Functional Neurological Disorders: Challenging the Mainstream Agnostic Causative Position

Introduction

The classification of the so-called “functional” psychiatric disorders has long been debated. Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV; 1994) retained the “somatoform” psychological-primacy concept but had poorly devised subdivisions with criteria that proved too loose or too tight to be useful. ¹ The disorders were excluded from major health surveys and clinicians simply did not use the diagnostic categories. ² Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5; 2013) provided an opportunity for improvement, but instead of primarily addressing the weaknesses of DSM-IV, changes were made in a completely different direction: there was a fundamental shift away from the acknowledgement of psychological mechanisms being of central importance in functional disorders. Criteria requiring the clinician to judge conversion symptoms as being “associated with psychological stressors” were dropped; the transition from “conversion” to “functional neurological” was begun. “Somatoform” became the neutral “somatic symptom disorders”, ³ and there was a move away from the idea of “medically unexplained symptoms” (MUS): the DSM-5 workgroup felt that “medically unexplained” was synonymous with “psychiatric” and was thus to be avoided.^4–6 There was also a view that “…the MUS approach is not well accepted by patients who feel that MUS implies that their symptoms are inauthentic and ‘all in your head’”. ⁷ Overarchingly, DSM-5 adopted an attitude of agnosticism regarding the causation of these disorders. In the ensuing years this has morphed into a mantra: the idea that psychological factors are integral to these disorders rather than “co-morbid” is now deemed “radical”, ⁸ or “out of date”, ⁹ and psychiatrists are being encouraged to join the agnostic “renaissance”. ¹⁰

It would be fair to expect such a fundamental change in direction to have been informed by substantial supporting evidence, but that does not appear to be the case. Indeed, there remains much evidence that these conditions have what we would all consider psychological or psychiatric factors at their core, and little or no evidence to the contrary. The changes in approach appear to have been made largely in efforts to “destigmatize” these conditions; to define them as something other than psychiatric disorders. Although arguably well-meaning, we believe that this shift away from the psychological is short-sighted, and, most important, invalid. It hinders a clear understanding of these conditions in clinical settings and thus leads to poorer treatment outcomes. It misdirects research efforts, as we will discuss. And it is doomed to fail as it does not reflect the underlying nature of these disorders. As Feynman says, “Nature cannot be fooled”. ¹¹

In this CJP Perspective, we suggest that the DSM-5 agnostic stance has been of detriment to the functional disorder field, from the point of view of patients and clinicians, and in terms of research. We commence by presenting the psychological causation model, which in essence prevailed for more than a century before DSM-5.

The Psychological Causation Model

The psychological causation model of functional disorders proposes that these conditions occur when different forms of psychological or psychiatric distress are non-consciously and involuntarily expressed as physical symptoms and signs. The physical manifestations may appear to be the result of a general medical condition, but thorough assessment shows them to be “medically unexplained”.

The underlying psychological causes are heterogeneous, as any form of emotional distress may end up being expressed physically, including the dysphoria of psychiatric syndromes such as major depressive disorder or panic disorder; the chronic fluctuating emotional distress seen in some personality disorders; and the mental discomfort that occurs in response to emotional stressors. In addition, the route from underlying dysphoria to physical symptoms is also heterogeneous, with some being direct (e.g., anxiety-related palpitations repeatedly being misinterpreted as cardiac disease) and others indirect (distress from childhood trauma emerging as a gait disturbance). Functional symptoms, under this model, are seen to go some way to temporarily ameliorate the direct pain of psychological distress.

The form of the physical presentation is less important than the fact that a functional condition is present. In this model, the psychological component is primary: it is the engine driving the entire condition, rather than being a co-morbidity, or solely a reaction to physical symptoms. This model also suggests that prognosis will be determined more by the nature of the underlying psychological distress than by the severity of the physical manifestation. ¹²

There is considerable – albeit not definite – evidence that psychiatric/psychological engines drive functional conditions. This includes the very high rates of association of these syndromes with overt psychiatric conditions ⁸ and prior psychological trauma;^13,14 the fact that patterns of symptoms are often based on patient beliefs about body physiology; ¹⁵ persuasive clinical examples of “conversion” of mental distress into physical syndromes; ¹⁶ and the positive responses to psychological and psychiatric therapies when a somatization model is assumed. ¹⁷

The Currently Predominant Agnostic Causative Position

Since the publication of DSM-5, most published reviews and research papers on functional disorders have pushed aside the psychological causation model and adopted a predominantly agnostic stance, bringing a largely neurobiological lens to bear. Leaders in the field take care to describe functional conditions as changes in brain function of uncertain origin. They emphasize “brain network dysfunction”^18,19 and downplay or simply eschew psychological factors when defining functional neurological disorder (FND).

