Functional Movement Disorder: When Motor Symptoms Defy Structural Explanation

In personal injury litigation, neurological symptoms often carry weight - particularly when they persist long after the initial trauma. Tremors, gait disturbances, and abnormal movements can suggest serious underlying pathology. But what happens when these symptoms are genuine and yet no structural damage can be found?

This is the clinical puzzle posed by Functional Movement Disorder (FMD), a condition that sits at the intersection of neurology and psychiatry, and one that is increasingly relevant in the assessment of injury claims.

A Disorder Hidden in Plain Sight

FMD is not new in a clinical context, but it has long been misunderstood. Patients present with involuntary movements - tremors, jerks, dystonia - that mimic organic conditions like Parkinson’s. Yet, unlike those disorders, FMD does not show up on scans. There is no lesion, no degeneration, and whilst this is an emerging area of research as we discuss further below, no overwhelmingly reliable biochemical markers.

A recent review Treatable Hyperkinetic Movement Disorders Not to Be Missed brings renewed clarity to this condition. It highlights the clinical features that distinguish FMD from its organic counterparts and stresses the importance of recognising it early, not only for the patient’s wellbeing, but also to avoid unnecessary investigations and misdirected claims.

The Diagnostic Challenge

FMD is often diagnosed by what it is not. But the review advocates for a more proactive approach - identifying positive signs that point to a functional origin. These include:

• Movements that change with distraction or suggestion
• Symptoms that fluctuate or disappear during sleep
• Inconsistencies in clinical presentation

For insurers, this distinction is critical. A claimant may present with disabling tremors or difficulty walking, yet if the neurological picture is normal, the assumption of brain injury may be misplaced. Recognising FMD can prevent misdiagnosis and ensure compensation reflects clinical reality.

The Search for Biomarkers

While FMD remains a clinical diagnosis, research is increasingly focused on identifying objective biomarkers to improve diagnostic confidence. A systematic review on biomarkers published in Neurologia i Neurochirurgia Polska categorised emerging evidence into the following domains:

• Genetic markers: Preliminary studies suggest that certain stress-related genes - particularly those involved in the serotonergic pathway - may influence symptom severity and recovery. For example, variants in the TPH1 and TPH2 genes have been linked to more severe symptoms and poorer outcomes.

• Biofluid biomarkers: Elevated levels of inflammatory markers such as IL-6, TNF-alpha, and VEGF have been observed in FMD patients, suggesting systemic low-grade inflammation. Neurotransmission markers like glutamate, dopamine, and BDNF also show altered levels, pointing to dysregulation in emotional and stress-related pathways.

• Electrophysiological tools: Techniques like Bereitschaftspotential (BP) and EMG variability show promise in distinguishing functional tremor and myoclonus from organic movement disorders.

Although these findings are still considered experimental, they reinforce the notion that FMD may not be simply a psychological condition, it may also have measurable biological correlates. For insurers, this emerging science may eventually support more robust, evidence-based assessments of functional claims.

FMD, FND and FCD: Drawing the Lines

FMD is part of a broader family of conditions known as Functional Neurological Disorders (FND). These encompass a wide range of symptoms, from seizures to sensory loss to limb weakness. FMD is the motor expression of this group.

By contrast, Functional Cognitive Disorder (FCD) involves cognitive complaints - memory lapses, attention deficits - that similarly lack structural explanation. While FCD and FMD share a functional origin, their presentations are distinct. FCD can be mistaken for post-concussion syndrome; FMD, for Parkinson’s or dystonia.

Understanding these differences matters. It allows insurers and those dealing with claims of this nature to tailor assessments, challenge unsupported diagnoses, and direct claimants toward appropriate care.

Treatment and Recovery: A Different Pathway

One of the most important insights from the review is that FMD is treatable. Recovery does not come from medication or surgery, but from multidisciplinary rehabilitation, including physiotherapy, psychological support, and education.

Patients who understand their diagnosis and engage with treatment often improve significantly. This has direct implications for claims management. Early recognition and referral can shorten recovery time, reduce claim costs, and avoid the pitfalls of long-term disability assumptions.

Why It Matters for Insurers

Functional disorders challenge traditional models of injury assessment. They require a shift from structural thinking to functional understanding. For insurers, this means:

• Asking the right clinical questions
• Seeking expert assessments from clinicians familiar with FMD
• Supporting rehabilitation, over compensation
• Recognising not all disabling symptoms stem from physical damage

FMD is not rare, but it is under-recognised, especially in a personal injury context. As awareness grows, so too does the opportunity to improve outcomes for claimants, clinicians, and insurers alike.

The Brain Injury Subject Matter Group regularly publishes blogs exploring the latest developments in this evolving area, including Functional Neurological Disorder. The Manchester and London CILL teams are also running a series of FND mock trials to focus on this important issue. If you would like to learn more or take part, please reach out to your usual Clyde & Co contact.