Introduction

In a recent mediation, I witnessed a plaintiff’s counsel construct a convincing case for her client having sustained a Mild Traumatic Brain Injury (“mTBI”). The plaintiff had sustained a rear-end collision at high speed, striking his head against the headrest upon impact, followed by successive failed attempts at returning to work, with documented neuropsychological and sleep impairments.

I couldn’t help but think that in less capable hands, this case would have been miscast as routine whiplash injury.

In Ontario right now, garden-variety soft-tissue MVA cases that don’t crystalize into chronic pain usually land in the low five figures for non-pecuniary damages, often gutted by the statutory deductible (indexed to $46,790.05 in 2025, with the deductible disappearing only if the award tops $155,965.54^[1].

By contrast, well-built mTBI/concussion files, with early anchors and coherent functional proof, regularly see $100,000–$250,000 in general damages on judge-alone trials, and they typically clear both the s. 267.5 “serious and permanent” threshold and the monetary threshold that removes the deductible (e.g., Taylor v. Zents, 2024 ONSC 166^[2]: $250,000; Sanson v. Paterson, 2022 ONSC 2972^[3]: $250,000; Graul v. Kansal, 2022 ONSC 1958^[4]: $225,000; Higashi v. Chiarot, 2021 ONSC 8201^[5]: $225,000).

Translation: A well-documented mTBI file can produce materially different outcomes than typical soft-tissue cases, including clearing the threshold and shifting valuation toward income loss and future care.

Mild traumatic brain injury claims do not turn on drama. They turn on disciplined evidence. A persuasive record links a recognizable acute brain event to later functional limitations, supported by contemporaneous documentation and measured expert analysis.

“Mild” describes initial injury severity, not outcome. In practice, the Court wants (and insurers insist on) three things:

1) Proof that an accident produced an acute brain event (e.g. head striking the headrest and MRI);

2) Proof that the plaintiff’s day-to-day function changed in a way that fits that event (e.g. failed return-to-work attempts); and

3) Credible experts who can confirm the diagnosis and rule out common alternative causes.

The Causation Frame

Ontario causation law is stable. The governing test is but-for causation on a balance of probabilities, applied with robust common sense. This is the operative approach in most single-defendant motor cases. Persuasive analyses typically proceed from the accident mechanism through acute clinical indicators to a coherent course of symptoms and function, with authorities such as Snell v. Farrell, 1990 SCR 311^[6] and Clements v. Clements, 2012 SCC^[7].

Pre-existing Conditions: Thin Skull vs. Crumbling Skull

I wrote a blog on this subject recently, “The Thin Skull Meets the Crumbling Skull: Mediation Strategies for Chronic-Pain Litigation”^[8].

Where pre-existing vulnerability or concurrent causes are present, the analysis follows thin-skull and crumbling-skull principles. If fragility increased susceptibility to injury, the individual is taken as found. If a condition was already deteriorating, damages will only compensate the acceleration or aggravation attributable to the accident. That is Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 SCR 458^[9], and is the blueprint for apportionment language that should be in reports and submissions.

Diagnosis and Documentation

mTBI in litigation is generally recognized through event-based criteria and clinical course rather than imaging alone^[10].

In the first 72 hours, anchors include brief loss of consciousness, alteration of mental state (confusion, disorientation, being “dazed”), or post-traumatic amnesia. Early symptoms can include headache, dizziness, photophobia, nausea, irritability, and sleep disruption^[11]

Normal CT/MRI is common and not determinative, as was the case in my recent mediation.

Records that tend to persuade courts are the boring ones such as neurological findings when present, documented return-to-work attempts that fail for reasoned, functional causes; graded exertion intolerance; balance or vision problems, and neuropsychological testing with validity measures explained^[12]. For judicial weighting of functional records, see Graul v. Kansal, 2022 ONSC 1958^[13], where the trial reasons noted functional limitations in daily activities.

Expert Evidence

On expert work, I believe less is more.

A concise expert panel usually proves the most useful. Treating records provide the contemporaneous backbone. A single core medical expert (neurology or physiatry) to synthesize mechanism, acute flags, course, and differential, paired with a careful neuropsychologist who administers and explains validity testing, often suffices.

Vestibular (the plaintiff’s balance system), neuro-ophthalmic, or sleep specialists are most persuasive when the file contains clinical indicators pointing that way. Where validity questions arise, clarity helps. Note which tests raised concerns, re-test with different tools if needed, and account for other explanatory factors like pain, medications, sleep, anxiety, and language.

That candour will save the case. Evasion will not. As Justice Archibald reminds us: face your bad facts head on before the other side does^[14].

Novel Science (and SPECT)

A case cannot be built on novel science.

Ontario trial courts have scrutinized brain SPECT^[15] evidence, sometimes excluding it when proffered as a primary diagnostic tool to prove a TBI^[16], and sometimes admitting it as limited, secondary support for an already-made diagnosis^[17]. Either way, SPECT is a sideshow in most tort files. The plaintiff’s counsel on my recent mediation referred to her client’s SPECT results, but wisely acknowledged their evidentiary limitation. The real case lives in orthodox clinical criteria, functional proof, and validity-sound testing.

