Stroke is one of the most time-sensitive medical emergencies. The treatments that produce the best outcomes (clot-busting drugs and mechanical clot retrieval) work only within defined time windows, and those windows are measured in hours. The clinical task of recognizing a stroke when a patient first presents is therefore unusually consequential: a delay of an hour can be the difference between full recovery and lifelong disability. The medical literature estimates that roughly 9% of strokes are initially misdiagnosed in the emergency setting. When a misdiagnosis costs a patient the chance to receive timely treatment, the consequences are often severe and sometimes permanent.
This guide covers what stroke is, why it is sometimes missed, how it is diagnosed and treated in Ontario, and how stroke malpractice claims are structured and proven. It is written for patients and families who suspect that a delayed or missed diagnosis has caused harm, and for anyone trying to understand whether the clinical care during an acute stroke event met the standard of care.
What a stroke is
A stroke occurs when blood flow to part of the brain is interrupted, causing brain cells in the affected area to die. The location and extent of the affected tissue determine the symptoms and the long-term consequences. Strokes are broadly classified as ischemic, hemorrhagic, or transient ischemic attack (TIA), with a smaller number caused by other conditions such as tumours, infections, or congenital vascular abnormalities.
Ischemic stroke is caused by a blockage of an artery supplying the brain, most commonly by a clot that has either formed in the artery or travelled there from elsewhere in the circulation. Roughly 85% of strokes are ischemic.
Hemorrhagic stroke is caused by bleeding in or around the brain, typically from a ruptured artery. The bleeding both deprives downstream brain tissue of blood flow and causes additional damage by exerting pressure on surrounding structures. High blood pressure is the most common contributing factor; aneurysms and arteriovenous malformations are other recognized causes.
Transient ischemic attack (TIA) is, in clinical terms, a brief blockage that resolves before causing permanent injury. The traditional definition required symptoms to resolve within 24 hours, though most TIAs resolve much faster. The current clinical view treats TIA and minor ischemic stroke as points along a single spectrum. A TIA is an important warning event: a person who has experienced a TIA is at substantially elevated risk of a full stroke, often within days.
The distinction between ischemic and hemorrhagic stroke is critical clinically because the treatments are opposite in direction. Ischemic stroke is treated by restoring blood flow, often using clot-dissolving drugs. Hemorrhagic stroke requires controlling the bleeding and, in some cases, surgical intervention. Giving a clot-dissolving drug to a person with an undiagnosed hemorrhagic stroke can be catastrophic. Distinguishing the two is therefore an early and essential step in the workup of any suspected stroke.
Recognizing a stroke
The most widely promoted public-education tool for recognizing stroke in Canada is the FAST mnemonic developed by the Heart and Stroke Foundation of Canada:
- Face: is one side of the face drooping?
- Arms: does one arm drift down when both are raised?
- Speech: is the person’s speech slurred or jumbled?
- Time: time to call 9-1-1 immediately
FAST captures the three most common signs of a left-side or right-side hemispheric stroke (the strokes that affect the largest volume of brain tissue and produce the most recognizable symptoms). These are the strokes that are most reliably identified by both bystanders and clinicians.
Strokes that affect the posterior circulation (the brain stem, cerebellum, and back of the brain) produce different symptoms: dizziness, nausea, vertigo, balance problems, double vision, difficulty swallowing. These symptoms overlap with much more common conditions (inner ear problems, viral illnesses, migraine), and posterior circulation strokes are among the most frequently missed in emergency departments. A patient with an acute presentation of dizziness and nausea is far more often suffering from something benign than from a stroke, and the clinical challenge is to avoid missing the small minority who are not.
Other less specific stroke symptoms include sudden severe headache (sometimes described as “the worst headache of my life,” classically associated with subarachnoid hemorrhage), sudden vision changes in one or both eyes, and sudden onset of confusion or difficulty understanding speech.
Why some strokes are missed
The medical literature has identified several patterns that increase the risk of misdiagnosis:
Younger patients. Stroke is often perceived as a disease of the elderly, and clinicians may anchor on alternative explanations (migraine, intoxication, psychiatric presentation) when the patient is in their twenties, thirties, or forties. Stroke in young patients is less common but not rare, and the consequences of missing it are particularly severe given the patient’s life expectancy.
Women. Women presenting with stroke are more likely than men to present with non-classical symptoms (fatigue, mental status change, generalized weakness) rather than the focal symptoms captured by the FAST mnemonic. Studies have repeatedly found that women experience longer pre-hospital and in-hospital delays in stroke diagnosis.
Posterior circulation strokes. As noted above, these strokes produce non-specific symptoms (dizziness, nausea, balance problems) that overlap with much more common benign conditions.
Transient or fluctuating symptoms. Patients whose symptoms have improved by the time they reach the emergency department, or whose symptoms come and go, can be falsely reassured.
