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. 2017 Jun;264(6):1059-1067.
doi: 10.1007/s00415-017-8485-0. Epub 2017 Apr 19.

Seasonal variation in multiple sclerosis relapse

Katharine Harding  1   2   3 , Kate Tilling  4 , Claire MacIver  1   3 , Mark Willis  1   2 , Fady Joseph  3 , Gillian Ingram  2   5 , Claire Hirst  2   5 , Mark Wardle  2 , Trevor Pickersgill  2 , Yoav Ben-Shlomo  4 , Neil Robertson  6   7
Affiliations

Seasonal variation in multiple sclerosis relapse

Katharine Harding et al. J Neurol. 2017 Jun.

Abstract

Relapses are a characteristic clinical feature of multiple sclerosis (MS), but an appreciation of factors that cause them remains elusive. In this study, we have examined seasonal variation of relapse in a large population-based MS cohort and correlated observed patterns with age, sex, disease course, and climatic factors. Relapse data were recorded prospectively in 2076 patients between 2005 and 2014. 3902 events were recorded in 1158 patients (range 0-24). There was significant seasonal variation in relapse rates (p < 0.0001) and this was associated with monthly hours of sunshine (odds ratio OR 1.08, p = 0.02). Relapse rates were highest in patients under the age of 30 (OR 1.42, p = 0.0005) and decreased with age. There was no evidence of different relapse rates for males compared to females (OR 0.90, p = 0.19). Identification of potentially modifiable environmental factors associated with temporal variation in relapse rates may allow alteration of risk on a population basis and alteration of outcome of established disease once established. Future epidemiological studies should examine dynamic environmental factors with serial prospective measurements and biological sampling. Significant seasonal differences in relapse rates highlight the importance of environmental factors in disease expression and should be taken into account when planning clinical trials in which relapse frequency is an outcome. In addition, identification of potentially modifiable factors associated with this variation may offer unique opportunities for alteration of risk of relapse and long-term outcome on a population level, and suggest putative biological mechanisms for relapse initiation.

Keywords: Epidemiology; Multiple sclerosis; Relapses; Seasonal.

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Conflict of interest statement

Conflicts of interest

The author(s) declare that they have no competing interests.

Ethical standard statement

The study was approved by the South East Wales Research Ethics Committee (ref 05/WSE03/111).

Informed consent

All patients provided written informed consent.

Figures

Fig. 1
Fig. 1
Line graph showing rate ratios and confidence intervals for MS events in each month, as calculated using Poisson regression
Fig. 2
Fig. 2
Line graph showing relapses per month, grouped by sex (top), age at relapse (middle), and disease course (bottom)
Fig. 3
Fig. 3
Line graph showing relapses per month observed, by recovery from the relapse
See this image and copyright information in PMC

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