Functional Neurological Disorder (FND) in Medicolegal Cases: A Guide for Solicitors

Functional Neurological Disorder (FND) presents unique challenges in abuse injury litigation. In the experience of medico-legal psychiatrists and psychologists, FND is frequently encountered in claimants who have sustained prolonged or severe trauma, including alleged abuse in childhood, institutional settings, or domestic environments. This guide explains the clinical context, legal relevance, and expert witness considerations for solicitors instructing in cases where FND is a feature.

Clinical Context: Understanding FND in Trauma Survivors

FND is recognised in both ICD-11 and DSM-5 as a condition involving genuine neurological symptoms—such as limb weakness, seizures, or sensory disturbances—that are not attributable to structural neurological disease. Instead, symptoms arise from altered nervous system functioning, often in the context of psychological distress or trauma. In abuse injury medico-legal practice, FND may emerge as a somatic expression of underlying complex trauma, particularly where emotional regulation and bodily awareness have been disrupted by sustained interpersonal harm.

Key clinical features include:

• Symptom variability and inconsistency with known neurological patterns
• Positive clinical signs (e.g., Hoover’s sign in functional weakness, entrainment in functional tremor)
• Co-occurrence with psychiatric conditions such as PTSD, complex PTSD, or dissociative disorders
• Onset or exacerbation following emotional triggers, including reminders of alleged abuse

In child abuse cases, developmental trauma and attachment disruption may contribute to early somatic presentations, while in historic abuse claims, delayed disclosure and betrayal trauma theory are often relevant to understanding symptom emergence. The Adverse Childhood Experiences (ACEs) study further supports the link between early trauma and later functional neurological presentations.

Legal Relevance: Where FND Arises in Abuse Injury Claims

FND may be central to civil claims for personal injury, CICA applications, or group litigation involving institutional abuse. Its relevance spans multiple legal domains:

Civil Claims and Causation

In claims alleging psychological injury following alleged abuse, FND may form part of the clinical picture. Under the principles established in Smith v Leech Brain & Co Ltd [1962] 2 QB 405 (eggshell skull rule), a defendant must take the claimant as they find them—including pre-existing vulnerabilities that may shape symptom expression. Expert opinion may address whether the alleged abuse was a material contributory cause of the FND, particularly where complex PTSD or dissociative symptoms are also present.

In historic abuse claims, limitation arguments under the Limitation Act 1980 Section 33 may turn on the claimant’s capacity to recognise or articulate harm at the time. The House of Lords’ decision in A v Hoare [2008] UKHL 6 and the Court of Appeal’s guidance in KR v Bryn Alyn Community (Holdings) Ltd [2003] EWCA Civ 85 emphasise the need for expert evidence on delayed disclosure and the clinical science of memory in trauma.

CICA and Mental Injury Tariffs

Under the Criminal Injuries Compensation Scheme, FND may qualify as a “mental injury” if it results from a crime of violence. The Scheme’s tariff framework (Bands 1–15) requires expert assessment of symptom severity and functional impairment. Post-2019 reforms removed the “same-roof rule,” but time limits and unspent convictions remain relevant. Expert reports must align with CICA’s requirement for “good reasons” to extend time limits, particularly where delayed disclosure is a factor.

Institutional and Vicarious Liability

In claims against institutions (e.g., schools, care homes, religious organisations), FND may feature in allegations of systemic failure. The Supreme Court’s decisions in Various Claimants v Barclays Bank plc [2020] UKSC 12 and Armes v Nottinghamshire County Council [2017] UKSC 61 establish the tests for vicarious liability. Expert evidence may address whether the institution’s safeguarding failures contributed to the development or exacerbation of FND, particularly in cases involving prolonged exposure to harm.

Common Pitfalls and Disputes in FND Cases

Several recurring issues arise when FND is poorly understood in medico-legal contexts:

Diagnostic Overreach and Misattribution

FND is a diagnosis of inclusion, not exclusion. It requires positive clinical signs and a thorough neurological workup to rule out organic pathology. In abuse injury claims, there is a risk of misattributing symptoms to FND where structural causes (e.g., traumatic brain injury) have not been adequately investigated. A trauma-informed expert witness will ensure that the assessment is multidisciplinary, involving neurology where indicated.

Causation Errors

Defendants may argue that FND is unrelated to the alleged abuse, particularly where symptoms predate the index events or where other stressors (e.g., workplace stress, bereavement) are present. Expert opinion must carefully assess the temporal relationship between trauma exposure and symptom onset, as well as the role of pre-existing vulnerabilities. The “but for” test in Barnett v Chelsea and Kensington Hospital [1969] 1 QB 428 remains relevant, but in complex trauma cases, a “material contribution” approach may be more appropriate.

