[1] Maryland Hlth Care Syst, Multiple Sclerosis Ctr Excellence East, Dept Vet Affairs VA, Baltimore, MD USA
[2] Univ Maryland, Sch Med, Dept Neurol, Baltimore, MD 21201 USA
[3] Georgetown Univ, Sch Med, Dept Neurol, Washington, DC USA
[4] Univ Maryland, Sch Med, Dept Epidemiol & Publ Hlth, Baltimore, MD 21201 USA
[5] Univ Iowa, Dept Internal Med, Carver Coll Med, Iowa City, IA 52242 USA
[6] Robert J Dole VA Med Ctr, Wichita, KS USA
[7] Univ Kansas, Dept Prevent Med & Publ Hlth, Med Ctr, Wichita, KS USA
[8] Univ Alabama Birmingham, Dept Biostat, Birmingham, AL 35294 USA