Does the extent of axonal loss and demyelination from chronic lesions in multiple sclerosis correlate with the clinical subgroup?

Objective-To determine non-invasively the relation between the degree of ax onal loss and the extent of demyelination in chronic lesions visible on MRI in patients with different subgroups of clinically definite multiple scler osis using H-1 magnetic resonance spectroscopy (H-1 MRS) and magnetisation transfer imaging (MT). Conventional A MRI is unable to differentiate betwee n the various pathological processes occurring in the multiple sclerosis le sion. There are, however, newer MR techniques which show promise in this re spect. Methods- H-1 MRS and MT were performed in 18 patients with clinically defin ite multiple sclerosis who had a wide range of disability and disease durat ion. Results-A significant correlation was found between a reduction in the conc entration of N-acetyl aspartate (NAA; an in vivo marker of axonal loss or d ysfunction) and a reduction in MT ratio (a probable marker of demyelination ) in patients who had entered the secondary progressive stage of the diseas e. Patients with minimal disability after a disease duration of greater tha n 10 years-so called benign multiple sclerosis-showed a relative preservati on of NAA and MT. Conclusions-Because a reduction in MT seems to be a relative marker for dem yelination and a reduction of NAA from chronic lesions is indicative of axo nal loss, this study supports the hypothesis that demyelination and axonal loss occur in the same chronic multiple sclerosis lesions. In addition, the degree of axonal loss and demyelination correlates with clinical heterogen eity.