial FLAIR images through the cerebral convexities of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

Fig. 7.4 (a-l) Axial FLAIR images through the cerebral convexities of 12 children with ADEM (From Marin and Callen [12] Elsevier, Inc. Copyright permission obtained)

 
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