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Diffusion-weighted imaging and proton MR spectroscopy in the characterization of acute disseminated encephalomyelitis
K S Balasubramanya1, J M E Kovoor, P N Jayakumar
1Department of Neuroimaging and Interventional Radiology, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka 560029, India.
Introduction:
Acute disseminated encephalomyelitis (ADEM) is usually a monophasic illness characterized by multiple lesions involving gray and white matter. Quantitative MR techniques were used to characterize and stage these lesions.
Methods:
Eight patients (seven males and one female; mean age 19 years, range 5 to 36 years) were studied using conventional MRI (T2- and T1-weighted and FLAIR sequences), diffusion-weighted imaging (DWI) and proton magnetic resonance spectroscopy (MRS). Apparent diffusion coefficient (ADC) values and MRS ratios were calculated for the lesion and for normal-appearing white matter (NAWM). Three patients were imaged in the acute stage (within 7 days of the onset of neurological symptoms) and five in the subacute stage (after 7 days from the onset of symptoms).
Results:
ADC values in NAWM were in the range 0.7-1.24 x 10(-3) mm/s2 (mean 0.937 +/- 0.17 mm/s2). ADC values of ADEM lesions in the acute stage were in the range 0.37-0.68 x 10(-3) mm/s2 (mean 0.56 +/- 0.16 mm/s2) and 1.01-1.31 x 10(-3) mm/s2 (mean 1.24 +/- 0.13 mm/s2) in the subacute stage. MRS ratios were obtained for all patients. NAA/Cho ratios were in the range 1.1-3.5 (mean 1.93 +/- 0.86) in the NAWM. NAA/Cho ratios within ADEM lesions in the acute stage were in the range 0.63-1.48 (mean 1.18 +/- 0.48) and 0.29-0.84 (mean 0.49 +/- 0.22) in the subacute stage. The ADC values, NAA/Cho and Cho/Cr ratios were significantly different between lesions in the acute and subacute stages (P < 0.001, P < 0.027, P < 0.047, respectively). ADC values were significantly different between lesions in the acute (P < 0.009) and subacute stages (P < 0.005) with NAWM. In addition, NAA/Cho and Cho/Cr ratios were significantly different between lesions in the subacute stage and NAWM (P < 0.006, P < 0.007, respectively).
Conclusion:
ADEM lesions were characterized in the acute stage by restricted diffusion and in the subacute stage by free diffusion and a decrease in NAA/Cho ratios. Restricted diffusion and progressive decrease in NAA/Cho ratios may help in staging the disease.
Insights
Acute disseminated encephalomyelitis (ADEM) lesions show restricted diffusion in the acute stage and free diffusion in the subacute stage. Magnetic resonance spectroscopy (MRS) changes help in staging ADEM disease progression.
Area of Science:
- Neurology
- Radiology
- Neuroimaging
Background:
- Acute disseminated encephalomyelitis (ADEM) is typically a monophasic illness with multifocal gray and white matter lesions.
- Quantitative MRI techniques are crucial for characterizing and staging ADEM lesions.
Purpose of the Study:
- To characterize and stage ADEM lesions using quantitative MRI techniques.
- To differentiate between acute and subacute stages of ADEM.
Main Methods:
- Eight patients with ADEM underwent conventional MRI, diffusion-weighted imaging (DWI), and proton magnetic resonance spectroscopy (MRS).
- Apparent diffusion coefficient (ADC) values and MRS ratios (NAA/Cho, Cho/Cr) were calculated for lesions and normal-appearing white matter (NAWM).
- Patients were categorized into acute (within 7 days) and subacute (after 7 days) stages.
Main Results:
- Acute ADEM lesions exhibited restricted diffusion (lower ADC values) compared to NAWM.
- Subacute ADEM lesions showed free diffusion (higher ADC values) and decreased NAA/Cho ratios.
- Significant differences in ADC values and MRS ratios were observed between acute and subacute ADEM lesions and NAWM.
Conclusions:
- ADEM lesions are characterized by restricted diffusion in the acute stage and free diffusion with decreased NAA/Cho ratios in the subacute stage.
- Quantitative MRI parameters, including ADC values and MRS ratios, can effectively aid in staging ADEM disease progression.
