The Evaluation of MRI Diffusion Values of Active Demyelinating Lesions in Multiple Sclerosis
The importance of new radiologic activity on MRI in the early diagnosis and monitoring of the course of Multiple Sclerosis (MS) is indicated in several guidelines. Gadolinium (Gd) enhancement of lesions is the main surrogate marker to screen this activity, but there are some safety, financial and technical limitations for Gd administration. Diffusion weighted imaging (DWI) is a safer and routinely accessible method that may be used for screening of active lesions and is sometimes used as an alternative to Gd enhancing images.
The purpose of this study was to investigate the relationship of DWI characteristics to the status of enhancement in demyelinating lesions of MS patients.
This is a retrospective cohort study of registered patients in the Ottawa Multiple Sclerosis clinic who had undergone MRI with gadolinium along with DWI. The images were evaluated to detect gadolinium enhancing lesions and lesions showing restricted diffusion in DWI. ADC values were measured on Gd+ lesions and all lesions showing restricted diffusion as well as 2 Gd- lesions and 1 area of NAWM in all patients. Comparison of the ADC values of the Gd+, Gd− lesions and NAWM were performed. The predictive value of the restriction on ADC map for enhancement of lesions was also calculated.
DWI values were measured on 275 T2 lesions that included 68 Gd+ lesions and 207 Gd- lesions, as well as 104 corresponding NAWM in each MRI. Thirty four lesions showed restricted diffusion on DWI. The median ADC minimum of enhancing lesions was significantly lower than NAWM and more strongly lower than the non-enhancing lesions. Most DWI restricted lesions showed gadolinium enhancement (specificity ≥94%), but many enhancing lesions did not show visually detectable restriction in DWI (sensitivity ≤ 34%). Most of the enhancing or restricted lesions were not symptomatic, but the median ADC minimum of symptomatic lesions was lower than asymptomatic lesions.
Enhancing lesions show heterogeneity in ADC metrics. ADC values of enhancing lesions have lower ADC minimum comparing to non-enhancing lesions. ADC values are slightly lower in symptomatic lesions, but this correlation is not strong enough to be used as a predictive marker. Visual appreciation of restricted lesions on ADC map has poor correlation with gadolinium enhancement of lesions and is a poor screening for this purpose. However, DWI restriction, if present, is a strong predictor of Gd enhancement.