By Dr Mike Sidery, Consultant in Anaesthetics and Pain Management | Experienced Expert Witness at Pain Expert.
Chronic pain can be genuine, severe, and disabling even in the absence of demonstrable physical pathology. In medico-legal contexts, however, diagnosis alone does not establish causation. Where biological markers are absent, expert opinion must distinguish carefully between diagnostic legitimacy and causal inference, applying disciplined reasoning that recognises uncertainty, alternative explanations, and the potential influence of context — including litigation itself.
Introduction
Few areas of personal injury litigation generate as much conceptual difficulty — or as much evidential risk — as chronic pain without demonstrable or relevant physical pathology.
Such cases require courts, insurers, and medical experts to engage with an uncomfortable but well-recognised reality: pain may be subjectively severe and functionally disabling, yet lack a clear anatomical lesion or objective biomedical marker. In these circumstances, the distinction between diagnosis and causation becomes not merely academic, but determinative.
These issues were examined by Dr Mike Sidery at the Pain Expert Conference (November 2025), in a presentation addressing how chronic pain without relevant physical pathology should be understood, classified, and reasoned about in medico-legal contexts.
What Is a Diagnosis — and What Is It Not?
A diagnosis is a descriptive classification. It represents the outcome of a clinical process in which reported symptoms, observed behaviours, and functional impact are grouped within a recognised diagnostic category. Crucially, a diagnosis does not require explanation of underlying mechanism.
In clinical medicine, this distinction is often unproblematic. Diagnosis enables access to treatment even where mechanisms remain uncertain.
In medico-legal work, however, diagnosis is frequently treated as a proxy for causation. It is at this point that conceptual slippage — and evidential risk — arises.
Diagnosis and causation are distinct constructs, serving different purposes and operating under different standards of proof.
Diagnosis and Causation: Different Questions, Different Standards
In litigation, causation is the gateway to legal responsibility and financial attribution. It requires an opinion not simply that a condition exists, but that it arose because of a particular event, exposure, or breach.
Causation cannot be directly observed. It is inferred from available evidence, using inductive reasoning. At best, an alleged cause can be said to increase the probability of an outcome; it can never be established with certainty.
This epistemic limitation is present in all medico-legal causation analysis. It becomes especially salient in cases of chronic pain without physical pathology, where objective corroboration is limited or absent.
How Experts Actually Reason About Causation
Despite its centrality, there is no universally applied or formally standardised methodology for causation analysis in forensic medicine.
In practice, expert reasoning tends to fall into two broad approaches:
- Intuitive reasoning, grounded in clinical experience, pattern recognition, and narrative coherence
- Probabilistic reasoning, informed by epidemiology and structured criteria such as the Bradford Hill considerations
Both approaches have value. Both are vulnerable to error if applied without discipline.
Intuitive reasoning risks cognitive fallacies, particularly post hoc ergo propter hoc — the assumption that temporal sequence implies causation. Probabilistic reasoning depends on the availability of meaningful population data, biological plausibility, and reproducibility, which may be limited in conditions defined primarily by subjectivity.
Chronic Primary Pain and the Limits of Biomedical Explanation
ICD-11 recognises Chronic Primary Pain as a legitimate diagnostic entity. The classification explicitly acknowledges the contribution of biological, psychological, social, environmental, and genetic factors, while remaining agnostic as to specific cause.
By definition, Chronic Primary Pain:
- lacks a demonstrable biomedical marker
- is accepted as subjective
- is associated with significant distress or functional impairment
- is not better explained by another condition
Clinically, this classification is valuable. It allows patients to be diagnosed and treated without implying fabrication or malingering.
Medico-legally, however, its implications are more complex.
The Central Medico-Legal Problem
The core difficulty is not whether Chronic Primary Pain exists. It is whether — and on what basis — a causal link can be established between an index event and the onset or persistence of symptoms.
Where there is no lesion, no biological gradient, and no objective pathology, causation rests heavily on inference, proportionality, and careful evaluation of alternative explanations.
This raises a further question of formulation: when does Chronic Primary Pain represent a genuinely idiopathic condition, and when might it be more appropriately conceptualised as Chronic Secondary Pain, with psychological, contextual, or environmental factors playing a contributory role?
Lessons from Long COVID and Fibromyalgia
Conditions such as Long COVID and fibromyalgia illustrate these challenges clearly.
In both, prevalence has increased rapidly, diagnostic boundaries remain contested, and biological mechanisms are incompletely understood. The literature demonstrates associations with psychological distress, perceived stress, and social context, without establishing a definitive mechanistic pathway.
These conditions underline a critical point: diagnostic legitimacy does not equate to causal clarity.
Litigation as a Context, Not a Neutral Variable
The legal process itself is not psychologically inert.
Evidence indicates that individuals engaged in ongoing litigation often report higher distress and poorer functional outcomes than non-litigating counterparts, even following pain management interventions. Litigation may amplify attention, emotional learning, expectation, and threat processing.
This does not imply fabrication or exaggeration. It does, however, mean that litigation context can become an active component in symptom persistence — a factor that warrants acknowledgement rather than omission.
Diagnostic Rigour and Professional Discipline
In this evidential landscape, expert opinion demands particular discipline.
Key questions should be addressed explicitly:
- How confident is the proposed line of causation, and on what evidential basis?
- Is the formulation clinically credible and proportionate to the available evidence?
- Have alternative explanations been properly explored?
- Is deployment of a Chronic Primary Pain diagnosis necessary, or merely convenient?
- Have psychological, social, and contextual factors — including litigation — been adequately considered?
Diagnostic rigour is not scepticism. It is professional responsibility.
Conclusion
Chronic pain without demonstrable physical pathology sits at the boundary of what medicine can currently explain, and well within what the law must nevertheless decide.
In medico-legal contexts, the task is neither to deny suffering nor to manufacture certainty. It is to reason carefully, proportionately, and transparently about causation in the absence of biological proof.
When experts respect the limits of knowledge while applying disciplined analysis, pain and psychiatric evidence can assist the court without over-reach. That discipline is not optional. It is the difference between explanation and speculation.
If You’re a Legal Professional
Secure independent, first-time-right pain evidence that reduces dispute and keeps cases progressing.
If You’re a Pain Expert
Build a sustainable medico-legal practice with selective instructions, rigorous QA and full administrative support.
FAQs
- Can chronic pain exist without physical pathology?
Yes. Chronic pain may be genuine and disabling even in the absence of identifiable structural or biomedical abnormalities. - Does a diagnosis of Chronic Primary Pain prove causation?
No. Diagnosis describes a condition; it does not, of itself, establish that a specific event caused it. - Why is causation difficult in chronic pain cases?
Because causation must be inferred rather than observed, particularly where objective pathology is absent. - How should medico-legal experts approach these cases?
With disciplined reasoning, explicit acknowledgment of uncertainty, and careful consideration of alternative explanations and contextual factors. - Does litigation affect chronic pain outcomes?
Evidence suggests litigation context may influence distress and symptom persistence, without implying fabrication.
