Dysautonomia as a Differential Diagnosis for PNES: What 17 Misdiagnosed Patients Show
FND Nope
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A 2026 study published in Frontiers in Neurology examined 17 patients who presented with seizure-like movements, had no corresponding epileptiform activity on EEG, and had previously been diagnosed with psychogenic non-epileptic spells (PNES). The researchers subsequently identified autonomic abnormalities in these patients and described their earlier functional neurological disorder (FND) diagnoses as misdiagnoses.
“Inclusion criteria required non epileptiform movements, confirmed by negative rEEG or cEEG testing, followed by a misdiagnosis of a functional neurological disorder...”
The earlier Movement Disorder Society abstract was even more specific, describing the inclusion criterion as a “misdiagnosis of PNES”. This distinction matters because the investigators were not simply reporting autonomic abnormalities in patients with established FND. They were examining patients whose previous diagnoses they considered incorrect.
All 17 patients had orthostatic abnormalities, including orthostatic hypotension or postural tachycardia, suggesting autonomic dysfunction. The authors propose the term Autonomic Movement Disorder (AMD) for abnormal movements associated with autonomic disturbances and impaired cerebral perfusion. This is a proposed clinical classification rather than an independently validated diagnostic category.
Why dysautonomia matters in the differential
Dysautonomia can produce symptoms that overlap with presentations diagnosed as PNES or other forms of FND, including tremor, shaking, jerking or myoclonic movements, weakness, dizziness, altered responsiveness, presyncope and syncope. Some patients may also experience convulsive movements associated with cerebral hypoperfusion. Symptoms can fluctuate with posture, exertion, heat and other physiological triggers, potentially creating a clinical presentation that resembles a functional disorder.
A seizure-like event associated with autonomic dysfunction may therefore be mistaken for PNES, particularly when EEG shows no epileptiform activity. However, a negative EEG does not establish PNES as the cause. Its interpretation depends on whether a typical event was captured and whether the recording was adequate. Even when epilepsy is reasonably excluded, the cause of the event remains a separate diagnostic question.
The authors specifically recommend considering autonomic investigation before an FND diagnosis in relevant presentations:
“This suggests that in the presence of a negative EEG result and symptoms resembling a seizure, performing a tilt table test and checking orthostatic vitals prior to FND diagnosis can prove to be very useful...”
Orthostatic vital signs and tilt-table testing can help identify physiological abnormalities that might otherwise be overlooked. An abnormal result does not automatically establish the cause of every movement or episode, but it provides evidence that must be considered when evaluating the original diagnosis. The full paper is available here.
What happened to these patients?
The study describes patients who experienced repeated medical presentations before receiving appropriate neurological assessment. Some reportedly attended the emergency department as many as seven times before referral. This raises questions about whether their earlier diagnoses influenced subsequent investigations and how long potentially treatable autonomic abnormalities remained unidentified.
The individual cases are also revealing. The researchers describe patients presenting with convulsive syncope, shaking, dizziness, falls and transient unresponsiveness. One 19-year-old woman had leg shaking, dizziness and frequent falls, alongside a previously established diagnosis of postural orthostatic tachycardia syndrome (POTS). Her inclusion raises a particularly relevant question: how was the relationship between her known autonomic disorder and her seizure-like symptoms evaluated when PNES was diagnosed?
The paper does not provide sufficient detail to reconstruct every earlier diagnostic decision. Nevertheless, these cases illustrate why identifying an alternative disorder should prompt a review of which symptoms it can explain, particularly when that disorder was already known or could have been investigated using established autonomic testing.
Treatment outcomes and methodological limitations
Fourteen of the 17 patients were started on pharmacological treatment directed at autonomic dysfunction. Figure 2 in the paper reports improvement in 10 of those 14 patients, including improvement or resolution of abnormal movements and autonomic symptoms, alongside fewer hospital readmissions.
The reported outcomes are encouraging, particularly because treatment was directed at physiological abnormalities identified during investigation. However, the study is small, retrospective and uncontrolled. Without a comparison group, it cannot establish how much of the reported improvement was attributable to treatment, and improvement alone cannot prove that every previous PNES diagnosis was incorrect.
There are also inconsistencies in the reporting. The abstract refers to “10 of 17 patients who underwent pharmacological interventions”, despite stating that only 14 received medication. Figure 2 explicitly reports “ten of fourteen patients reporting improvement”, while the individual entries in Table 1 appear to identify 11 patients with reported improvement. These discrepancies make the precise outcome figures less certain. We retain 10 of 14 because that is the figure explicitly reported in Figure 2, while acknowledging the inconsistency.
Six patients were also lost to follow-up, limiting the completeness of the outcome data. The study cannot establish how frequently PNES is misdiagnosed in the wider patient population, nor does it validate AMD as a distinct diagnostic category. Its contribution is narrower: it documents a selected group of patients in whom autonomic abnormalities were identified after previous PNES/FND diagnoses, and whose investigators considered those earlier diagnoses to have been incorrect.
