In medical malpractice litigation, an admission of negligence by the defendant physician is the rarest of starting points. The plaintiff is freed from the most contested element of the case and can focus the trial on causation alone. The expectation, intuitively, is that an admitted breach makes a successful claim nearly inevitable.
It does not. Johnson v Lakeridge Health Corporation, 2024 ONCA 291 is a recent reminder that causation in medical malpractice is its own contest. The defendant in Johnson admitted that she had been negligent in discharging the patient without reviewing a critical imaging report. The plaintiffs still lost, because the trial judge was not satisfied that the negligence had caused the harm. The Court of Appeal upheld the dismissal.
The facts
In October 2012, William Johnson was 43 years old. On October 17, he attended at hospital with a fainting episode and was treated and released. He returned the next day, and tests confirmed that he had suffered an ischemic stroke. He was admitted, started on Heparin (an anticoagulant), and the underlying cause of the stroke was identified as a vertebral artery dissection: a tear in the wall of one of the arteries supplying blood to the brain.
On October 23, 2012, Mr. Johnson was discharged by Dr. Rose-Anne Vieira. She prescribed antiplatelet therapy (Aspirin) but, critically, did not review the MRI angiogram report that had identified the dissection. Six days later, on October 29, Mr. Johnson saw his family doctor. The family doctor reviewed the MRA, contacted Mr. Johnson’s neurologist, and Mr. Johnson was sent back to hospital and started on intravenous Heparin.
Less than twenty-four hours later, on October 30, 2012, Mr. Johnson suffered a second, much more severe stroke. He required emergency surgery, intubation, and months of inpatient rehabilitation. He was left with significant ongoing symptoms including vertigo, headaches, speech and vision difficulties, and reduced mobility.
The trial
Damages were agreed. Dr. Vieira admitted that she had been negligent in failing to review the MRA report before discharging Mr. Johnson on October 23. The only issue at trial was causation: would the second stroke have been avoided if Dr. Vieira had read the report and started anticoagulation earlier?
The trial proceeded essentially on the evidence of two experts.
For the plaintiffs, Dr. Louis Caplan, a professor at Harvard Medical School and a globally recognized authority on stroke. He testified that earlier anticoagulation would likely have prevented the second stroke.
For the defence, Dr. David Gladstone, a leading Canadian stroke specialist. He testified that the literature did not support the conclusion that Heparin would have prevented the second stroke. The recurrence rate for stroke in patients with cervical artery dissection treated with Aspirin was, on the evidence, comparable to the recurrence rate for those treated with Heparin: roughly two percent.
The trial judge rejected Dr. Caplan’s evidence as anecdotal and accepted Dr. Gladstone’s. He accepted that, had Dr. Vieira reviewed the MRA, she would have consulted with another physician who would likely have advised against discharge and likely started Mr. Johnson on Heparin. He accepted that Mr. Johnson would have been fully Heparinized by October 30. But he was not satisfied that earlier Heparinization would have prevented the second stroke. The plaintiffs had, on the evidence, not bridged the causal gap.
The action was dismissed: Johnson v Lakeridge Health Corporation, 2023 ONSC 2575.
The Court of Appeal
The plaintiffs appealed. They argued that the trial judge had improperly characterized Dr. Caplan’s evidence as anecdotal and had effectively required them to prove causation to a level approaching scientific certainty rather than the “robust and pragmatic” standard articulated by the Supreme Court of Canada in Snell v Farrell, [1990] 2 SCR 311.
The Court of Appeal dismissed the appeal in Johnson v Lakeridge Health Corporation, 2024 ONCA 291. It saw no palpable or overriding error in the trial judge’s analysis. It did not engage in detail with the plaintiffs’ arguments about the standard for causation or about the trial judge’s treatment of Dr. Caplan’s evidence.
The doctrinal context
In Canadian medical malpractice law, causation must be proven on a balance of probabilities under the “but for” test confirmed in Clements v Clements, 2012 SCC 32. Snell v Farrell held that the analysis is to be applied with robust and pragmatic common sense, not with the rigour of scientific proof. A plaintiff is not required to establish causation through clinical certainty. The trier of fact may draw common-sense inferences from the evidence as a whole.
The application of those principles in any given case turns heavily on the expert evidence. The trial judge’s role is to weigh the experts’ credibility and reasoning, identify the conclusions that follow from the evidence, and apply the legal test to those conclusions. Johnson is a case in which that exercise produced an outcome adverse to the plaintiffs, despite an admission of negligence and despite expert evidence from a globally recognized authority.
The Court of Appeal in Johnson did not provide further guidance on the line between proper rejection of expert opinion as “anecdotal” and improper insistence on scientific certainty in causation analysis. The decision therefore stands as a result rather than as a doctrinal restatement, and the underlying tension between the expert evidence and the medical literature on cervical artery dissection (in which the published recurrence rates were similar across treatment regimens) was decisive.