Patients with pre-existing conditions. Patients with known migraine, multiple sclerosis, or psychiatric history may have new symptoms attributed to their existing condition rather than recognized as a new stroke.
These patterns are not, by themselves, evidence of negligence. Many patients in these categories are correctly diagnosed. But they are categories where vigilance is warranted, and where a pattern of missed diagnoses across multiple cases can reflect institutional or systemic problems rather than individual error.
How stroke is diagnosed
The work-up for a suspected stroke proceeds in parallel rather than in sequence: imaging, bloodwork, and neurological examination happen simultaneously to compress the time to diagnosis. The components include:
- Neurological examination. A detailed assessment of cranial nerve function, motor function, sensory function, coordination, speech, and cognition. Standardized scoring systems such as the National Institutes of Health Stroke Scale (NIHSS) are used to quantify the severity of the deficit.
- CT scan of the brain. A non-contrast CT is the first-line imaging test in most stroke protocols. It can identify hemorrhagic stroke quickly, which is the immediate clinical priority before considering clot-dissolving treatment, and can identify some ischemic strokes, though early ischemic changes on CT can be subtle. CT angiography (CT with contrast) can identify large vessel occlusions that are candidates for endovascular treatment.
- MRI. More sensitive than CT for identifying ischemic stroke, particularly small or posterior circulation strokes. MRI is not always immediately available, and the priority in the hyperacute setting is usually to begin CT-based assessment first.
- Bloodwork. Coagulation status, blood glucose (severe hypoglycemia can mimic stroke), and other parameters relevant to treatment decisions.
- Cardiac investigations. Electrocardiogram and, in many cases, echocardiogram, to identify cardiac sources of clot, particularly atrial fibrillation.
- Carotid imaging. Ultrasound or CT/MR angiography of the carotid arteries to identify carotid stenosis as a cause and to guide secondary prevention.
The work-up is extensive, but the components most relevant to immediate treatment decisions (CT of the brain, glucose, neurological examination) are typically completed within minutes of arrival in a well-organized stroke pathway.
How stroke is treated
For ischemic stroke, time is brain. The treatments that produce the best outcomes are most effective when given as soon as possible after symptom onset.
Intravenous thrombolysis uses tissue plasminogen activator (tPA, also called alteplase, or its newer equivalent tenecteplase) to dissolve the clot causing the stroke. The traditional treatment window is up to 4.5 hours from symptom onset, with the benefit greatest in the first 90 minutes and declining steadily thereafter. Some patients are eligible beyond 4.5 hours based on imaging criteria, but the general clinical principle is that earlier is better.
Endovascular thrombectomy (EVT) is a procedure in which a catheter is threaded through the arterial system to the site of the clot in the brain, and a mechanical device is used to remove the clot directly. EVT was established as standard of care in 2015 for patients with large vessel occlusions presenting within six hours of symptom onset. The window has since expanded, and selected patients with favourable imaging are now eligible for EVT up to 24 hours from symptom onset. EVT requires both a stroke centre with the procedural capability and a patient who meets the imaging-based eligibility criteria, so not every ischemic stroke patient is a candidate.
The two treatments are complementary: a patient who receives thrombolysis can still go on to receive EVT if a large vessel occlusion is identified.
For hemorrhagic stroke, treatment focuses on controlling the bleeding and reducing pressure on the brain. Options include reversal of any anticoagulant medications the patient was taking, blood pressure control, and in some cases surgery to remove blood and relieve pressure or to repair the source of the bleeding (an aneurysm, arteriovenous malformation, or other vascular abnormality).
Where stroke negligence claims arise
In my practice, the patterns that produce stroke negligence claims fall into four broad categories.
Misdiagnosis at the first point of contact. A patient with stroke symptoms presents to an emergency department, walk-in clinic, or family doctor. The physician attributes the symptoms to a benign cause and discharges the patient. The stroke is not identified until later, when the treatment window has passed or has narrowed substantially. The legal question is whether a reasonable physician with the same information would have recognized the stroke and initiated the stroke workup.
Failure to investigate adequately. The physician suspects stroke but does not order the imaging or other investigations that would confirm or rule it out, or orders only some of the indicated tests. The patient is reassured and discharged on the basis of an incomplete work-up. The issue is whether the standard of care required the additional investigations.
Failure to interpret imaging properly. The imaging is performed but is misread. A bleed is missed; an early ischemic change is overlooked; a large vessel occlusion is not identified. The treatment that should have followed does not. The issue is whether a reasonable radiologist or treating physician would have identified what was missed.
Delay in initiating treatment after diagnosis. The diagnosis is made, but treatment is not initiated within the relevant time window. The delay can occur at any point in the chain: ordering, mixing, administering, transferring to a centre with EVT capability. Where the delay is unreasonable on the facts and produces a worse outcome, it can support a negligence claim.
