Although conventional MRI is sensitive in detecting the lesions of multiple sclerosis, it disclosed neither demyelination nor axon loss itself. Proton magnetic resonance spectroscopy (MRS) is a nuclear magnetic resonance technique which has the potential to detect axon loss non-invasively during life. The normal proton spectrum is dominated by N-acetyl derived groups (NA; the sum of N-acetyl aspartate (NAA) and N-acetylaspartylglutamate).7 The predominant component of the NA peak is NAA, an amino acid of unknown function which has been shown in experimental studies on neonatal rats to be contained almost exclusively within neurons.8 A loss of neurons (cell bodies and axons) would be predicted to cause a persistent reduction in the concentration of NAA. That this is so has been shown in diseases characterised by neuronal loss.9-12 To test the hypothesis that irrecoverable neurological deficit in multiple sclerosis is associated with axon loss, the apparent concentration of NA has been compared in four groups of patients classified as relapsing-remitting, secondary progressive, primary progressive, and benign.
IMPLICATIONS FOR FUTURE STUDIES
The present study has shown a reduction in [NA] from lesions in those subgroups of patients with a greater degree of clinical disability. By contrast, patients with benign multiple sclerosis showed a preservation of NA from lesions and normal appearing white matter indicating a less destructive pathological process in this patient group. Patients with primary progressive multiple sclerosis showed, in addition to a low [NA] from lesions, a reduction of [NA] from normal appearing white matter, perhaps indicating a more diffuse pathological process in this subgroup.
If I am reading it right, this study seems to imply that an MRS gives a better indication of predicting disability than an MRI.