Correlation of multiple sclerosis (MS) incidence trends with solar and geomagnetic indices: time to revise the method of reporting MS epidemiological data

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 between alterations in solar wind velocity (Vsw) and planetary A index (Ap, a GMD index) with MS incidence in Tehran and western Greece, during the 23rd 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 one 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 one year lag. Conclusion: 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. Keywords: Correlation analysis, Multiple sclerosis, Incidence, Geomagnetic disturbance, Geomagnetic activity, Solar wind velocity, Environmental risk factor.