Ambient Pollutants and Spontaneous Intracerebral Hemorrhage in Greater Boston

Background and Purpose- Associations between exposures to ambient air pollution and spontaneous intracerebral hemorrhage (ICH) have been inconsistent, and data on stroke subtypes are currently limited. Methods- We obtained information on all cases of deep or lobar hematomas from ICH patients who were admitted to the Massachusetts General Hospital in Boston, MA, between 2006 and 2011. We linked the date of admission with 1- to 7-day moving averages of fine particulate matter (PM_2.5), black carbon, nitrogen dioxide, and ozone from area monitors. We conducted time-stratified bidirectional case-crossover analyses to assess associations between pollutants and stroke. We also investigated whether associations differed by hemorrhage location and type. Results- There were 577 cases of ICH (295 deep, 282 lobar). Overall, there was no evidence of elevated ICH risk after increases in PM_2.5, black carbon, or nitrogen dioxide in the whole population. However, there was suggestion of heightened risk with higher levels of ozone for averages longer than 1 day although CIs were wide. In models stratified by ICH location, associations with ozone remained positive for patients with lobar (3-day moving average odds ratio, 1.62; 95% CI, 1.18-2.22) but not deep ICH (odds ratio, 0.88; 95% CI, 0.65-1.20). Larger estimates were observed among participants with a probable diagnosis of cerebral amyloid angiopathy (odds ratio, 2.23; 95% CI, 1.25-3.96). Conclusions- Exposure to ozone may be associated with incidence of lobar ICH, especially among those who have confirmed or probable cerebral amyloid angiopathy.