If there is an evidentiary north star on novelty and reliability, it is R. v. J.-L.J., 2000 SCC 51^[18] which sets the reliable-foundation test for novel scientific evidence, principles that courts regularly invoke when gatekeeping expert science.

Accident Benefits (Ontario): MIG Battles Are Evidence Battles

Accident Benefits disputes over the Minor Injury Guideline are won and lost on the same fundamentals.

A qualified diagnosis tied to functional impairment, documented over time, rather than labels, is key. The Schedule (O. Reg. 34/10)^[19] still governs the categories and monetary caps. What convinces an insurer to move a claimant out of MIG is not rhetoric but evidence that the injuries are not “predominantly minor,” including a concussion that actually impairs function.

Recent LAT decisions reflect this. Some panels have accepted a family physician’s concussion diagnosis and coherent functional evidence as sufficient to remove a claimant from the MIG, while others have kept claimants within MIG where concussion was not adequately anchored or recovery was rapid and the proof thin.

For example, Gavey v. Wawanesa Insurance, 2024 CanLII 77430 (ON LAT)^[20] accepted a family physician’s concussion diagnosis as adequate to take the matter out of MIG.

By contrast, Castro v. Allstate Insurance, 2023 CanLII 101080 (ON LAT)^[21] is one of a case emphasizing that bare complaints and ambiguous charting won’t do. Tribunals look for coherent medical evidence connecting diagnosis to functional impairment.

Recent bulletins also highlight Ji v. Economical Insurance Company, 2024 CanLII 13083 (ON LAT)^[22] and Vegh v. Unifund Assurance Company, 2024 CanLII 6506 (ON LAT)^[23] both reinforcing that it’s the quality of the medical-functional bridge, not the speciality label, that carries the day.

“Concussion” is not a magic password. Insurers and the LAT will always look at the functional impact.

Building the Record

Ontario Neurotrauma Foundation’s Guideline for Concussion/mTBI & Persistent Symptoms (3rd ed., 2018) is a MUST READ for both plaintiff and defence counsel litigating mTBI^[24].

Files that read coherently usually begin with decisive first-week materials, such as ambulance and emergency records including Glasgow Coma Scale (GCS) and notes on loss of consciousness or amnesia, along with early behavioural observations.

In the first month, a documented follow-up (family physician or concussion clinic), a simple symptom log, and workplace communications or accommodations tend to clarify trajectory for the insurer.

Between months two and six, neuropsychological testing with validity measures is often pivotal, with vestibular or neuro-ophthalmology assessment added where indicated. Insurers will look to return-to-work attempts documented by dates, duties, and reasons for failure as providing concrete functional evidence.

When symptoms persist beyond six months, a differential assessment for migraine, sleep apnea, mood or anxiety disorders, medication effects, and chronic pain may be indicated.

A vocational assessment may also be appropriate where employment loss continues.

Discovery, trial, and language

At discovery and trial, specific contemporaneous detail is generally more persuasive than broad characterization.

Distinctions such as “I don’t know” versus “I don’t remember” can matter, the latter potentially aligning with post-traumatic amnesia. Examination for discovery in mTBI cases commonly focuses on the first 72 hours, return-to-work timelines and duties, and patterns in headache, sleep, sensory intolerance, and driving tolerance. Digital records such as HR emails, productivity metrics, calendars, and time-tracking, can corroborate function.

Submissions that move from mechanism to acute criteria and course of treatment, then invite the Snell robust common-sense synthesis within the Clements but-for framework, tend to match the law’s expectations.

Valuation and mediation reality

On valuation, be clinical, not theatrical.

Adjusters will pay on a file with early anchors, credible return-to-work failure, clean validity data, and a restrained expert panel. They will discount a file with treatment gaps, inconsistent reporting, and a clown car of experts.

Functional evidence carries more weight than descriptive characterization. Documentation showing concrete workplace impact—tasks taking longer, higher error rates, and unsuccessful accommodations—tends to be more persuasive. Without it, self-report inventories alone have limited probative value.

Conclusion

mTBI claims are not settled at mediation (or won in Court) by rhetoric or exotic testing.

They are proved by orthodox causation principles applied to a disciplined record, as I observed recently on a successful mediation. The files that earn confidence from an insurer pair a recognizable acute event with a coherent functional trajectory over time, anchored in contemporaneous notes, measured neuropsychology with validity explained, and a restrained, clinically driven expert panel.

Normal imaging does not end the inquiry. Neither does a label start it. Candid treatment of pre-existing conditions under thin- and crumbling-skull principles completes the picture.

In both tort and SABs contexts, the same lesson holds. Diagnosis matters, but function carries the weight. Where the record documents early anchors, real-world return-to-work experience, and careful differential analysis, courts have the tools to draw robust, common-sense inferences on causation and impairment. Where it does not, even earnest self-report will struggle to persuade.

Evidence matters.

The durable path forward is traditional: admissible facts, tested expertise, and functional truth over time.