The FND Society, an international organization of clinicians and researchers, also supports an agnostic approach, while the EURONET-SOMA Group suggests that functional conditions “should occupy a neutral space within disease classifications, favouring neither somatic disease aetiology, nor mental disorder”. ²⁰

Patient support groups use agnostic definitions and at times actively argue against acceptance of psychological engines. The widely used online “FND guide” neurosymptoms.org makes no reference to psychological factors in its FND definition or homepage, and portrays them as “one of many risk factors for FND” in its discussion of “causes”. ²¹ FNDAction, a UK-based online patient support organization, cites a 2018 article, thus: “[FND] is often explained to patients as a psychological reaction due to past trauma, or as symptoms due to stress. These explanations usually fail and result in patients feeling alienated, stigmatised and not-believed. The main reason for the failure of such explanations is that they take a potential risk factor and turn it into the cause of the problem.” ²²

Many are seduced by what is presented as a novel and alluring way of understanding these conditions (e.g., “disorders of brain network dysfunction” ²³ or even “maladaptive changes in neural computation” ²⁴ ) without it being acknowledged that almost all conditions accepted as psychiatric can be framed in this fashion.

Semantics: “Rule-In”/“Positive” Good; “Unexplained”/“By Exclusion” Bad

In consort with the agnostic position, a great deal of emphasis is now placed on “rule-in” or “positive” signs in FND. ²⁵ These are signs such as split-vibration sense or “tunnel vision” that unequivocally denote a functional component to a clinical presentation. Proponents imply that this emphasis improves the veracity of these conditions: “(FND), previously regarded as a diagnosis of exclusion, is now a rule-in diagnosis with available treatments. This represents a major step toward destigmatizing the disorder, which was often doubted and deemed untreatable”. ¹⁹ Although useful, “rule-in” signs are not at all necessary for the diagnosis of functional disorders, which can reliably be made based on the entire clinical picture. The essence of a functional diagnosis is the detection of a constellation of symptoms and signs that do not follow the patterns of known general medical conditions, and where very thorough clinical assessment and investigation reveals no causative underlying general medical condition.

The exaggeration of the importance of “rule-in” signs is synchronous with the overall attempt to refurbish these conditions. A superficial semantic appeal seems to be at play, with terms such as “positive” and “rule-in” framing the conditions in a more upbeat and optimistic fashion than the now avoided terms “unexplained” and “by exclusion”. But “diagnosis by exclusion” thus gets an unfairly bad rap. After all, the concept has a long history of being useful in medicine, being indispensable for diagnoses as common as essential hypertension, and remains crucial when working to help individuals with functional conditions.

Pseudo-Destigmatization

When the change in nomenclature and the shift to agnosticism in DSM-5 was planned, a central declared motivation was that this would “destigmatize” these conditions. But we cannot “destigmatize” a condition by changing its name, redefining it, or by massaging its conceptualization such that it becomes something that it isn’t. This is sleight of hand; it is a “pseudo-destigmatization”, attempting to sanitize FND by rescuing it from its label as “psychiatric”. And what does this say about our stance regarding all people with mental health concerns?

To actually destigmatize a condition, we have to accept it for what it is, face this squarely, and then strongly advocate for the acceptance of the veracity of the condition and for the support of those whom it affects. This entails working to educate colleagues, patients, and society-at-large regarding the true nature of that condition. In functional disorders, this includes emphasizing that these conditions are as “real” as any other medical condition, that they are produced by non-conscious and involuntary mechanisms, that they can strike anyone in our society, that they do not represent malingering, and that they can be highly distressing and disabling. Furthermore, that people suffering these conditions require and deserve respect, and resources for their care.