Why this case matters
For plaintiffs and their counsel. Johnson is a sobering reminder that an admission of negligence does not guarantee a successful outcome. Causation can be the harder element. The case also illustrates the practical risk in expert selection: the world’s foremost authority on a clinical topic is not necessarily the most persuasive expert witness in a particular trial, and the trial judge’s assessment of the experts will often be decisive. Where the literature shows similar outcomes between the treatment given and the treatment that should have been given, the causation analysis will be difficult regardless of how strong the breach case is.
For defence counsel. Johnson confirms that conceding negligence can be a sound strategy in cases where causation is the genuine vulnerability in the plaintiff’s case. The concession narrows the trial to the strongest defence ground and avoids the credibility consequences of contesting an indefensible breach. The case also illustrates that careful selection of an expert who can speak to the relevant body of literature, rather than to clinical experience alone, can be decisive.
For patients and families. A bad outcome after admitted physician error does not necessarily mean a successful malpractice claim. The legal question is whether reasonable care would have produced a different result, on a balance of probabilities. In some cases, including some stroke cases, the answer is no, because the underlying disease process was already in motion in a way that earlier treatment would not have changed. A consultation with an experienced malpractice lawyer, with the records and expert input, is the most reliable way to find out.
For more on the legal process for medical malpractice claims in Ontario, see Suing for Medical Malpractice in Ontario: What You Need to Know. For a related decision in which causation also defeated a clear breach in a surgical context, see Knight v Lawson: A Surgical Injury Where Causation Defeated the Claim. For broader writing on stroke and medical malpractice, see Stroke Misdiagnosis and Medical Malpractice.
Trial Decision: Johnson v Lakeridge Health Corporation, 2023 ONSC 2575 (CanLII) (May 1, 2023, Justice Di Luca)
Appeal Decision: Johnson v Lakeridge Health Corporation, 2024 ONCA 291 (CanLII) (Court of Appeal for Ontario)
Johnson v Lakeridge Health: A Stroke Discharge Where Causation Defeated the Claim
A negligent stroke discharge that failed at causation. The Ontario Court of Appeal upheld the dismissal of the action, despite an admitted breach of standard of care.
In medical malpractice litigation, an admission of negligence by the defendant physician is the rarest of starting points. The plaintiff is freed from the most contested element of the case and can focus the trial on causation alone. The expectation, intuitively, is that an admitted breach makes a successful claim nearly inevitable.
It does not. Johnson v Lakeridge Health Corporation, 2024 ONCA 291 is a recent reminder that causation in medical malpractice is its own contest. The defendant in Johnson admitted that she had been negligent in discharging the patient without reviewing a critical imaging report. The plaintiffs still lost, because the trial judge was not satisfied that the negligence had caused the harm. The Court of Appeal upheld the dismissal.
The facts
In October 2012, William Johnson was 43 years old. On October 17, he attended at hospital with a fainting episode and was treated and released. He returned the next day, and tests confirmed that he had suffered an ischemic stroke. He was admitted, started on Heparin (an anticoagulant), and the underlying cause of the stroke was identified as a vertebral artery dissection: a tear in the wall of one of the arteries supplying blood to the brain.
On October 23, 2012, Mr. Johnson was discharged by Dr. Rose-Anne Vieira. She prescribed antiplatelet therapy (Aspirin) but, critically, did not review the MRI angiogram report that had identified the dissection. Six days later, on October 29, Mr. Johnson saw his family doctor. The family doctor reviewed the MRA, contacted Mr. Johnson’s neurologist, and Mr. Johnson was sent back to hospital and started on intravenous Heparin.
Less than twenty-four hours later, on October 30, 2012, Mr. Johnson suffered a second, much more severe stroke. He required emergency surgery, intubation, and months of inpatient rehabilitation. He was left with significant ongoing symptoms including vertigo, headaches, speech and vision difficulties, and reduced mobility.
The trial
Damages were agreed. Dr. Vieira admitted that she had been negligent in failing to review the MRA report before discharging Mr. Johnson on October 23. The only issue at trial was causation: would the second stroke have been avoided if Dr. Vieira had read the report and started anticoagulation earlier?
The trial proceeded essentially on the evidence of two experts.
For the plaintiffs, Dr. Louis Caplan, a professor at Harvard Medical School and a globally recognized authority on stroke. He testified that earlier anticoagulation would likely have prevented the second stroke.
For the defence, Dr. David Gladstone, a leading Canadian stroke specialist. He testified that the literature did not support the conclusion that Heparin would have prevented the second stroke. The recurrence rate for stroke in patients with cervical artery dissection treated with Aspirin was, on the evidence, comparable to the recurrence rate for those treated with Heparin: roughly two percent.
The trial judge rejected Dr. Caplan’s evidence as anecdotal and accepted Dr. Gladstone’s. He accepted that, had Dr. Vieira reviewed the MRA, she would have consulted with another physician who would likely have advised against discharge and likely started Mr. Johnson on Heparin. He accepted that Mr. Johnson would have been fully Heparinized by October 30. But he was not satisfied that earlier Heparinization would have prevented the second stroke. The plaintiffs had, on the evidence, not bridged the causal gap.
