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Dismantling FND: When ME/CFS Starts Trespassing on Functional Neurology's Territory

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Functional Neurological Disorder (FND) may have a territorial problem. For decades, unexplained weakness, tremors, sensory disturbances, seizure-like episodes, and other unusual neurological symptoms have been fertile ground for functional and psychogenic diagnoses. Then along comes research into ME/CFS, dysautonomia, small-fiber neuropathy, and related conditions, investigating physiological mechanisms capable of producing some of those very same symptoms. Suddenly, what looked like a functional neurological problem to one clinician may look like an incompletely investigated physiological illness to another. The symptoms haven't changed. The available explanations have. Awkward.

And now two healthcare professionals are openly discussing dismantling FND as a diagnostic construct. Not improving its public relations, not producing another leaflet about malfunctioning brain software, and not finding a more reassuring way to explain why patients supposedly need to retrain their nervous systems. Dismantling it.

In a presentation featuring Dr. Brayden Yellman, a physician treating ME/CFS and associated chronic illnesses, and Paige Zuckerman, M.Ed., of Beehive Mental Health, the speakers challenge the diagnostic assumptions surrounding FND and describe how physiological illness can be misinterpreted as psychiatric or functional dysfunction. Their discussion includes autonomic abnormalities, post-exertional malaise (PEM), neuroinflammation, mast cell activation, and patients whose original diagnoses failed to adequately account for their clinical presentations.

When Two Diagnoses Start Fighting Over the Same Symptoms

The potential conflict between FND and ME/CFS goes considerably deeper than two groups of specialists disagreeing about terminology. It concerns the interpretation of symptoms, the evidence considered sufficient to establish a diagnosis, and the consequences when that interpretation is wrong. Historically, conversion disorder and other functional diagnoses have been applied to neurological symptoms that appeared inconsistent with established medical explanations. ME/CFS and its associated conditions, meanwhile, are the subject of ongoing research into physiological abnormalities that can produce symptoms which are difficult to explain through routine neurological investigations.

Consider tremors, weakness, sensory disturbances, dizziness, speech difficulties, and seizure-like episodes. These symptoms can appear in discussions of FND, but they can also occur in patients with dysautonomia, orthostatic intolerance, neuropathy, and other medical conditions. The presence of an unusual symptom does not establish which mechanism is responsible. Yet the consequences of choosing the wrong explanation can be substantial, particularly when that explanation determines which investigations are performed, which treatments are offered, and whether further medical concerns are taken seriously.

This is where the territorial dispute becomes interesting. As researchers identify additional physiological abnormalities and mechanisms associated with complex chronic illnesses, some symptoms previously considered medically inexplicable may become more understandable. That does not mean every FND diagnosis is automatically disproved, but it does mean that diagnostic confidence should be proportionate to the evidence. Medicine cannot reasonably treat its current understanding as the final inventory of what the human body is capable of doing. Unfortunately, the human body has never shown much respect for the limits of a clinician's training.

There is also a direct treatment conflict. Some FND rehabilitation approaches involve progressively restoring activity and movement, while patients with ME/CFS may experience post-exertional malaise, a worsening of symptoms following physical, cognitive, or other exertion. The NICE guideline for ME/CFS explicitly advises against fixed-increment graded exercise therapy. Applying an inappropriate activity-increasing programme to somebody with unrecognized PEM can therefore have consequences considerably more serious than an academic disagreement about diagnostic labels.

In other words, this is not simply a question of who gets to claim the weird symptoms. It is a question of what happens when the wrong diagnostic framework determines the patient's care.


Dismantling FND, Not Just Giving It Another Name

At approximately 39:26, Zuckerman makes her position remarkably clear:

"We are both really interested in the notion of dismantling functional neurologic disorder."

She describes contributing to that effort as a goal for the remainder of her career. Her criticism concerns the historical relationship between FND and conversion disorder, arguing that the change in terminology has been largely semantic and that psychogenic assumptions continue to influence clinical practice. The diagnosis has acquired a new name, but she questions whether the thinking behind it has undergone anything resembling the same transformation.

She also challenges the use of graded exercise and psychologically directed interventions in patients who may have unrecognized PEM. If a patient has a physiological limitation that worsens with exertion, interpreting that limitation as a psychological barrier to overcome is not a particularly promising starting point. The patient may be told to push through symptoms when the relevant medical advice would be to manage activity within their individual limits. Nothing says precision medicine quite like treating two potentially different problems as though they were interchangeable.


Five Patients, Four Subsequent Diagnoses

At approximately 41:20, Zuckerman describes five clients who had received conversion disorder or FND diagnoses. Four subsequently received diagnoses within the hypermobile Ehlers-Danlos syndrome (hEDS), postural orthostatic tachycardia syndrome (POTS), mast cell activation syndrome (MCAS), or ME/CFS spectrum.

That is four out of five in her personal clinical experience. It is not a controlled study, and the presentation does not establish whether the original diagnoses were formally withdrawn or whether the later diagnoses were considered coexisting conditions. Nevertheless, it raises an obvious question: how thoroughly were these patients investigated before the functional labels were applied, and what would have happened if nobody had questioned those labels?

A diagnosis can become remarkably durable once it enters a medical record. Subsequent clinicians may encounter the label before they encounter the patient, and symptoms can be interpreted through an existing diagnostic framework rather than assessed independently. The patient may continue deteriorating, but at least the paperwork has achieved stability.


Incompatible With Recognized Disease. Recognized by Whom?

Perhaps the sharpest criticism comes from Yellman's examination of the diagnostic criteria for FND, beginning around 43:15. The criteria require clinical findings demonstrating incompatibility between the symptoms and recognized neurological or medical conditions.

