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Claimant in stroke case fails to prove causation on the balance of probabilities.

Articles | Fri 22nd Feb, 2019

Sophie Mortimer successfully represented the Defendant in a clinical negligence claim concerning whether a stroke would have been prevented, or its effects ameliorated, with the provision of:

  1. Aspirin within 24 hours of a transient ischaemic attack (“TIA”); or
  2. Timely thrombolysis.

The judge held that, even though there were gaps in the medical literature, the Claimant had to prove his case on the balance of probabilities. He was unable to discharge the burden of doing so.


On the morning of 18 July 2011, the Claimant suffered a TIA. He attended hospital shortly after. The Defendant admitted that he should have been seen by a stroke nurse, referred to the next morning’s TIA clinic and admitted and kept under observation. It was also admitted that he should have been prescribed 300mg of aspirin. Instead, the doctor who reviewed the Claimant suspected a TIA but discharged the Claimant home at 16:20.

The Claimant stayed at home on 19 July. When his wife arrived home at 15:00 it was obvious he had had a stroke. An ambulance was called. The Claimant arrived at hospital at 16:11 and thrombolysis was started at 18:00.

While breach of duty had been admitted, causation was in issue.

The efficacy of aspirin

The judge (HHJ Baucher), found that the Claimant should have received 300mg of aspirin by 15:12 on 18 July. It was the Claimant’s case that, on the balance of probabilities, aspirin more than halves the risk of recurrent ischaemic stroke after TIA by 24 hours after the first event. An important issue was whether a 2016 meta-analysis (“the Rothwell Paper”) supported efficacy of aspirin within a 24 hour period.

The judge did not find the Defendant’s expert’s evidence on this issue to be of any material assistance, on the basis that he had to accept that he had misunderstood parts of the Rothwell paper.

Under cross examination, the Claimant’s expert accepted that he was not saying that there was evidence of aspirin’s efficacy within 24 hours based on the Rothwell paper. He based his opinion on his email correspondence with Professor Rothwell and a different paper which did suggest aspirin is effective within 12-24 hours. However, he ultimately conceded that he could not state that on the balance of probabilities aspirin is effective in less than 24 hours.

The judge considered that she could attach only limited weight to the email correspondence, particularly given Professor Rothwell’s stated desire not to be involved in medico-legal proceedings. After a detailed consideration of the literature, the judge was satisfied that the evidence was not such as to establish, on the balance of probabilities, that aspirin would have prevented the stroke on 19 July. The literature showed some benefit in the first 24 hours, but that was not sufficient to discharge the burden.

The Claimant conceded that it was necessary to prove causation on the balance of probabilities and that this was not a material contribution case. It was not sufficient for the Claimant to show a reduction in risk. The judge added that, while there might be gaps in the medical literature in relation to the efficacy of aspirin in the first 24 hours, they were not such that she could not make findings on the balance of probabilities. The modified causation test in Bailey v MOD[2008] EWCA Civ 883 did not, therefore, apply.


The Claimant’s case was that timely thrombolysis would have resulted in a significantly better outcome.

The Defendant conceded that, but for the Defendant’s breach of duty, the stroke would have occurred while the Claimant was an inpatient. The judge found that in such circumstances, thrombolysis would have commenced no earlier than one hour after the stroke’s onset.

Both the mechanism of the stroke and the National Institutes of Health Stroke Scale (“NIHSS”) score were relevant to whether thrombolysis within an hour would have made a difference.

The judge therefore had to decide whether the stroke was caused by one or more large clots causing immediate near complete occlusion of the artery, or by a progressive mechanism. She emphasised that, although she had been unable to rely on the Defendant’s expert in relation to the aspirin issue, this did not taint his evidence as a whole. In fact on this issue she preferred his evidence and found that the stroke was caused by a clot which formed in the proximal middle cerebral artery (“MCA”) and stayed there (i.e. not by a progressive mechanism).

The judge found that the stroke occurred by 14:00. On admission, the Claimant’s NIHSS score was 20, on a scale of 0-42 where a score of 16-21 indicates moderate to severe stroke. The judge (applying Keefe v The Isle of Man Steam Packet Company Ltd [2010] EWCA Civ 683) recognised that owing to the Defendant’s negligence she had no recorded NIHSS score for the time when the Claimant should have been in hospital and that therefore she should judge the Claimant’s evidence benevolently and the Defendant’s evidence critically. Nonetheless, she was satisfied that this was not a stroke in evolution and based on the Defendant’s expert’s interpretation of the ambulance records she found that the Claimant had already reached a score of 20 at 15:29.

On review of the literature, and on the basis that the experts agreed that overall thrombolysis is only beneficial in about one third of patients, with those with proximal MCA clots doing less well, the judge was not satisfied on the balance of probabilities that timely thrombolysis within an hour would have made any difference to the outcome.

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