1. Research Unit of Clinical Medicine , Neurology, , Oulu , Finland
2. University of Oulu , Neurology, , Oulu , Finland
3. MRC, Oulu University Hospital , Oulu , Finland
4. Neurocenter , Neurology, , Oulu , Finland
5. Oulu University Hospital , Neurology, , Oulu , Finland
6. Work Ability and Working Careers Unit, Finnish Institute of Occupational Health , Helsinki , Finland
7. Neurocenter , Neurology, , Kuopio , Finland
8. Kuopio University Hospital , Neurology, , Kuopio , Finland
9. Unit of Neurology , Institute of Clinical Medicine, , Kuopio , Finland
10. University of Eastern Finland , Institute of Clinical Medicine, , Kuopio , Finland
11. Department of Geriatrics, Helsinki University Hospital , Helsinki , Finland
12. Clinical Neurosciences, University of Helsinki , Helsinki , Finland
13. Clinical Neurophysiology and Clinical Neurosciences , HUS Diagnostic Center, , Helsinki , Finland
14. University of Helsinki and Helsinki University Hospital , HUS Diagnostic Center, , Helsinki , Finland
15. Institute for Molecular Medicine Finland, University of Helsinki , Helsinki , Finland