Protocol title: Role of microglia in the pathogenesis of progressive multiple sclerosis~Rationale of the study: The investigators have demonstrated earlier a statistically significant correlation between TSPO-binding and EDSS in a heterogeneous MS-population comprising both early RRMS and late secondary progressive multiple sclerosis (SPMS) patients. Now the investigators aim to evaluate whether TSPO-imaging correlates to EDSS and other disease progression-related clinical and paraclinical parameters in a homogenous cohort of 40-50-year old MS-patients, who are at risk of progression. The A2A-AR expression in this cohort will also be studied using the A2A-AR-binding radioligand 11C-TMSX. The study cohort will also form the basis for a later follow-up study, which will be performed to evaluate the prognostic value of baseline TSPO-imaging in terms of disease progression. TSPO-imaging could thus be used as an imaging biomarker to help identifying patients to therapeutically prevent progression of MS. At the 5 year time point synaptic density will be evaluated using 11C-UCB-J radioligand and PET imaging.~Study population: The study population will consist of a clinically homogenous group of 25 relapsing remitting multiple sclerosis (RRMS) patients with MS-diagnosis for at least 5 years, age 40-50 years, who may be using any first-line MS therapy. The patients will be recruited from the outpatient clinic of the Division of Clinical Neurosciences of the University Hospital of Turku, Finland. In addition the investigators will image a group of 10 age- and sex-matched healthy control subjects for comparison.~Study Objectives Primary: To evaluate how TSPO-ligand binding in the normal appearing white matter (NAWM) correlates to EDSS.~Secondary: 1) To evaluate how TSPO-ligand binding in the NAWM at baseline correlates to other standard clinical and paraclinical parameters typically associated with disease progression 2) To evaluate how 11C-TMSX-binding (to A2A-AR) correlates to the clinical and paraclinical parameters, and to TSPO-binding. 3) To evaluate how synaptic density evaluated using 11C-UCB-J binding correlates to patients cognitive functions.~Inclusion criteria: RRMS, age 40-50 years, MS-diagnosis for a minimum of five years. Exclusion criteria: Previous or present treatment with immunosuppressive medication or biologicals. Steroid treatment within 30 days of evaluation Evaluation of patients: Baseline brain MRI and PET using 11C-PK11195 and 11C-TMSX with a protocol used in our previous studies. MS functional composite (MSFC), brain atrophy, quantitative diffusion tensor magnetic resonance imaging (DTI-MRI) measures, and neuropsychological status. At 5 years PET using 11C-UCB-J radioligand.~Positron emission tomography (PET) imaging methods: 1) Detection of microglial activation. The investigators shall use the TSPO-ligand 11C-PK11195 to evaluate the level of microglial activation in the NAWM, in normal appearing gray matter (NAGM) and in the periplaque areas. The 11C-PK11195 imaging. 2) A2A-AR detection. The investigators shall investigate the distribution of the A2A-ARs using PET and (11C-TMSX). This will be performed to correlate A2A-AR expression with microglial activation in the central nervous system (CNS) of RRMS patients at risk of converting to SPMS. The 11C-TMSX imaging.3) Evaluation of synaptic density using 11C-UCB-J-PET. The association between 11C-UCB-J binding and cognitive functions will be evaluated.~Based on earlier experience with PET ligands it is estimated that 15 subjects per group is enough to reveal 15% difference in 11C-PK11195 and 11C-TMSX uptake between the study groups with 90% power at p-level <0.05. The correlation analyses between the variables will be performed with Spearman's non-parametric test for non-linear, and Pearson's test for linear association.~Facilities: Turku PET Centre (TPC) is the national PET Centre in Finland. It has six state-of the-art PET scanners and a long history of performing PET scanning in neurological disorders, and in animal models thereof (www.turkupetcentre.fi). Radiochemical synthesis of 11C-PK11195 has been established in TPC and study projects on MS patients have been completed and published by our research group previously. The 11C-TMSX and 11C-UCB-J are already in use in the TPC.~People involved: Dr. Laura Airas, MD, PhD. Consultant in neurology, and assistant professor in neurology. Professor Juha Rinne, MD, Consultant in Neurology. Turku PET Centre. Professor Riitta Parkkola, MD, Neuroradiologist. Dr. Eero Rissanen MD, PhD. Dr. Marcus Sucksdorff, MD, PhD student.
Our aim is to evaluate whether translocator binding protein (TSPO)-imaging correlates to Expanded Disability Status Scale (EDSS) and other disease progression-related clinical and paraclinical parameters in a homogenous cohort of 40-50-year old MS-patients, who are at risk of progression. The A2A-AR expression in this cohort will also be studied using the adenosine A2A-receptor (A2A-AR)-binding radioligand 11C-TMSX. The study cohort will also form the basis for a later follow-up study, which will be performed to evaluate the prognostic value of baseline TSPO-imaging in terms of disease progression. TSPO-imaging could thus be used as an imaging biomarker to help identifying patients to therapeutically prevent progression of MS. At the 5 year time point synaptic density will be evaluated using 11C-UCB-J radioligand and PET imaging.