1. Department of Neurology, the Third People's Hospital of Chengdu, the Affiliated Hospital of Southwest Jiaotong University, Chengdu, P.R. China.
2. Department of Neurology, Nanchong Central Hospital, Southwest Medical University, Nanchong, P.R. China.
3. Department of Neurology, Yanting County People's Hospital, Yanting, P.R. China.
4. Institute of Rheumatology and Immunology, Affiliated Hospital of North Sichuan Medical College, Nanchong, P.R. China.
5. Department of Neurology, Chengdu Hospital of the Chinese People's Armed Police Forces, Chengdu, P.R. China.
6. Department of Epidemiology and Statistics, School of Public Health, Kunming Medical University, Kunming, P.R. China.