FND: Moving away from incongruence as a diagnostic tool

In this month’s update from our Functional Neurological Disorder (FND) SIG, we look at the criteria for diagnosing FND, signs to be aware of, and what the future holds.

FND refers to a wide range of neurological symptoms that cannot be explained by disease or structural damage, thought to be from changes in brain networks rather than brain structure. If you haven’t already, make sure to download our FND handling guide which includes tips for dealing with claims.

Diagnosing FND

Disciplines that assist in diagnosing FND include neurology, neuropsychiatry and neuropsychology, however others may be required depending on the facts of the case.

The criteria for diagnosis include:

1. One or more symptoms of altered voluntary motor or sensory function.
2. Clinical findings that provide evidence of incompatibility between the symptoms and recognised neurological or medical conditions.
3. The symptom or deficit is not better explained by another medical or mental disorder.
4. The symptom or deficit causes clinically significant distress or impairment in social, occupational, or other important areas of functioning or warrants medical evaluation.

As mentioned in one of our previous FND articles, inconsistency (the variability in performance under voluntary vs automatic control) and incongruence (the symptoms defy known anatomical or physiological laws) are thought to be the two main pillars of a positive FND diagnoses.

Inconsistency and incongruence

Prof Jon Stone (neurologist) recently provided his perspective on moving away from using incongruence to diagnose FND.

In his article, Prof Stone argues for abandoning incongruence as a diagnostic criterion in FND, citing its limitations and proposing a more constructive approach. He outlines the following criticisms:

1. Making a diagnosis of exclusion: incongruence focuses on what a symptom is not, making it an insecure and unsatisfactory diagnostic method.
2. Applying incongruence requires omniscience in clinical neurology: diagnosing based on incongruence requires an all-encompassing understanding of neurology, which is not practically achievable.
3. It is not future proof: symptoms deemed incongruent today may later align with newly identified conditions in the future, and FND should not be diagnosed just because it is thought to be ‘bizarre’.
4. Incongruence presumes complete knowledge of anatomy: there is a better understanding of how the brain works, with the predictive processing model of brain function often explaining hard to understand conditions.

An example of positive diagnostic features

Prof Stone highlights the value of positive diagnostic features, using an example of a patient with functional freezing of gait (freezing of gait in Parkinsonism is superficially a phenomenon very similar to functional movement disorder), and whether incongruence is really required to make an FND diagnosis when there are:

1. Features of internal inconsistencies e.g. sometimes able to completely lift a foot off the ground during stepping, while at other times unable to do so.
2. Traits that appear unique to a functional disorder causing freezing of gait, such as amplified responses following a shoulder tap, or running movement with arms despite no leg movement.
3. Features that are the same in both disorders, but which can be interpreted differently by other features on assessment i.e. freezing of gait without Parkinsonism/typical non-motor features substantially raises the chance it is FND-related.

There are types of FND other than motor symptoms, such as functional seizures, which are said to be incongruent with epileptic seizures, however they also have their own range of typical features (eyes closed, long duration, tremor-like movements etc) and again Prof Stone argues incongruency is not necessary for recognising FND.

Conclusion

Prof Stone urges clinicians to diagnose FND using characteristic features and internal inconsistencies, bringing its diagnosis in line with other neurological conditions. Moving away from incongruence as a diagnosis in FND may improve accuracy and patient care, focusing on what is happening to cause the experience rather than focusing on what those experiences are not.

Comment

FND is an ever-evolving, complex area. Prof Stone highlights a shift away from relying on incongruence to recognise clinical features in FND, and instead use a more practical, patient-focused approach which can improve diagnosis and subsequent care.

In the context of a personal injury claim, this shift may facilitate a more accurate and timely diagnosis in a claim, leading to more effective treatment pathways for claimants and an improved chance of returning to their pre-accident level of functioning. For further discussion on treatment, check out our recent article on a study involving functional motor disorder.

Specialist advice is recommended for potential claims involving FND. Our Special Interest Group members are always happy to discuss individual cases with such characteristics and provide guidance on strategies for handling and progressing claims.

Ryan Rogers
Associate