Motor neuron diseases: comparison of single-voxel proton MR spectroscopy of the motor cortex with MR imaging of the brain.

PURPOSE: To evaluate single-voxel proton magnetic resonance (MR) spectroscopy in detection of abnormality of the upper motor neuron in patients with motor neuron diseases. MATERIALS AND METHODS: In 43 of 50 patients with motor neuron disease and 14 of 14 control subjects, matching sets of MR spectra were obtained in the left and right motor cortex. The ratio of N-acetylaspartate (NAA) to creatine (Cr) was derived from peak area measurements. Mean ratios were calculated for control subjects and several patient groups, including patients with amyotrophic lateral sclerosis (ALS) or primary lateral sclerosis (PLS). MR images were evaluated for corticospinal tract hyperintensity and central sulcus dilatation. RESULTS: Mean NAA/Cr values were significantly different between control subjects and the ALS or PLS groups (P < .05). With an optimal cutoff of 2.5, NAA/Cr values were abnormal in 15 (79%) of 19 patients with ALS, 12 (67%) of 18 patients with PLS, and one (7%) of 14 control subjects. Corticospinal tract hyperintensity, central sulcus enlargement, or both were found in 43% of the ALS group, 24% of the PLS group, and 7% of the control group. CONCLUSION: NAA/Cr values determined at single-voxel proton MR spectroscopy are more sensitive than are standard findings at MR imaging in the detection of upper motor neuron disease.