Biochemical alterations in multiple sclerosis lesions and normal‐appearing white matter detected by in vivo 31P and 1H spectroscopic imaging

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Abstract
The goals of the current study were threefold: first, to confirm previous single volume proton (1H) magnetic resonance spectroscopy results of reduced N‐acetyl aspartate (NAA, a putative marker of neurons) in multiple sclerosis (MS) white matter lesions using multiple volume 1H magnetic resonance spectroscopic imaging (MRSI); second, to measure the phospholipid metabolites phosphomonoesters and phosphodiesters in such lesions using phosphorus (31P) MRSI; and third, to test the hypothesis that biochemical changes occur in the normal‐appearing (on spin echo T2‐weighted magnetic resonance images) white matter in patients with MS. Thirteen subjects with clinically definite MS were studied with both 1H and 31P MRSI, and 19 controls were studied with either 1H MRSI, 31P MRSI, or both. MS lesion, MS normal‐appearing white matter, and region‐matched control spectra from the centrum semiovale were analyzed. The major findings of this study were that in both white matter lesions and normal‐appearing white matter in patients with MS, the metabolite ratio NAA/creatine and the total 31P peak integrals were significantly reduced compared with controls. In addition, in MS lesions NAA/choline and phosphodiesters/total 31P were significantly reduced compared with controls, and in MS normal‐appearing white matter there was a trend for NAA/choline to be reduced compared with controls. In normal‐appearing white matter in patients with MS, total creatine and phosphocreatine were significantly increased compared to controls, as detected with both 1H (total creatine peak integrals) and 31P (phosphocreatine/total 31P) MRSI techniques. These results suggest reduced neuronal density and altered phospholipid metabolites in white matter lesions in patients with MS. Furthermore, the results suggest the presence of biochemical abnormalities not detected by standard spin echo magnetic resonance imaging in normal‐appearing white matter in MS.