THE TRANSVERSE MAGNETIZATION DECAY CHARACTERISTICS OF LONGSTANDING LESIONS AND NORMAL-APPEARING WHITE-MATTER IN MULTIPLE-SCLEROSIS

The characteristics of transverse magnetisation decay of 120 longstand ing lesions and 40 regions of normal-appearing white matter have been analysed in 40 patients with multiple sclerosis (MS) and 10 normal con trols. Fifty lesions showed a biexponential decay in which two water c ompartments one probably intracellular, the other extracellular - coul d be defined. There was a higher frequency of biexponential lesions in patients with a primary progressive course but no significant differe nce between benign and secondary progressive groups. Seventy lesions s howed a monoexponential decay, of which 31 showed a T2 of greater than 200 ms, implying that these lesions were predominantly composed of ex tracellular rather than intracellular water. The results imply that an expanded extracellular space within chronic MS brain lesions is a com mon finding at all levels of disability and disease course. In so far as an expanded extracellular space implies axonal loss, the results su ggest that the latter occurs commonly in longstanding MS lesions. The lack of correlation with disability suggests a limited role for the te chnique in therapeutic monitoring.