The action was dismissed: Johnson v Lakeridge Health Corporation, 2023 ONSC 2575.
The Court of Appeal
The plaintiffs appealed. They argued that the trial judge had improperly characterized Dr. Caplan’s evidence as anecdotal and had effectively required them to prove causation to a level approaching scientific certainty rather than the “robust and pragmatic” standard articulated by the Supreme Court of Canada in Snell v Farrell, [1990] 2 SCR 311.
The Court of Appeal dismissed the appeal in Johnson v Lakeridge Health Corporation, 2024 ONCA 291. It saw no palpable or overriding error in the trial judge’s analysis. It did not engage in detail with the plaintiffs’ arguments about the standard for causation or about the trial judge’s treatment of Dr. Caplan’s evidence.
The doctrinal context
In Canadian medical malpractice law, causation must be proven on a balance of probabilities under the “but for” test confirmed in Clements v Clements, 2012 SCC 32. Snell v Farrell held that the analysis is to be applied with robust and pragmatic common sense, not with the rigour of scientific proof. A plaintiff is not required to establish causation through clinical certainty. The trier of fact may draw common-sense inferences from the evidence as a whole.
The application of those principles in any given case turns heavily on the expert evidence. The trial judge’s role is to weigh the experts’ credibility and reasoning, identify the conclusions that follow from the evidence, and apply the legal test to those conclusions. Johnson is a case in which that exercise produced an outcome adverse to the plaintiffs, despite an admission of negligence and despite expert evidence from a globally recognized authority.
The Court of Appeal in Johnson did not provide further guidance on the line between proper rejection of expert opinion as “anecdotal” and improper insistence on scientific certainty in causation analysis. The decision therefore stands as a result rather than as a doctrinal restatement, and the underlying tension between the expert evidence and the medical literature on cervical artery dissection (in which the published recurrence rates were similar across treatment regimens) was decisive.
Why this case matters
For plaintiffs and their counsel. Johnson is a sobering reminder that an admission of negligence does not guarantee a successful outcome. Causation can be the harder element. The case also illustrates the practical risk in expert selection: the world’s foremost authority on a clinical topic is not necessarily the most persuasive expert witness in a particular trial, and the trial judge’s assessment of the experts will often be decisive. Where the literature shows similar outcomes between the treatment given and the treatment that should have been given, the causation analysis will be difficult regardless of how strong the breach case is.
For defence counsel. Johnson confirms that conceding negligence can be a sound strategy in cases where causation is the genuine vulnerability in the plaintiff’s case. The concession narrows the trial to the strongest defence ground and avoids the credibility consequences of contesting an indefensible breach. The case also illustrates that careful selection of an expert who can speak to the relevant body of literature, rather than to clinical experience alone, can be decisive.
For patients and families. A bad outcome after admitted physician error does not necessarily mean a successful malpractice claim. The legal question is whether reasonable care would have produced a different result, on a balance of probabilities. In some cases, including some stroke cases, the answer is no, because the underlying disease process was already in motion in a way that earlier treatment would not have changed. A consultation with an experienced malpractice lawyer, with the records and expert input, is the most reliable way to find out.
For more on the legal process for medical malpractice claims in Ontario, see Suing for Medical Malpractice in Ontario: What You Need to Know. For a related decision in which causation also defeated a clear breach in a surgical context, see Knight v Lawson: A Surgical Injury Where Causation Defeated the Claim. For broader writing on stroke and medical malpractice, see Stroke Misdiagnosis and Medical Malpractice.
Trial Decision: Johnson v Lakeridge Health Corporation, 2023 ONSC 2575 (CanLII) (May 1, 2023, Justice Di Luca)
Appeal Decision: Johnson v Lakeridge Health Corporation, 2024 ONCA 291 (CanLII) (Court of Appeal for Ontario)
Paul Cahill
Partner, Davidson Cahill Morrison LLP | LSO Certified Specialist in Civil Litigation
Paul represents victims of medical malpractice across Ontario, with trial experience including a $11.5M jury verdict in a birth injury case. He is recognized in Best Lawyers in Canada and serves as trial counsel to other lawyers on complex medical negligence matters.
About PaulMore on medical malpractice in Ontario.
Other articles by Paul exploring the conditions, decisions, and systems behind preventable medical harm.
Esophageal Intubation in the Emergency Department: A Failed Airway and a Hypoxic Brain Injury
Paul Cahill settled a wrongful death claim involving a misplaced breathing tube and a delayed anesthesiology response in the emergency room.
Noel v Hawrylyshyn: Battery, Informed Consent, and Urgent Operative Delivery
A 17-day birth injury trial. Battery, informed consent, five negligence allegations, and causation all addressed and rejected. A multi-ground defence dismissal.
McLean v. Valadka – Birth Control Stroke Claim Dismissed
On December 1, 2023, the Ontario Superior Court of Justice dismissed a medical malpractice lawsuit brought by a young woman who suffered a stroke after taking birth control medication provided by her family physician who allegedly failed to advise her of the increased risk of stroke associated with that particular brand of birth control pill (Yaz).