By Dr Tom Bendinger, Consultant in Pain Medicine and Pain Medicine Expert Witness.
ICD-11 gives chronic pain litigation a clearer clinical framework. That matters because chronic secondary post-traumatic pain, CRPS, and chronic primary pain are not interchangeable, and the classification adopted may materially affect causation, prognosis, treatment, disability, and the interpretation of apparent inconsistency. In practice, many of the most difficult pain claims turn on precisely those issues.
A more useful framework for difficult pain cases
The modern definition of pain adopted by the International Association for the Study of Pain describes it as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.” That matters because it reflects what clinicians and courts often see in practice: pain is not always a straightforward proxy for demonstrable tissue injury.
ICD-11 builds on that by recognising chronic pain as a condition and separating it into chronic primary pain and several categories of chronic secondary pain. This is first recognition of pain as a separate entity since the creation of ICD in 1893. Those secondary categories include chronic post-surgical or post-traumatic pain, chronic secondary musculoskeletal pain, chronic neuropathic pain, chronic secondary headache or orofacial pain, chronic secondary visceral pain, and chronic cancer-related pain.
Chronic secondary pain, CRPS, and chronic primary pain are not interchangeable
One of the most important practical points is that chronic secondary post-traumatic pain, CRPS, and chronic primary pain should not be treated as interchangeable.
Chronic secondary post-surgical or post-traumatic pain is chronic pain that develops or increases in intensity after tissue trauma, whether surgical or accidental, and persists beyond three months. In medico-legal terms, these cases are often best understood through a bio-psycho-social model. Management is likely to be bio-psycho-social. Prognosis is often guarded and may be permanent. There may also be an increasing divergence between the underlying medical picture and the way the impact of pain is described in day-to-day functioning, which is where questions of surveillance, inconsistency, and fundamental dishonesty sometimes begin to arise.
CRPS remains a distinct clinical diagnosis. But that does not mean every difficult post-traumatic pain presentation falls within it. In some medico-legal cases, a presentation that has been treated as CRPS may, on closer analysis, be better understood as chronic secondary post-traumatic or post-surgical pain. Misidentification matters. Once the wrong label is accepted, it can affect the whole structure of the claim: the causation narrative, the expected prognosis, the treatment pathway, and the interpretation of the claimant’s presentation over time.
Chronic primary pain is different again. ICD-11 defines it as chronic pain in one or more anatomical regions characterised by significant emotional distress or functional disability, where the pain is not better accounted for by another chronic pain condition. The criteria include pain present for more than three months, together with emotional distress due to the pain or interference with daily activities and social participation. Critically, there is no better alternative chronic pain diagnosis to account for the presentation.
That distinction is not academic. In litigation, the diagnosis influences the questions an expert can properly answer and the confidence with which those answers can be given.
Why chronic primary pain creates difficulty in litigation
Chronic primary pain is often the most challenging category in pain medico-legal practice because the causation analysis is rarely straightforward.
Common examples include fibromyalgia and claims following low-speed road traffic accidents where there is low back pain or widespread pain without a clear biological explanation. Typical features include pain as the index complaint, a presentation consistent with central sensitisation, multiple risk factors for chronic primary pain, disability out of proportion to the biological injury, significant psychological comorbidity, and significant social problems or secondary gain issues.
Those features are precisely why these cases generate dispute. The question is not usually whether there was an accident. Nor is it always whether pain is genuinely being experienced. The real difficulty is how to analyse the relationship between the index event and the later chronic pain state without clear biological association and the existence of multiple risk factors or vulnerabilities. ‘Eggshell’ skull vs ‘crumbling’ skull rule maters for the causation.
In that context, causation needs to be framed carefully. The relevant questions may include whether the accident acted as a catalyst to a pre-existing condition through acceleration or exacerbation, whether it was the trigger in a but-for sense, or whether it made a material contribution to a more complex pain presentation.
That is a more realistic approach than asking only whether the original injury, viewed narrowly as a tissue event, can fully explain the current symptoms. Chronic primary pain often does not lend itself to that kind of linear reasoning. The absence of a clear biological mechanism does not make the presentation unreal. But it does require discipline from the expert. Opinion in this area must be built from chronology, prior symptoms, vulnerability factors, contemporaneous records, and the way the presentation has evolved over time.
Disproportionality does not answer the case
One of the recurring features of chronic pain litigation is apparent disproportionality. The injury may appear modest. The reported symptoms and disability may appear substantial. The temptation is to treat that mismatch as the answer. It is not.
Disproportionality may be a feature of chronic primary pain. It may also raise questions about inconsistency, amplification, alternative diagnosis, or, in some cases, more serious concerns about the reliability of the presentation. The important point is that it must be analysed rather than assumed away, but also not overstated.
That is why prognosis matters. Better outcomes are associated with early diagnosis, multidisciplinary treatment, resilience and adaptive coping, and maintenance of physical activity and social roles. Poorer outcomes are associated with pain catastrophising, depression, anxiety, PTSD, social isolation, ongoing litigation, and over-reliance on medication.
For a legal audience, the significance is obvious. These factors may affect the future course of symptoms, the reasonableness of treatment recommendations, and the extent to which a chronic pain condition is likely to become entrenched. They may also help explain why a claimant with apparently limited tissue injury presents with long-term disability. But explanation is not the same as automatic acceptance. The expert’s task is still to assess whether the overall picture is medically coherent.
The treatment point follows the same logic. Management in chronic pain cases, particularly chronic primary pain, must reflect the complexity of the condition rather than a narrow search for a purely structural lesion that explains everything.