Clinical Considerations: Always Challenging for Clinicians; a Large Untreated Burden of Suffering

Functional disorders have always presented formidable challenges to clinicians, who are at their most comfortable treating diseases that have apparently clear pathophysiologies that lead logically to treatment interventions. Functional presentations can be very complex, with myriad symptoms and signs, and lengthy histories. For clinicians to seek reassurance that they have excluded general medical causative factors to a reasonable degree of certainty can be daunting enough. Once that is achieved, other challenges unfold, largely conceptual. What is actually causing the symptoms? How do I explain fluctuations and apparent inconsistencies? How do I understand the fact that functional syndromes are non-consciously and involuntarily produced, yet follow each individual patient's cognitive understanding of how the body works and how they expect diseases to express themselves? ¹⁵ How do I differentiate this from malingering? What exactly would/should I be treating?

Without conceptual guidance and informed experience, many clinicians maintain lingering doubts about the veracity of these conditions, and consciously or unconsciously avoid working with, or are dismissive of, such patients. Being thwarted as a medical expert can lead doctors to resent such patients, and blame them for “wasting time and resources”. Even clinicians who are well equipped to help individuals with functional disorders can be daunted by the task, as providing the thorough assessment and the customized management each patient ideally requires is resource-intensive.

Thus, even though these conditions are very common, affecting up to 22% of patients in primary care settings, ²⁶ they remain under-diagnosed and under-treated. ² This occurs not simply because of ongoing stigmatization, nor because of any fundamental limitations in the older psychological model, but rather because of their inherent complexity, failed classification systems (with consequent lack of straightforward consensus understanding of the conditions), and limited clinical resources. Blurred understanding is likely a bigger hurdle for the field than the challenges of actually reducing stigma.

Do Clinicians Embracing the Agnostic Model Really Not See Functional Disorders as Primarily Psychological/Psychiatric Conditions?

All functional disorders are brain-based and are the product of brain function, and thus could, along with all complex conditions affecting human behaviour be accurately labelled “neuropsychiatric”. And at the same time, we submit that these conditions are fundamentally driven by what we would all agree to be best characterized as “psychiatric” or “psychological” distress. This observation is made not to foster a false dualism between neurology and psychiatry or between “brain” and “mind”, but rather to emphasize that the field would benefit from clinicians being clearer about the kind of neuropsychiatric distress that is driving these disorders. We are of the opinion that it is valid for clinicians to approach these conditions as primarily being driven by various types of dysphoria, rather than by the clinically nebulous “disorders of brain network dysfunction”. ²³

Indeed, clinicians and commentators who publicly champion the agnostic approach continue to: emphasize the need for psychiatric assessment for all patients; ¹⁰ recommend psychotherapies (e.g., cognitive behavioural therapy (CBT)) for most patients; and when medications are prescribed, they are invariably psychotropics. ²⁷ This is confusing, even disingenuous. Patients notice the apparent contradictions. The resultant puzzlement is well summed up in one of the “frequently asked questions” at a prominent US hospital's FND website: “If this is a brain problem, why are you recommending psychotherapy as treatment?” ²⁸

Implications for Management

The agnostic position also impedes treatment itself. How does one treat a “brain network dysfunction”? The position naturally results in a hesitant clinical approach: an oblique formulation, and then possibly a standardized CBT program with physical therapies that will help some patients but is not designed to understand the unique psychological underpinnings.

In contrast, the “psychological-engine” conceptualization allows clinicians to help patients in a straightforward yet flexible fashion. After a thorough assessment, the patient can be engaged in an individualized formulation and treatment plan that emphasizes: a strong therapeutic alliance; education about the nature of their disorder; treatment of underlying dysphoria as with any other patient (individually customized psychotherapy and pharmacotherapy); adding physical rehabilitation techniques if indicated; being a strong advocate for the patient; and accepting that successful treatment takes time and commitment.

