A proton magnetic resonance spectroscopy study of the striatum and cerebral cortex in Parkinson's disease

Animal studies have suggested an increased striatal glutamate activity in Parkinson's disease models, although this has not been substantiated in magnetic resonance spectroscopy studies in patients. Our initial aim was to assess glutamate and glutamine levels in the striatum of patients with idiopathic Parkinson's disease, using multivoxel proton magnetic resonance spectroscopy techniques. Since data were collected from other areas of the brain without a priori selection, information on the cortex was also obtained. Twelve healthy volunteers, seven dyskinetic and five non-dyskinetic patients were studied. Peak area ratios of choline-containing compounds (Cho), glutamine and glutamate (Glx) and N-acetyl moieties including N-acetylaspartate (NAx), relative to creatine (Cr) were calculated. Spectra were analysed from the corpus striatum, the occipital cortex and the temporo-parietal cortex. The median Glx/Cr ratio was unaltered in the striatal spectra of Parkinson's disease patients compared to healthy controls. However, the more severely affected patients had significantly reduced NAx/Cr ratios in spectra localised to the temporo-parietal cortex, compared to healthy controls. Furthermore, the entire patient population had significantly reduced Cho/Cr ratios in spectra from the temporo-parietal cortex, compared to the reference population. We found no evidence of increased striatal glutamate in either dyskinetic or non-dyskinetic Parkinson's disease. However, the low NAx/Cr and Cho/Cr ratios in the temporo-parietal cortex may indicate the presence of subclinical cortical dysfunction.