Stephen Makin, PhD
Anyone who has been to a stroke unit’s imaging meeting will know this situation.
Someone has performed an MRI on their patient with atrial fibrillation, someone who is at high risk of a further stroke, and would usually be started on anticoagulation. Now it shows some microbleeds, and they are considering whether they should still offer anticoagulation.
Someone else will tell you that a meta-analysis of observational studies suggests that CMB is associated with an increased risk of both haemorrahgic and ischaemic stroke.
Someone mutters that maybe the MRI has just caused more trouble, and wonders why you requested it in the first place; after all, we have always managed to diagnose stroke without MRI for decades.
Someone else will say that as none of the trials of anticoagulation required MRI at study entry, so patients with microbleeds must have been included in these studies.
Dr. Shoamanesh and colleagues are in this group. They have taken things a step further and decided that as we know the age of patients in the different studies of the effectiveness of anticoagulation in AF, we can estimate what proportion of them have microbleed, and then estimate the relative risk reduction in that group of patients.
They’ve then taken this estimate to show that the patients who are likely to have the microbleeds are the very ones that are likely to have the most benefit from anticoagulation. However, we don’t know if the patients with microbleeds were the ones who then went on to bleed.
This is an interesting exercise, but it doesn’t really answer the question. We still don’t know whether anticoagulation carries specific harm for patients with microbleeds. We do know that it may benefit them a lot, and if we don’t anticoagulate them, we may be denying a beneficial treatment because of a theoretical risk.