Imaging studies of early MS show axonal injury

Two imaging studies were recently published on early MS (one using early RRMS subjects and the other using people with a clinically isolated syndrome, or CIS). These studies were very similar, using longitudinal 1H-MRS imaging to detect the amount of axonal injury based on the levels of a metabolite called N-acetylaspartate (NAA). NAA is found almost exclusively in neurons and is decreased wherever there is axonal damage. The studies both showed lower levels of NAA in MS subjects compared with controls, but differed in their conclusions about the reversibility of this damage.

In the early RRMS study, 20 RRMS subjects and 10 healthy controls had yearly 1H-MRS exams for two years, and a variety of metabolites serving as markers for different types of cells were measured. The only metabolite that differed in concentration between RRMS and control subjects was NAA, which was decreased at baseline by 7-8% in both the white and gray matter. However, at follow-up, the NAA levels in the RRMS subjects' normal appearing white matter appeared to rebound somewhat. The CIS study included 35 CIS subjects and 12 healthy controls, with scans taken at baseline and after 12 months. The authors of this study measured NAA in the whole brain rather than white and gray matter separately. They also found significantly lower NAA in CIS subjects vs. controls. Unlike the previous study, however, NAA declined in both groups over the follow-up time period with no apparent rebound. This second study also examined whether 1H-MRS could predict which CIS subjects would convert to MS over the follow-up period. 24 of the 35 subjects did convert, but their NAA measurements did not distinguish them from the subjects who did not convert.