1. Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, WA, USA
2. Multiple Sclerosis Center of Excellence – West, Veterans Administration Puget Sound, Seattle Division, Seattle, WA, USA
3. Department of Epidemiology, University of Washington School of Public Health, Seattle, WA, USA
4. Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, MI, USA
5. Department of Neurology, University of Washington School of Medicine, Seattle, WA, USA