Diffusion-weighted imaging and proton MR spectroscopy in the characterization of acute disseminated encephalomyelitis.
BACKGROUND
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).


CONCLUSIONS
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.
Balasubramanya
K S
KS
Department of Neuroimaging and Interventional Radiology, National Institute of Mental Health and Neurosciences, Bangalore, Karnataka 560029, India.
Kovoor
J M E
JM
Jayakumar
P N
PN
Ravishankar
S
S
Kamble
R B
RB
Panicker
J
J
Nagaraja
D
D
D000293:Adolescent; D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D002794:Choline / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D038524:Diffusion Magnetic Resonance Imaging; D004673:Encephalomyelitis, Acute Disseminated / Q000175:diagnosis* / Q000378:metabolism; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013997:Time Factors
D001224:Aspartic Acid; C000179:N-acetylaspartate; D003401:Creatine; D002794:Choline