Proton magnetic resonance spectroscopy of the primary motor cortex in patients with motor neuron disease: subgroup analysis and follow-up measurements

Abstract

Objectives: To determine the motor cortex degeneration in patients with amyotrophic lateral sclerosis (ALS) using proton magnetic resonance spectroscopy, and to prove that proton magnetic resonance spectroscopy is suited to monitor the course of disease with follow-up examinations.

Materials and methods: We studied 33 patients with ALS whose conditions were diagnosed according to the El Escorial World Federation of Neurology criteria. Nine patients with ALS were followed up for up to 2 years. The control group included 20 healthy volunteers and 4 patients with multifocal motor neuropathy. Proton magnetic resonance spectroscopy determined levels of the brain metabolites N-acetylaspartate (NAA), choline, inositol-containing compounds, glutamate/glutamine, and phosphocreatine.

Results: Patients with ALS showed a significant reduction in the NAA-choline (P <.001) and NAA-phosphocreatine (P <.005) metabolite ratios and significantly elevated choline-phosphocreatine (P <.005) ratios compared with controls. Inositol-phosphocreatine ratios were also elevated in case patients, but the increase was less pronounced (P <.05). No differences in glutamate/glutamine-phosphocreatine ratios were detected between case patients and controls. An analysis of subgroups demonstrated less significant differences in NAA-choline metabolite ratios (P<.05), even in patients with pure lower motor neuron syndrome (suspected ALS). No changes in metabolite T1 and T2 relaxation times were observed. Patients with multifocal motor neuropathy showed normal metabolic ratios. Progressive alterations in affected metabolite ratios could be documented in the follow-up examinations.

Conclusions: Spectroscopic changes in the motor cortices of patients with ALS correspond with a reduction in levels of NAA and an elevation in levels of choline and inositol compounds. Since NAA is exclusively expressed in neurons, the observed decrease of NAA reflects neuronal loss or dysfunction. Inositol and choline are associated with plasma membrane metabolism, so the release of these compounds may be related to membrane disorders.