Hospitals can also be liable, separately from physicians, where the institutional resources required to deliver timely stroke care were not in place. Staffing, timely access to CT and MRI imaging, the availability of operating room and interventional radiology resources for endovascular treatment, and adherence to provincial stroke care pathways are all institutional responsibilities. Where a hospital has held itself out as providing stroke care but has not in fact resourced that care to the standards expected of a stroke centre, institutional liability can attach.
Stroke care infrastructure in Ontario
Stroke care in Ontario is organized through the Ontario Stroke System, now operating under Ontario Health (CorHealth Ontario). The system is structured around regional stroke centres (which provide the full range of acute and prevention services, including EVT in most cases), enhanced district stroke centres, and district stroke centres, with formal pathways for transferring patients between sites where required. Not all hospitals provide stroke care, and not all that do are equipped for endovascular treatment.
For families investigating whether the care provided in a particular case met the relevant standards, the question is not just what the local hospital did, but what the relevant pathways and protocols required, and whether transfer to a higher-level centre was indicated and either occurred or did not occur in a timely way.
Proving a stroke malpractice claim
A stroke malpractice claim, like any medical malpractice claim, requires proof of three elements: that the standard of care was breached, that the breach caused the injury, and that the injury produced compensable damages.
Standard of care. Whether the conduct of the physician (or hospital staff) fell below the standard expected of a reasonably competent practitioner in the relevant role and circumstances. In stroke cases, this typically requires expert evidence from a stroke neurologist, often supplemented by an emergency medicine specialist, a neuroradiologist, or an interventional radiologist depending on the issues.
Causation. Whether the breach caused the patient’s injury (or worsened it). This is where stroke cases are often won or lost. The challenge is that stroke causes brain injury directly, regardless of the medical response, and the question is whether timely treatment would have made a meaningful difference. The expert evidence has to address what would likely have happened with timely treatment and how that compares to what actually happened. The Ontario decision in Johnson v Lakeridge Health is a useful illustration: even where the standard-of-care analysis was at issue, the trial judge found that the patient’s outcome would not have been altered by earlier diagnosis. Causation analysis in stroke claims requires careful attention to the patient’s specific presentation, the imaging findings, and the realistic probability that any specific intervention would have changed the trajectory.
Damages. The compensable harm caused by the negligence. In stroke cases, the damages calculation often turns on parsing what disability is attributable to the stroke itself (which would have occurred regardless of the medical response) and what additional disability is attributable to the delay or other negligence. This too is expert-driven, typically requiring a stroke neurologist and often a physiatrist or rehabilitation specialist to assess the additional disability and the costs associated with it: additional rehabilitation, attendant care, lost income, future care costs.
The case-by-case nature of stroke claims, and the technical demands of the expert evidence, mean that not every patient with a bad outcome after stroke care has a viable claim. But where the negligence is established and the causation evidence supports a meaningful contribution to the patient’s disability, the damages can be substantial because the consequences of stroke are themselves substantial.
Why this matters
For patients. If you or a family member experienced what you believe was a delayed or missed stroke diagnosis, the timeline matters in two ways. Clinically, the time-sensitive nature of stroke treatment means that delay produces worse outcomes; the same fact, in the legal context, is the basis for the causation analysis. Preserve as much information as you can about the timing of symptom onset, the time of presentation to the hospital, the time of any imaging, and the time of treatment. Get the medical records as soon as practical. The two-year limitation period for medical malpractice claims runs from when you knew or ought to have known the relevant facts, which can be earlier than you might expect. For more on the timing and viability of malpractice claims generally, see Suing for Medical Malpractice in Ontario: What You Need to Know and Can I Sue for Medical Malpractice?
For physicians. The patterns that produce stroke negligence claims (younger patients, women, posterior circulation, fluctuating symptoms, patients with pre-existing conditions) are well documented in the literature. Maintaining a high index of suspicion for stroke in these populations, and following established stroke pathways for the workup, is the most reliable protection against both patient harm and litigation.
For lawyers screening stroke claims. Causation is usually the harder part of a stroke claim than standard of care. The expert evidence must address what timely treatment would likely have done, with concrete reference to the patient’s presentation and the probability that a specific intervention (thrombolysis, EVT, or both) would have been indicated and effective. A claim that depends on speculation about a counterfactual treatment course is one in which causation will be a serious obstacle.
For a discussion of stroke as one of the most dangerous diagnoses missed in Ontario emergency rooms, see Five Dangerous Diagnoses Missed in Ontario Emergency Rooms. For an overview of how ER delay claims more generally are evaluated, see ER Delay Lawyer Toronto. For the broader landscape of complaints and reviews available to Ontario patients, see A Patient’s Guide to Making Complaints About Health Care in Ontario.
