What is FND?

A functional neurological disorder (FND) is a collection of signs and symptoms that refer to genuinely experienced changes in motor, sensory or cognitive functioning. The main pathophysiological processes involve altered functioning of brain networks and refer not to damage to brain structures but to dysfunctional functioning of the central nervous system. FND is the result of a complex combination of the impact of biological, psychological and social factors on the brain (Aybek and Perez, 2022; Bennet et al., 2021; Gilmour et al., 2020). is the result of a complex combination of the impact of biological, psychological and social factors on the brain (Aybek and Perez, 2022; Bennet et al., 2021; Gilmour et al., 2020).

As a disorder at the interface between neurology and psychiatry, it has historically borne the burden of many names such as conversion disorder, psychogenic disorder and and even hysteria, but in the last 10 years it has been experiencing a clinical renaissance due to new neuroscientific findings (Bennet et al., 2021).

  • HYSTERIA

    The term "Hysteria" comes from the Greek word 'hystera', which translates to 'womb'. It was first used in the 19th century to diagnose physical conditions in women. Over time, especially in the 20th century, with the influence of Sigmund Freud, Jean-Martin Charcot, and Janet, it shifted to describe mental health problems in women. Nowadays, 'hysteria' is no longer regarded as a valid medical diagnosis because it suggests that the person is overly emotional and irritable, among other characteristics.

  • PSYCHOSOMATIC DISORDER

    The term psychosomatics originates from the Greek words 'psyche' meaning 'mind' and 'soma' meaning 'body'. A psychosomatic disorder is a condition that impacts both mental and physical health. It can be suggested that most disorders have a psychosomatic foundation, as mental aspects like stress can sometimes contribute to the onset of physical ailments. Psychosomatics highlights the interplay between bodily functions and mental well-being, showing how each can influence the other.

  • CONVERSION

    Functional Neurological Disorder was previously known as 'Conversion Disorder' in the DSM-IV psychiatric diagnostic manual. However, in 2022, the DSM-V updated the name to Functional Neurological Symptom Disorder (Conversion Disorder), providing a more neutral and accurate term for FND. The concept of 'conversion' can be traced back to Sigmund Freud's work, where he used it to explain the process of turning psychological stress into physical symptoms.

  • NERVOUS SYSTEM DISORDER

    A nervous system disorder signifies a malfunction in the nervous system, which can be caused by various factors like infections, brain and spinal cord injuries, degenerative diseases such as Parkinson's or Alzheimer's disease, epilepsy, mental disorders, autoimmune diseases, and more. Unlike patients with other nervous system impairments, those with Functional Neurological Disorder (FND) exhibit dysfunctional or inadequately controlled nervous system activity, making the term "Functional Neurological Disorder" more accurate.

  • DISORDER WITH DISSOCIATIVE NEUROLOGICAL SYMPTOMS

    The International Classification of Diseases (ICD, 2019) defines dissociation as a separation of neurological function from normal awareness. People with Functional Neurological Disorder (FND) experience seizures classified as psychogenic and/or non-epileptic seizures, sometimes referred to as dissociative seizures. These seizures are also called pseudoseizures, indicating that the symptoms are not authentic.

  • NONORGANIC DISORDER

    An organic disorder or disease shows measurable changes in organ or body systems, whereas a functional disorder displays alterations in function without accompanying measurable changes in organ or body systems. It is essential to note that a functional disorder should not be dismissed as 'false' simply because it cannot be identified through tests that measure physical changes. Recent neuroscientific studies have revealed varying structural and functional brain activity in patients with Functional Neurological Disorders (FND).

  • PSYCHOGENIC DISORDER

    The concept implies that the disorder arises solely from psychological sources. While we acknowledge the influence of psychological risk factors, triggers, and factors that sustain the condition, it is inaccurate to equate causes with risk factors.

Is the cause of the disorder exclusively psychological?

FND is often interpreted as a mere 'psychological reaction' or 'a disorder resulting from stress or trauma'. These explanations do not take into account the broad spectrum and complexity of the disorder itself, but can also lead to psychological distress, manifested in patients' feelings of not being believed, alienation and stigmatisation (Cock and Edwards, 2018).

The problem with this explanation of the disorder is that it equates risk factors with the cause of the disorder itself (e.g. most FND patients have a history of a traumatic event, but it cannot be said that the cause of the FND is a past stressful life event).

The problem also arises when the usual communication of medical professionals implicitly communicates that the cause is entirely psychogenic in nature, thus trivial or even inauthentic, thus ignoring the fact that the diagnosis was made on the basis of positive physical symptoms and signs.

In the vast majority of patients, the disorder is triggered by a specific medical intervention, such as surgery, infection or trauma, and it is helpful to acknowledge the reality of the trigger, while explaining that functional symptoms develop independently of the nervous system injury after the trigger (Cock and Edwards, 2018).

Epidemiology

Functional neurological disorder is the second most common reason to see a neurologist after headache, with around 8,000 new diagnoses in the UK each year. It can occur at any age and disproportionately affects the female sex (3:1), although the proportion of males diagnosed also increases with increasing age (Bennet et al., 2021).

Hardware vs Software analogy

In clinical practice, the metaphor of computer hardware is often used, where the hardware is intact (i.e. the brain), while the problem lies in the software (i.e. how the brain and body bilaterally receive and transmit signals). Underlying this analogy is the assumption that FND is a disruption of the mind-body connection and that further treatment will be aimed at reconnecting them, revealing the potential reversibility of the condition (Gilmour et al., 2020).

While this analogy is useful, it is a vague description of the disorder itself, as it does not include an explanation of the mechanisms, the factors that perpetuate the disorder and the next steps that will lead to a potential cure (Van der Hulst, 2023). As a result, the Pressure Cooker Model( PC Model) analogy is slowly gaining ground in practice, explaining all elements of the disorder in language that is understandable to the patient, while at the same time being visually easy to understand and remember. You can read more about the PC model here.

    • Aybek, S., and Perez, D. L. (2022). Diagnosis and management of functional neurological disorder. bmj, 376.

    • Bennett, K., Diamond, C., Hoeritzauer, I., Gardiner, P., McWhirter, L., Carson, A., and Stone, J. (2021). A practical review of functional neurological disorder (FND) for the general physician. Clinical Medicine, 21(1), 28.

    • Cock, H. R. and Edwards, M. J. (2018). Functional neurological disorders: acute presentations and management. Clinical medicine, 18(5), 414.

    • Gilmour, G. S., Nielsen, G., Teodoro, T., Yogarajah, M., Coebergh, J. A., Dilley, M. D., and Edwards, M. J. (2020). Management of functional neurological disorder. Journal of Neurology, 267, 2164-2172.

    • van der Hulst, E. J. (2023). A Clinician's Guide to Functional Neurological Disorder: A Practical Neuropsychological Approach. Routledge.