Malingering and Symptom Validity

FND is often mistakenly conflated with malingering or factitious disorder. In abuse injury claims, this can lead to secondary victimisation during cross-examination. Expert witnesses may use validated psychometric tools—such as the Structured Inventory of Malingered Symptomatology (SIMS), the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF), or the Test of Memory Malingering (TOMM)—to assess symptom validity. However, these must be interpreted with caution in trauma survivors, as elevated scores may reflect genuine dissociation or cognitive overload rather than fabrication.

Failure to Recognise Complex Trauma Presentations

FND rarely occurs in isolation. In abuse injury claims, it is frequently comorbid with complex PTSD (ICD-11), dissociative disorders, or somatic symptom disorder. A narrow focus on FND alone may lead to underestimation of the claimant’s overall impairment. Expert reports should adopt a holistic, trauma-informed approach, assessing disturbances in self-organisation (emotional dysregulation, negative self-concept, and relational difficulties) alongside functional neurological symptoms.

Role of the Expert Witness in FND Cases

The expert witness plays a critical role in bridging clinical and legal frameworks. Their report should:

• Provide a clear, jargon-free explanation of FND and its relationship to trauma
• Address the specific legal tests relevant to the claim (e.g., causation, limitation, quantum)
• Distinguish between FND and other conditions (e.g., conversion disorder, somatic symptom disorder)
• Assess symptom severity and functional impact using standardised measures (e.g., WHODAS 2.0, SF-36)
• Offer a prognosis, including the likelihood of improvement with trauma-focused therapy
• Comment on care needs, including psychological input, physiotherapy, and occupational therapy

Trauma-Informed Methodology

Assessment of FND in abuse injury claims requires a trauma-informed approach. This includes:

• Allowing the claimant control over the pace and structure of the interview
• Avoiding retraumatisation by not pressing for details of the alleged abuse unless clinically necessary
• Using grounding techniques if dissociation occurs during assessment
• Collaborating with treating clinicians where possible to ensure continuity of care

In cases involving children or vulnerable adults, the expert may need to liaise with paediatricians or Court of Protection specialists to ensure safeguarding considerations are addressed.

Multi-Disciplinary Input

FND cases often benefit from multi-disciplinary assessment. A psychiatrist may evaluate comorbid psychiatric conditions (e.g., PTSD, depression), while a clinical psychologist can administer psychometric testing and assess cognitive functioning. In cases involving physical symptoms (e.g., functional seizures), a neurologist may provide input on differential diagnosis. For solicitors, instructing a panel of experts from a single provider can streamline the process and ensure consistency of opinion.

Practical Guidance for Solicitors

When to Submit Case Enquiry

Early instruction is advisable where:

• FND is suspected based on medical records or the claimant’s account
• There are concerns about symptom validity or malingering
• Limitation arguments are likely to turn on the claimant’s capacity to recognise harm
• The claim involves complex trauma or institutional abuse

In CICA matters, an expert report may be necessary to justify mental injury tariff levels or to support an application for time limit extension.

Records to Provide

To enable a thorough assessment, instructing solicitors should provide:

• Medical records (GP, neurology, psychiatry, paediatrics)
• Therapy notes (if available)
• School or employment records (to assess functional impact)
• ABE interview transcripts (in child abuse cases)
• Previous medico-legal reports (if any)

Preparing the Claimant for Assessment

Claimants may feel anxious about medico-legal assessments, particularly if they have experienced previous disbelief or stigma around FND. Solicitors can support their clients by:

• Explaining the purpose of the assessment in clear, non-judgemental terms
• Reassuring them that the expert is trauma-informed and will not press for distressing details
• Encouraging them to bring a support person if helpful
• Advising them to take breaks if needed during the assessment

What to Expect from the Report

A high-quality medico-legal report in an FND case should:

• Clearly state the expert’s qualifications and experience in trauma and FND
• Summarise the claimant’s history and presenting symptoms
• Provide a differential diagnosis, ruling out organic causes
• Assess causation, addressing the legal tests relevant to the claim
• Comment on prognosis and care needs
• Be compliant with CPR Part 35 and the Civil Justice Council’s Guidance for the Instruction of Experts in Civil Claims

In single joint expert reports, the expert must remain impartial and address the questions posed by both parties.

Conclusion: The Importance of Trauma-Informed Expertise

Functional Neurological Disorder in abuse injury claims demands a nuanced, trauma-informed approach. For solicitors, instructing an expert witness with specialist experience in FND and complex trauma ensures that the claimant’s presentation is accurately assessed, causation is properly addressed, and the legal process is informed by the best available clinical evidence. Whether in civil claims, CICA matters, or group litigation, careful instruction of a medico-legal expert is pivotal—particularly where complex trauma presentations, limitation issues, or multi-disciplinary questions arise.