1. Multiple Sclerosis Center of Excellence–East, Department of Veterans Affairs (VA), Maryland Health Care System, Baltimore, MD;
2. Multiple Sclerosis Center of Excellence–East, Department of Veterans Affairs (VA), Maryland Health Care System, Baltimore, MD;Department of Neurology, Georgetown University School of Medicine, Washington, DC;
3. Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD;
4. Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA;
5. Robert J. Dole VA Medical Center, Wichita, KS; and Department of Preventive Medicine and Public Health, University of Kansas Medical Center, Wichita, KS;
6. Department of Biostatistics, University of Alabama at Birmingham, Birmingham, AL