Fine Particulate Matter Related to Multiple Sclerosis Relapse in Young Patients

Objective: Particulate matter (PM) of aerodynamic diameter smaller than 10 μm (PM(10)) has been associated with multiple sclerosis (MS) relapse. However, the impact of smaller PM with a greater ability to penetrate human organism has never been assessed. We evaluated the impact of PM smaller than 2.5 μm (PM(2.5)) on the risk of MS relapse. Material and Methods: In a case-crossover study, we included 2,109 consecutive hospitalizations likely due to MS relapse in day hospital in 5 MS centers in the Paris area from January 2009 to December 2013. For each hospitalization, the natural logarithm of the average weekly PM(2.5) concentrations (μg/m(3)) at the patient's residence address during each of the 6 weeks (week[0] to week[−5]) preceding admission was compared with the concentration during the previous week, using a conditional logistic regression adjusted on temperature, flu-like syndrome rate, pollen count, and holiday period. Results: PM(2.5) average concentration during week[−3] was significantly associated with the risk of hospitalization for MS relapse [OR = 1.21 (CI 1.01;1.46)]. The association was stronger in patients younger than 30 years [OR=1.77 (CI 1.10; 2.83)]. Conclusion: Our study demonstrates an association between exposure to PM(2.5) and MS relapse, particularly in young people.