Objective Using positron emission tomography (PET) with [11C]flumazenil ([11C]FMZ), an antagonist of the central benzodiazepine site located within the GABAA receptor, we quantified and mapped neuronal damage in the gray matter (GM) of patients with multiple sclerosis (MS) at distinct disease stages. We investigated the relationship between neuronal damage and white matter (WM) lesions and evaluated the clinical relevance of this neuronal PET metric. Methods A cohort of 18 MS patients (9 progressive and 9 relapsing-remitting) was compared to healthy controls and underwent neurological and cognitive evaluations, high-resolution dynamic [11C]FMZ PET imaging and brain magnetic resonance imaging. [11C]FMZ binding was estimated using the partial saturation protocol providing voxel-wise absolute quantification of GABAA receptor concentration. PET data were evaluated using a region of interest (ROI) approach as well as on a vertex-by-vertex basis. Results [11C]FMZ binding was significantly decreased in the cortical GM of MS patients, compared to controls (–10%). Cortical mapping of benzodiazepine receptor concentration ([11C]FMZ Bmax) revealed significant intergroup differences in the bilateral parietal cortices and right frontal areas. ROI analyses taking into account GM volume changes showed extensive decrease in [11C]FMZ binding in bilateral parietal, cingulate, and insular cortices as well as in the thalami, amygdalae, and hippocampi. These changes were significant in both progressive and relapsing-remitting forms of the disease and correlated with WM T2-weighted lesion load. [11C]FMZ cortical binding correlated with cognitive performance. Interpretation This pilot study showed that PET with [11C]FMZ could be a promising and sensitive quantitative marker to assess and map the neuronal substrate of GM pathology in MS. Ann Neurol 2015;78:554–567