Range of opinion matters, especially in chronic primary pain
One of the most important medico-legal features of chronic primary pain is that there may be a genuine range of reasonable clinical opinion.
That range may include chronic secondary pain where a biological mechanism can be established. It may include conscious or unconscious exacerbation of the condition in the presence of inconsistencies. In some cases it may extend to malingering, fundamental dishonesty, or an alternative diagnosis outside pain medicine.
That does not mean every chronic primary pain claim is inherently suspect. It means something more disciplined: that these cases cannot be approached with a single stock narrative. Some will involve genuine chronic pain disorder. Some will involve a mixture of genuine symptoms and exaggerated presentation. Some will be better explained by psychiatric or neurological formulation. Some will raise serious evidential concerns. The expert’s job is not to choose a theory by instinct, but to analyse the material carefully enough to justify one.
This is also where the limits of expert evidence need to be respected. A pain expert can identify inconsistency, critique diagnosis, analyse chronology, and assess whether the reported disability is medically coherent. But legal findings remain for the court. Clinical inconsistency is not the same thing as legal dishonesty, even if one may become relevant to the other.
That distinction matters particularly in the context of surveillance. Surveillance may be highly relevant to function and consistency. It may expose mismatch between presentation and activity. What it cannot do, on its own, is determine whether pain is or is not present, or answer every medico-legal question in the case. It remains one part of a wider evidential analysis.
Why cross-speciality differences matter
Chronic primary pain also creates difficulty because similar symptom patterns may be described differently across specialities.
From a psychiatric perspective, the symptoms may form part of bodily distress disorder (BDD) or somatic symptom disorder (SSD), where persistent bodily symptoms lead to distress and preoccupation sufficient to impair daily functioning. From a neurological perspective, similar features may be framed as functional neurological disorder (FND), involving abnormal function in a system capable of normal function.
That overlap does not necessarily reveal contradiction. It may simply reflect the fact that persistent pain symptoms often sit across disciplinary boundaries. For lawyers, the practical importance lies in understanding what each formulation explains, what it does not explain, and whether the expert is remaining within the proper limits of their own expertise.
What a proper medico-legal pain assessment should do
In difficult pain claims, the quality of the medico-legal reasoning matters more than the confidence of the language.
A proper assessment begins with the records. It requires critical appraisal of the historic diagnosis rather than mere repetition of it. It requires a composite chronology of complaints, because in chronic pain litigation timing is often decisive: what was reported, when it was first reported, how symptoms evolved, whether the pain picture broadened over time, and whether there were relevant symptoms or vulnerabilities before the index event.
It also requires detailed examination and careful identification of inconsistencies. A label that appears repeatedly in the notes is not necessarily the right diagnosis. That is particularly important where CRPS has been suggested, or where a persistent pain presentation may fit better within chronic secondary or chronic primary pain.
Just as importantly, diagnosis, causation, prognosis, and consistency need to be kept separate. They are related questions, but they are not the same question. Some medico-legal reports go wrong because they answer one and assume the others follow automatically.
A careful pain report should do the opposite. It should explain the diagnosis. It should identify the possible causation formulations. It should address prognosis with appropriate restraint. It should analyse consistency without straying into legal conclusions reserved to the court. In a contested pain claim, that kind of rigour is more useful than a superficially certain opinion.
Conclusion
ICD-11 gives lawyers and experts a clearer clinical framework for some of the most difficult cases in pain litigation. It does not remove dispute, and it does not change the legal tests. What it does do is improve the quality of the medical analysis where classification, causation, prognosis, and evidential reliability are all in issue.
The central lesson is a simple one. Chronic secondary post-traumatic pain, CRPS, and chronic primary pain are not interchangeable labels. In the right case, the distinction may materially affect the whole medico-legal analysis.
For those instructing experts, the practical questions remain the same. What is the most accurate diagnosis on the records and examination? Does the chronology support it? What is the proper causation model? Is the reported disability medically coherent? Is there a genuine range of opinion? And where inconsistency exists, what does it properly show?
Those are the questions that make chronic pain evidence useful to the court.
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FAQs
What is chronic primary pain in medico-legal terms?
It is a chronic pain condition involving persistent or recurrent pain for more than three months, with emotional distress or functional disability, where the presentation is not better explained by another chronic pain condition. In litigation, it often arises where symptoms persist without a clear biological explanation.
How is chronic primary pain different from chronic post-traumatic pain?
Chronic post-traumatic pain is a form of chronic secondary pain developing or increasing after tissue trauma and persisting beyond three months. Chronic primary pain applies where the pain is not better accounted for by another chronic pain condition and where emotional distress or functional impairment form part of the picture.
Does ICD-11 remove CRPS?
No. CRPS remains a recognised diagnosis. The important point is that some cases may be better understood as chronic secondary post-traumatic or post-surgical pain rather than CRPS.
Can a low-speed road traffic accident lead to chronic primary pain?
It may do so in some cases, but the analysis is rarely straightforward. The relevant questions may include whether the accident acted as a trigger, whether it accelerated or exacerbated a pre-existing condition, or whether it made a material contribution to a more complex pain presentation.
Does inconsistency automatically mean fundamental dishonesty?
No. Inconsistency is a clinical and evidential issue. Fundamental dishonesty is a legal conclusion for the court. An expert may identify inconsistencies and explain their significance, but should not collapse that distinction.
Why does classification matter so much in a legal claim?
Because the classification may affect the analysis of causation, prognosis, treatment, and the interpretation of reported disability. In a difficult chronic pain claim, the wrong label can distort the entire medico-legal analysis.