Yellman's response is beautifully economical:

"Well, what if you don't recognize them?"

There it is. An entire diagnostic problem packed into one question.

Medicine is not an inventory of every possible disease mechanism, and an individual clinician is certainly not an inventory of everything medicine already knows. A physician unfamiliar with dysautonomia, small-fiber neuropathy, ME/CFS, or other relevant disorders may fail to recognize a physiological explanation that another specialist would investigate. The patient's biology does not become functional simply because the clinician's knowledge has reached its destination.

Yellman points to weakness, tremors, gait abnormalities, swallowing difficulties, speech problems, seizure-like episodes, and sensory disturbances as examples of symptoms that may arise in the chronic illness populations he treats. His argument is not that every patient with these symptoms has the same disease, but that the symptoms themselves cannot establish a functional explanation without adequate clinical reasoning.

And this is where the supposed elegance of diagnostic incompatibility becomes rather less elegant. If the clinician has not considered the relevant physiological possibilities, what exactly has been demonstrated to be incompatible? The disease, or the clinician's understanding of it?


The Pseudoseizures That Apparently Had Other Plans

Earlier in the presentation, at approximately 11:27, Yellman describes a patient diagnosed with psychogenic nonepileptic seizures (PNES). During a passive standing test designed to investigate orthostatic intolerance, the patient reportedly developed significant cardiovascular abnormalities followed by the same rhythmic tremors and seizure-like symptoms previously experienced at home.

The test had to be stopped, the patient was lowered to the floor, and intravenous saline was administered. Yellman reports that following more aggressive treatment for orthostatic intolerance, the patient experienced no further episodes.

That is a clinical anecdote, not proof that PNES generally results from orthostatic intolerance. But it raises an important question about the original diagnosis. If a physiological challenge can reproduce the supposedly psychogenic episode, and treatment directed at the identified physiological abnormality is followed by its disappearance, perhaps that mechanism deserved investigation before the psychiatric explanation became established.

It is rather inconvenient when the patient's cardiovascular system refuses to cooperate with the psychological narrative.


When Strange Symptoms Become Evidence Against the Patient

Near the conclusion, Yellman describes another familiar clinical problem: the tendency to interpret unusual symptoms as evidence of psychiatric disturbance rather than as reasons to investigate further. At approximately 1:03:45, he characterizes the faulty reasoning as follows:

"A crazy symptom equals a crazy person."

He is criticizing that reasoning, not endorsing it. His examples include extraordinary medication reactions and severe sensory responses to ordinary environmental stimuli. Rather than concentrating on whichever symptom sounds most ridiculous, he argues that clinicians should examine the complete clinical picture, including orthostatic intolerance, vestibular abnormalities, autonomic dysfunction, and other systemic findings.

This matters because unusual symptoms can become a credibility test that the patient never agreed to take. Describe something familiar and the clinician may investigate it. Describe something sufficiently unusual and suddenly the conversation can drift toward psychological explanations. Apparently, the more complicated the patient's physiology becomes, the more tempting it is to simplify the patient instead.


Why Not Actually Test the Treatment Model?

At approximately 1:06:40, Yellman proposes a comparative study involving patients diagnosed with FND. One group would receive conventional FND-directed treatment, while another would undergo screening for post-exertional malaise and orthostatic intolerance, receive pacing education, and be offered basic physiological support where indicated.

The outcomes would then be compared and published in psychiatric literature. Yellman even remarks that he believes he knows what the results would be before conducting the study. That prediction is not evidence, of course, but the research question is entirely legitimate: how many patients assigned an FND diagnosis might benefit from systematic investigation and management of physiological abnormalities that were previously overlooked?

It would also be interesting to establish how often those abnormalities are identified, whether their treatment changes the presenting neurological symptoms, and whether outcomes differ from those achieved through existing treatment pathways. Those are measurable questions. They do not require an inspirational metaphor about faulty brain software, just a properly designed study.


The Bigger Problem

Beyond the explicit criticism of FND, the presentation repeatedly returns to the consequences of psychiatric labeling in complex chronic illness. Yellman discusses autonomic symptoms mistaken for anxiety, neurological symptoms occurring during orthostatic stress, and neuropsychiatric presentations potentially influenced by immune and metabolic dysfunction. Some of the proposed mechanisms remain under investigation, and the clinical anecdotes cannot establish their general prevalence. But the broader concern is clear: when physiological illness produces symptoms that resemble psychiatric conditions, the resemblance itself is not an explanation.

The speakers also discuss the isolation, loss of independence, medical mistrust, and psychological distress experienced by people with severe chronic illness. Their argument is that clinicians must distinguish the consequences of living with disabling symptoms from assumptions about what originally caused those symptoms. Being distressed by an illness does not establish that distress caused the illness. That should be obvious, but apparently obvious things sometimes require an entire medical conference presentation.

What makes this discussion significant is not that two professionals have disproved FND. They have not. It is that they are publicly challenging the confidence with which functional explanations can be applied, describing clinical experiences that warrant further investigation, and calling for comparative research rather than simply accepting the existing diagnostic framework.

There is a particularly uncomfortable possibility here: some patients may spend years being treated for a functional disorder while clinically relevant physiological abnormalities remain unidentified or inadequately addressed. The presentation does not establish how frequently that happens, but its examples make the question difficult to dismiss.

And perhaps that is the question worth asking every time a patient with unexplained neurological symptoms receives a confident functional diagnosis: have we established what is happening to this patient, or have we simply established the limits of what we bothered to investigate?

Because those are two very different achievements, and only one of them deserves to be called a diagnosis.

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