A claimant presents with neck pain following a road traffic collision. An employee develops anxiety after a workplace dispute. A patient experiences a poor outcome after treatment. In each case, the diagnosis may be straightforward. The more difficult question is whether the event caused the condition, contributed to it, accelerated it, or simply happened at around the same time.
That distinction sits at the centre of much medico-legal work, yet experts still handle it poorly with surprising frequency.
The temptation is understandable. Clinicians train to diagnose and treat. Solicitors, insurers and claims handlers need something different from the medico-legal expert. They need to know not simply what condition exists, but why it exists and what would have happened had the event under consideration never occurred.
That difference can determine the value of an entire report.
A diagnosis does not answer causation.
One of the most common errors in medico-legal reporting is the assumption that diagnosis answers the causation question. It does not.
Take chronic low back pain. A claimant may report symptoms and meet the relevant diagnostic criteria, but that tells us little about why the symptoms developed. The existence of a condition and the cause of that condition remain separate questions.
The same problem appears in psychological injury claims. A diagnosis of post-traumatic stress disorder does not automatically establish that the index event caused the disorder. The expert must consider the chronology, relevant medical history, pre-existing vulnerability, subsequent events and other plausible explanations before reaching an opinion.
This may sound elementary yet reports still move directly from diagnosis to causation without showing the reasoning in between.
A report might say that a claimant developed symptoms after an accident and then conclude that the accident caused them. That establishes chronology. It does not necessarily establish causation.
Those relying on the report are entitled to expect more.
Few claimants come with a blank medical history.
Pre-existing conditions make causation more difficult.
Few people attending a medico-legal examination have no relevant medical history at all. They may have experienced previous injuries, earlier psychological symptoms, degenerative change or intermittent episodes of pain long before the index event.
The expert should not ignore those factors simply because they complicate the opinion. Their significance needs to be assessed.
One claimant with previously asymptomatic degenerative change may develop symptoms after an accident. Another may have experienced similar symptoms intermittently for several years. A third may already have been progressing towards the same difficulty regardless of the incident.
Those cases require different causation analyses.
In my experience, some reports devote several pages to the claimant’s current symptoms while giving remarkably little attention to what came before them. That approach carries obvious risk. An expert cannot give a dependable causation opinion without considering the claimant’s previous health.
The relevant question is not simply, “What symptoms does the claimant have now?”
It is also, “What was likely to happen anyway?”
The counterfactual is often missing.
The strongest causation opinions usually contain an explicit, or at least clearly recognisable, counterfactual analysis.
What would probably have happened if the accident, treatment, exposure or workplace incident had not occurred?
Experts overlook that question more often than they should.
Without it, the analysis struggles to separate the effects of the event from the natural progression of disease, ageing, pre-existing symptoms or unrelated circumstances.
Consider a claimant with established degenerative spinal change who develops increased symptoms after a collision. The relevant issue may not be whether degeneration exists. It may be whether the collision caused new symptoms, temporarily aggravated existing symptoms, accelerated a deterioration that would otherwise have occurred later, or made no material difference at all.
Those distinctions matter.
The same reasoning applies beyond personal injury work. In clinical negligence cases, the expert may need to consider what outcome would have followed with different treatment. In psychological cases, they may need to assess the course of the claimant’s mental health in the absence of the index event.
Causation therefore requires more than identifying what happened after an incident.
It requires consideration of what would have happened without it.
After does not mean because of.
Chronology can be persuasive. It can also mislead.
Claimants often associate the onset of symptoms with a particular event because that is when they first noticed the problem. Sometimes that association proves clinically convincing. Sometimes the timing is coincidental or only part of the explanation.
Human beings naturally connect events that occur close together in time. Experts are no exception.
The medico-legal expert must resist the temptation to treat temporal association as proof. Instead, the expert should ask whether the proposed relationship makes medical sense and whether the wider evidence supports it.
This becomes particularly important in cases involving chronic pain, psychological injury, neurological symptoms and conditions with several possible contributing factors.
A close temporal relationship may strengthen a causation opinion. It rarely settles the matter on its own.
The reasoning needs to be visible.
Perhaps the most important weakness in some causation opinions is not the conclusion itself but the absence of an explanation.
Experts occasionally reach a perfectly defensible view and then fail to show how they reached it. The reader receives the destination but very little of the route.
That is rarely satisfactory.
A properly reasoned opinion should identify the evidence that influenced the conclusion. It should address relevant competing explanations and explain why the expert considers one explanation more likely than another. Where uncertainty remains, the expert should acknowledge it rather than disguise it with overly confident language.
The reader ought to be able to follow the reasoning even if they disagree with the conclusion.
This is more than a matter of writing style. It affects the weight others may attach to the opinion.
In my own reports, I would rather explain an uncertainty than conceal it behind a firm-sounding sentence. Medico-legal opinions frequently deal in probability rather than certainty. Pretending otherwise does not strengthen the report.
It usually makes it easier to challenge.
Causation is often the real dispute.
Many disputes that appear to concern diagnosis are, on closer examination, disputes about causation.
The medical condition itself may attract little disagreement. The real argument concerns whether the defendant’s conduct, the accident, the treatment or another event materially contributed to that condition.
That is why causation remains one of the more demanding parts of medico-legal practice. It calls for clinical knowledge, careful consideration of the records and an ability to deal properly with uncertainty.
It also requires discipline.
Experts must distinguish between what the evidence supports, what remains medically possible and what they consider probable. Those categories should not quietly merge into one another simply because a case appears straightforward.
The reports that withstand scrutiny best are rarely those containing the most emphatic opinions. They are usually the reports in which the expert has shown the reasoning, addressed the inconvenient evidence and made clear where the limits of the opinion lie.
A solicitor, insurer or claims handler may accept or challenge that conclusion.
They should not have to guess how the expert reached it.
