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

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/s(2) ( mean 0.937 +/- 0.17 mm/s(2)). ADC values of ADEM lesions in the acute stage were in the range 0.37-0.68 x 10(-3) mm/s(2) ( mean 0.56 +/- 0.16 mm/s(2)) and 1.01-1.31 x 10(-3) mm/s(2) ( mean 1.24 +/- 0.13 mm/s(2)) 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.