NEW YORK (Reuters Health) May 18 - Cerebral microbleeds increase the risk of intracerebral hemorrhage (ICH) in patients taking warfarin, a new study suggests.
"These results have potentially worrying
implications for warfarin users with microbleeds in particular," lead
investigator Dr. Caroline E. Lovelock of John Radcliffe Hospital,
Oxford, UK, told Reuters Health by e-mail.
But the results "do not allow us to make definite
statements about whether or not patients with microbleeds should start
warfarin," she added. "Many patients starting warfarin do so because
they are at high risk of having a cardioembolic stroke, and this risk
might still outweigh the risk of hemorrhage even in the presence of
In a systematic review of published and
unpublished data, Dr. Lovelock and colleagues analyzed rates of
microbleeds associated with ICH, stroke, and transient ischemic attacks
(TIA), with results stratified by whether or not patients used
antithrombotics. They also assessed prospective data to determine the
risk of ICH in antithrombotic users with microbleeds.
The pooled data set included 1461 patients with ICH and 3817 with stroke or TIA.
In the June issue of Stroke, the researchers
report that microbleeds were more frequent in warfarin users with ICH
compared to nonusers (odds ratio, 2.7; p < 0.001). There was no
excess of microbleeds in warfarin users versus non-users with
The authors saw a similar but weaker association
in patients taking antiplatelet agents. Microbleeds were more frequent
in antiplatelet users versus non-users with ICH (OR, 1.7; p < 0.001),
but there was no excess of microbleeds with use of the drugs by
patients with stroke or TIA.
In all treatment groups, microbleeds were more
frequent in ICH versus stroke/TIA patients. The difference was greater
among warfarin and antiplatelet users (ORs, 8.0 and 5.7, respectively)
compared to nonantithrombotic users (OR, 2.8; p difference between
pooled OR, 0.01).
The pooled prospective data set included 768
patients with stroke or TIA, with a mean follow-up of 27.7 months.
Overall, baseline microbleeds significantly increased the risk of a
recurrent ICH among all antithrombotic users (OR, 12.1; p < 0.001).
Among warfarin users, microbleeds did not significantly increase the
risk of recurrent ICH -- but there were only 5 such cases in warfarin
"We need tighter estimates of the risks of
intracerebral hemorrhage on warfarin in people with microbleeds, and in
particular we need to know what the risks are for patients with just one
or two microbleeds versus many microbleeds," Dr. Lovelock said.
Even after pooling results of published and
unpublished cohorts of patients, there are still very few data on
warfarin users, and "more prospective studies of patients with
microbleeds are therefore urgently required," Dr. Lovelock said.
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