title: Correlation of multiple sclerosis (MS) incidence trends with solar and geomagnetic indices: Time to revise the method of reporting MS epidemiological data.
abstract: BACKGROUND
  Recently, we introduced solar related geomagnetic disturbances (GMD) as a potential environmental risk factor for multiple sclerosis (MS). The aim of this study was to test probable correlation between solar activities and GMD with long-term variations of MS incidence.
  
  
  METHODS
  After a systematic review, we studied the association betwee n alterations in the solar wind velocity (VSW) and planetary A index (AP, a GMD index) with MS incidence in Tehran and western Greece, during the 23(rd) solar cycle (1996-2008), by an ecological-correlational study.
  
  
  RESULTS
  We found moderate to strong correlations among MS incidence of Tehran with VSW (rS = 0.665, P = 0.013), with 1 year delay, and also with AP (rS = 0.864, P = 0.001) with 2 year delay. There were very strong correlations among MS incidence data of Greece with VSW (r = 0.906, P < 0.001) and with AP (r = 0.844, P = 0.001), both with 1 year lag.
  
  
  CONCLUSIONS
  It is the first time that a hypothesis has introduced an environmental factor that may describe MS incidence alterations; however, it should be reminded that correlation does not mean necessarily the existence of a causal relationship. Important message of these findings for researchers is to provide MS incidence reports with higher resolution for consecutive years, based on the time of disease onset and relapses, not just the time of diagnosis. Then, it would be possible to further investigate the validity of GMD hypothesis or any other probable environmental risk factors.
authors.affiliation: Department of Internal Medicine, School of Medicine, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
authors.forename: Fahimeh
authors.initials: F
authors.lastname: Abdollahi
authors.affiliation: Department of Neurology, School of Medicine, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
authors.forename: Seyed Aidin
authors.initials: SA
authors.lastname: Sajedi
keywords: Environmental Risk Factor; Geomagnetic Disturbance; Incidence; Multiple Sclerosis; Solar Wind Velocity