Avoiding reasoning errors in psychiatric injury reports: PTSD claims after road traffic accidents

Diagnostic criteria and evidential foundations

In claims for Post-Traumatic Stress Disorder (PTSD) following a road traffic accident (RTA), the expert psychiatric report must apply the diagnostic criteria set out in the DSM-5-TR or ICD-11. The expert’s role under CPR Part 35 is to provide an independent opinion on whether the claimant’s presentation meets these criteria. A common error is conflating general post-traumatic distress with the specific symptom clusters required for a PTSD diagnosis.

The report should establish whether the claimant experienced a qualifying traumatic event, such as an RTA involving an objective threat of serious injury or death. The expert must document the presence of core symptom clusters, including:

• Intrusive re-experiencing (e.g., flashbacks, nightmares);
• Persistent avoidance of trauma-associated stimuli;
• Negative alterations in cognition and mood;
• Marked alterations in arousal and reactivity.

An opinion that relies solely on the occurrence of an accident, without clinical evidence of these symptom clusters, is unlikely to satisfy the court on the balance of probabilities.

The role of primary records

The robustness of a psychiatric opinion depends on the contemporaneous record base. The expert should review primary care records, ambulance service reports, and emergency department attendance notes following the accident. A frequent error is over-reliance on the claimant’s self-reported timeline of symptom onset while disregarding documented evidence of pre-existing mental health conditions or life stressors.

Under CPR 35.10, the expert’s report must state the substance of all material instructions, including the documents provided. If primary records are incomplete or absent, the expert should explicitly acknowledge this limitation. For example, if the expert is unaware of a prior diagnosis of anxiety or depression, they may incorrectly attribute current symptoms to the index accident, rather than considering whether the accident exacerbated a pre-existing condition.

Causation: Applying the but-for test

Legal causation in psychiatric injury claims requires demonstrating that the PTSD would not have occurred but for the RTA. A common reasoning error is conflating the presence of symptoms with their cause. The expert must evaluate whether the claimant’s current psychological state is the natural and direct consequence of the accident-related trauma.

Where the claimant had a pre-existing vulnerable psychological profile, the expert must distinguish between symptoms attributable to the index event and those that would have occurred regardless. The but-for test remains the primary framework for causation in most cases. A material contribution analysis may be considered only in exceptional circumstances where the law recognises it as applicable.

Discipline boundaries and scope of expertise

Psychiatric evidence in RTA claims is limited to the diagnosis, treatment, and prognosis of psychological injury. Experts frequently err by commenting on matters outside their clinical competence, such as the mechanics of the collision or the severity of vehicle impact. These issues are for the court to determine, not the psychiatric expert.

Where a case involves potential cognitive deficits following a head injury, a neuropsychological assessment may be required to distinguish between organic brain injury and a psychological reaction to trauma. A psychiatrist may not be qualified to provide diagnostic clarity on neurocognitive impairment, and a psychologist may lack the expertise to comment on psychopharmacological interventions. The expert must recognise the limits of their discipline and recommend additional evidence where necessary.

Procedural integrity under CPR Part 35

The expert’s overriding duty to the court, as set out in CPR 35.3, requires absolute independence. Reasoning errors may be identified during discussions between experts, which may be directed by the court or arranged where appropriate under CPR 35.12. The expert must engage constructively but must not advocate for the instructing party’s position.

Where two experts are instructed, discrepancies in clinical notes or diagnostic methodology may be clarified through written questions under CPR 35.6. This process allows for the resolution of uncertainties without requiring a full re-evaluation. If an expert’s opinion is inconsistent with the medical records, the court may give it limited weight, regardless of the expert’s professional standing.

The reliability of an expert opinion is assessed on the quality of reasoning, not the length of the report. A logical, evidence-based report that acknowledges gaps in the medical history and distinguishes between the index accident and pre-existing factors is more likely to assist the court in resolving disputes over causation and prognosis.