Seasonality of admissions with multiple sclerosis in Scotland

Previous studies have described a seasonal pattern of MS relapse risk. Vitamin D and infectious triggers are two major candidate environmental risk factors proposed to account for this effect. We aimed to assess MS admissions in Scotland for a possible effect of seasonality. Acute admissions with MS were obtained from the Scottish Morbidity Register between 1997 and 2009. We compared the pattern of these to admissions with other diagnoses. We obtained data on 7098 MS and 6 243 690 non-MS acute and day-case admissions. We found a significant difference in acute MS admissions compared with admissions with other diagnoses (P = 0.0015). There was a significant excess of Scottish MS admissions in April and June with nadirs in March and October. Admissions with MS show a significant seasonal variation throughout the year. Further work will be needed to identify candidate environmental factors with certainty.