Coexistence is not evidence of coexistence
We originally came across this study through the following post by @dysclinic on X:
An online response to the original post included this observation:
“Even the authors acknowledge FND and dysautonomia aren’t necessarily mutually exclusive. Awkward.”
The authors do acknowledge that FND and autonomic dysfunction can coexist. What the paper does not demonstrate is that coexistence was established in these 17 patients. Instead, the investigators explicitly describe their previous FND diagnoses as misdiagnoses. Pointing out that two conditions are not mutually exclusive does not address whether both diagnoses were independently supported in the patients being studied.
Almost any two diagnoses can theoretically coexist. The relevant question is whether there is sufficient evidence for both in the individual patient. If dysautonomia is subsequently identified and can account for symptoms previously attributed to FND, the original attribution requires reconsideration. Simply adding dysautonomia to the existing diagnosis does not establish that the original diagnosis remains correct.
This is where diagnostic overshadowing becomes relevant. Once FND has been diagnosed, subsequent abnormalities may be interpreted as additional conditions rather than evidence requiring revision of the earlier explanation. The possibility of coexistence can then become a convenient way of retaining the original diagnosis, even when the newly identified disorder offers a plausible explanation for the symptoms that originally justified it.
There is an important distinction between demonstrating coexistence and merely asserting that coexistence remains possible. The former requires evidence for both conditions. The latter establishes very little. In these cases, the investigators identified autonomic abnormalities and considered the earlier PNES/FND diagnoses incorrect. A response based solely on the theoretical possibility of coexistence does not engage with that conclusion or establish that the original diagnoses were justified.
The problem of diagnostic revision
This raises a broader concern about the epistemic standards applied to FND. If the diagnosis can be retained whenever an alternative disorder is discovered simply because coexistence remains theoretically possible, it becomes difficult to establish what subsequent evidence would justify withdrawing it. A diagnosis that cannot be meaningfully reconsidered in light of new findings risks becoming resistant to correction.
The question is not whether coexistence is medically possible. It is what independent evidence remains for FND after the alternative disorder and its explanatory scope have been evaluated. Were the original symptoms genuinely supported by positive evidence for FND, or was the diagnosis reached because another explanation had not yet been identified? Those are different diagnostic circumstances, and discovering an autonomic disorder may have very different implications for each.
There is also a question for FND advocacy. In emphasising that FND can coexist with other neurological disorders, is insufficient attention sometimes given to circumstances in which the original diagnosis should be withdrawn? The possibility of coexistence is clinically relevant, but it should not become a reason to preserve an earlier attribution without examining whether the evidence supporting it still holds.
For these 17 patients, the investigators considered the earlier PNES/FND diagnoses to have been misdiagnoses. Their findings do not establish that every autonomic abnormality caused every reported movement, nor do they establish how often similar diagnostic errors occur. They do, however, provide a concrete reason to investigate dysautonomia in relevant seizure-like presentations and to reconsider an existing diagnosis when subsequent evidence offers an alternative explanation.
Ultimately, the issue is not whether FND and dysautonomia can coexist. It is whether the original diagnosis was adequately supported, whether autonomic dysfunction was appropriately investigated, and whether new findings prompted a meaningful reassessment. If an alternative disorder can account for the symptoms previously attributed to FND, what independent evidence remains for retaining the original diagnosis?
Sources
Khoo A, Paul M, Rady N, Sunda M, Brik J, Vaou O, Hohler A. Improved outcomes for patients with autonomic movement disorders originally evaluated for psychogenic non epileptiform spells. Frontiers in Neurology. 2026;17:1839185. Read the full paper.
Movement Disorder Society 2025 International Congress. Improved Outcomes for Patients with Autonomic Movement Disorders (AMD) Originally Evaluated for Psychogenic Non Epileptiform Spells (PNES). Read the original abstract.
There is a certain irony in KimH's criticism. By questioning how the researchers established misdiagnosis, she inadvertently raises the falsifiability problem surrounding FND itself. What evidence would actually be sufficient to overturn the original PNES diagnoses?
If identifying an autonomic disorder capable of explaining the presenting symptoms is insufficient because the conditions can coexist, and improvement following treatment of that disorder is also insufficient, what remains that could count against the original attribution?
Neither finding necessarily disproves PNES in isolation. But repeatedly invoking possible comorbidity without establishing independent evidence for both diagnoses risks making the original diagnosis resistant to revision. Every alternative explanation can simply be accommodated alongside it.
KimH is right to demand evidence for the researchers' classification of misdiagnosis. The difficulty is that her argument does not apply the same scrutiny to the original PNES diagnoses. In doing so, she risks illustrating the very problem she appears to be challenging: a diagnostic framework in which evidence is required to overturn FND, but the evidence required to retain it receives considerably less attention.
The question is not whether coexistence is possible. It is what evidence would justify withdrawing the original diagnosis, and whether that standard is being applied consistently.