Association between antithrombotic drug use before chronic subdural haematoma and outcome after drainage: a systematic review and meta-analysis.

In view of their age and vascular co-morbidities, people are often taking an antithrombotic drug when diagnosed with chronic subdural haematoma (CSDH). It is unclear whether antithrombotic use at CSDH diagnosis, or resumption afterwards, is associated with recurrent CSDH or vaso-occlusive events. We systematically reviewed the literature for studies reporting CSDH recurrence or vaso-occlusive events after drainage of CSDH associated with antithrombotic drug use. We searched Medline 1946-2016 and Embase 1974-2016 inclusive for cohort studies reporting the risk of CSDH recurrence or vaso-occlusive events after CSDH associated with antithrombotic (anticoagulant or antiplatelet) drug use. We meta-analysed outcome data using a random effect model and assessed inconsistency between studies using the I-squared (I 2 ) statistic. We found 20 studies reporting outcome after drainage of CSDH associated with antithrombotic drug use. Before CSDH drainage, 337 (11.5%) of 2941 patients in 12 studies used an anticoagulant drug and 600 (19%) of 3150 patients in 11 studies used an antiplatelet drug. The association between antithrombotic drug use and CSDH recurrence was significant for antiplatelet drug use (relative risk [RR] 1.36, 95% CI 1.05 to 1.75; I 2  = 36.3%), but marginally significant for anticoagulant drug use (RR 1.38 95% CI 1.00-1.91; I 2  = 37.5%). Two studies including 30 patients reported one vaso-occlusive outcome event after CSDH. Antithrombotic drug use at CSDH diagnosis may be associated with post-operative CSDH recurrence. It is unclear whether this is attributable to confounding factors, antithrombotic reversal strategies or antithrombotic drug resumption. Further observational studies and randomised controlled trials of antithrombotic drug resumption are needed.