Proton MR spectroscopy to assess axonal damage in multiple sclerosis and other white matter disorders

Proton MR spectroscopy allows in vivo measurement of N-acetylaspartate in w hite matter, providing a biochemical index of axonal integrity. Several rec ent studies of patients with multiple sclerosis and other white matter diso rders have shown both transient and sustained decreases in N-acetylaspartat e in white matter lesions and in brain regions appearing normal on conventi onal MRI. These data have emphasised that a substantial amount of axonal da mage or loss (presumably secondary to myelin pathology) is consistently pre sent in most of these disorders. Recent post-mortem studies support these r esults. In contrast to changes seen with conventional MR imaging, decreases in N-acetylaspartate have shown a close correlation with changes in neurol ogical status. This suggests that axonal damage may be more relevant than d emyelination for determining chronic functional impairments in primary whit e matter diseases, Thus, serial measurement of brain N-acetylaspartate with proton MR spectroscopy can provide a reliable and clinically-relevant moni tor of disease evolution. As pathological changes responsible for long-term morbidity are logically important targets for therapeutic agents, early tr eatment directed at axonal protection should be useful in these disorders.