In reality, clinicians worldwide continue to use the psychological model to good effect.^16,29–31 A recent survey showed that the majority of Italian psychiatrists still see “conversion” as a psychological phenomenon, yet the authors of this paper chastize them for this. ⁹ The World Health Organisation, in the 11th Revision of the International Classification of Diseases (ICD-11) considers the psychological mechanism underpinning FND to be dissociative (“involuntary disruption or discontinuity in the normal integration of motor, sensory or cognitive functions”), calls it “Dissociative Neurological Symptom Disorder” and places it in the Dissociative Disorders group. ³² As the ICD encompasses all human diseases, it had the capacity to also code FND in the Neurological section, acknowledging that neurologists make frequent use of the diagnosis, and that patients with FND are almost always “shared” between neurology and psychiatry. ³³

Effects of Agnosticism on Research on the Neurobiology of FND

Reading reviews of the current state of the understanding of the neurobiology of FND, one may be forgiven for concluding that great strides have been made in this area.^18,34 Most studies have been driven by hypotheses about abnormal functions leading to FND, and are designed to search for alterations in structure or function in the neurological centres and circuitry thought to underpin those functions. Ensuing results are held up as evidence for the characterization of FND at the neurobiological level, with claims such as: “evidence supports modeling FND as a multi-network brain disorder implicating alterations within and across limbic/salience, self-agency/multimodal integration, attentional, and sensorimotor circuits” with “roles for brain circuits implicated in motor conceptualization, inhibitory control, attention, predictive processing/perceptual inference, meta-cognition, belief/expectation, emotion control, and threat-related defense behaviours in the pathophysiology of FND”. ⁸

Such conclusions gloss over major methodological constraints. Importantly, almost every published study compared individuals with FND with healthy controls. This means that any described changes cannot be definitively associated with FND itself, as they may well be explained by more general confounding factors, such as anxiety or depression. Thus, these studies may simply be describing variations in brain function that are seen in various forms of psychiatric distress.^35–41 Comparison with individuals suffering common forms of psychological distress is required, such that the essence of FND itself can be determined.

There is thus an imperative to consider underlying psychological factors in all FND research, and to design studies keeping in mind the possible primacy of psychological factors. There has been some welcome recent discussion regarding the importance of using psychiatric control groups. ⁸ The results of research once general psychiatric controls are used may well be sobering, with many of the recently described apparent specific correlates of FND being lost when compared to those populations.

Furthermore, current research endeavours almost exclusively define subtypes at the level of physical presentation, whereas the psychological model suggests that the more valid phenotype will be defined at the level of the psychological/psychiatric engine. A welcome development in this regard is the consideration of a “trauma subtype” of FND,^13,42 and one can imagine this being usefully extended through to considerations of other psychological/psychiatric “subtypes”.

Functional conditions are all products of brain function, and consequently, we would expect that at some point in the distant future, they will be understood at a brain circuit and even molecular level. In the same way, we expect this will be the case with other complex neurobehavioral conditions such as post-traumatic stress disorder (PTSD), bipolar affective disorder, or schizophrenia. However, the current claims are premature, and are at risk of leading casual or uncritical observers to imagine that FNDs are now clearly defined as discrete pathophysiological entities.

Conclusions: A Call for a Return to an Understanding That Psychological/Psychiatric Distress is Central in FND

In sum, we contend that the DSM-5-inspired agnostic “renaissance” has been of benefit to neither clinicians nor patients and has led to a circularity in research. Many very well-meaning researchers are working hard to understand the neurobiological underpinnings of the functional disorders. We are very grateful for their work to this point, and look forward to them advancing the field over the coming decades. We respectfully suggest they will be far better served with work driven by a psychological/psychiatric engine model; one that evidence supports and no evidence refutes, and one borne out by more than a century of clinical experience. And we would strongly suggest that this position best benefits clinicians and patients. It allows for a clear understanding of a path to effective care, and to dealing with unfair stigmatization head-on.

The needs of patients with functional disorders are our central consideration. In most countries, health-care restraints are preventing them from obtaining optimal treatment, and they require strong advocacy for increased clinical resources. Now more than ever, the large population of individuals suffering functional conditions requires clarity of thought and purpose from their clinicians. We suggest that the late Zbigniew Lipowski got it right when he said: “If no disease is found, the patient needs to be told so in unambiguous terms, and the focus of the inquiry should shift to the issue of psychiatric diagnosis … as this will require appropriate treatment”. ⁴³