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Nine Specialists Challenge the Conflation of POTS, Dysautonomia and FND

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What happens when a patient has dizziness, tremors, weakness, fatigue, exercise intolerance and a racing heart? Do doctors investigate the autonomic nervous system, or do they decide the symptoms are functional? The distinction is hardly academic. One approach may identify measurable cardiovascular abnormalities and lead to targeted treatment. The other may send the patient down an entirely different therapeutic pathway, potentially without addressing the underlying problem.

In November 2024, nine medical specialists, including neurologists, cardiologists and autonomic disorder experts, published an unusually direct opinion paper in Frontiers in Neurology: Postural orthostatic tachycardia syndrome and other common autonomic disorders are not functional neurologic disorders. Led by Svetlana Blitshteyn, with coauthors including Blair Grubb, Glenn Treisman and Brent Goodman, the paper challenges attempts to associate established autonomic diseases with Functional Neurological Disorder (FND) without adequate diagnostic justification.

The authors are not merely arguing over terminology. They identify differences in diagnostic criteria, underlying mechanisms and treatment, question assumptions about comorbidity, and warn that patients with autonomic disorders can be misdiagnosed with FND. Most importantly, they describe how an existing FND diagnosis can interfere with subsequent medical care. Their concern is that patients may receive treatment for a presumed functional disorder while physiological abnormalities remain insufficiently investigated.


These disorders have their own diagnostic criteria

Postural orthostatic tachycardia syndrome (POTS) is characterised by orthostatic intolerance and an excessive increase in heart rate upon standing. In adults, the diagnostic threshold includes a sustained heart-rate increase of at least 30 beats per minute within ten minutes of standing, without significant orthostatic hypotension, alongside chronic orthostatic symptoms and exclusion of alternative explanations. Adolescents have a higher threshold of 40 beats per minute. Other autonomic disorders, including orthostatic hypotension, inappropriate sinus tachycardia and neurocardiogenic syncope, have their own diagnostic requirements.

These are not simply collections of vague symptoms. Clinicians can assess heart rate, blood pressure and responses to standing through appropriate investigations, including active standing assessments and tilt-table testing. FND, by contrast, is diagnosed through clinical findings interpreted as evidence of incompatibility with recognised neurological or medical conditions. Its diagnostic criteria do not establish POTS, orthostatic hypotension or other cardiovascular autonomic disorders.

The distinction is fundamental. A patient can have fatigue, dizziness, shaking and weakness without those symptoms revealing their underlying cause. The fact that a presentation appears unusual, variable or difficult to explain does not establish that an autonomic disorder is absent. Nor does a normal brain MRI or EEG tell clinicians whether the patient's cardiovascular autonomic regulation is functioning correctly.

Established autonomic diagnostic criteria are described in the Heart Rhythm Society expert consensus statement and the 2022 review of POTS diagnosis and management.


Where is the evidence that POTS and FND commonly coexist?

One of the paper's most interesting arguments concerns comorbidity. The authors examined findings from three previously published POTS studies involving a combined 5,214 patients. FND was not identified as a common comorbidity in these datasets. By comparison, conditions such as migraine, gastrointestinal disorders, small-fibre neuropathy, hypermobility syndromes and autoimmune diseases were frequently reported.

They also examined a separate survey involving 526 people with FND. Only ten participants reported POTS diagnoses, representing approximately 1.9% of respondents. Three had been diagnosed with POTS before FND, while seven received a POTS diagnosis afterwards. The authors note that this made POTS one of the least frequently reported comorbidities in that particular survey.

There is an important limitation: none of these studies was specifically designed to establish the true prevalence of FND among patients with POTS, or vice versa. The findings therefore cannot prove that the conditions never coexist. But they also do not establish that FND is a common POTS comorbidity. The authors explicitly call for research using appropriate diagnostic criteria and suitable comparison groups.

That distinction matters whenever a clinician retains an FND diagnosis after discovering an autonomic disorder. Coexistence is possible, but it is a claim requiring evidence. Simply retaining the original diagnosis does not establish that two independent disorders are present. If the newly identified condition plausibly explains the symptoms originally attributed to FND, the earlier diagnostic reasoning deserves reassessment.

Interestingly, the FND survey cited by Blitshteyn and colleagues was coauthored by Kim Hearne, Mark Edwards and others. The survey is Functional neurological disorder: clinical manifestations and comorbidities; an online survey, published in 2023. Its reported POTS figures are part of the evidence discussed in the 2024 paper, not evidence of a widespread POTS–FND overlap.


When the diagnosis becomes an obstacle to further investigation

The paper goes beyond disagreements about classification. The authors report that, in their clinical experience, patients with autonomic disorders, including post-COVID dysautonomia and infection-associated chronic illnesses, are frequently misdiagnosed with FND. They describe a particularly troubling consequence: once FND enters the medical record, subsequent complaints may be attributed to that diagnosis, making further investigation and treatment harder to obtain.

"Once diagnosed with FND, patients often have difficulty obtaining further diagnostic and therapeutic care"

Blitshteyn et al., 2024

This is diagnostic overshadowing, and its consequences can be serious. A patient reporting new weakness, fainting, abnormal heart-rate changes or deteriorating exercise tolerance may require investigation of those symptoms regardless of previous diagnoses. If clinicians treat the existing FND label as a sufficient explanation, potentially identifiable abnormalities may go unrecognised.

The authors' warning is based partly on their clinical experience rather than a prospective study measuring the frequency of these diagnostic errors. That limitation matters, but it does not make the concern irrelevant. The question is whether clinicians are adequately investigating symptoms before assigning them to a functional diagnosis, and whether they remain willing to reconsider that diagnosis when contradictory evidence appears.

FND Nope has previously examined cases illustrating these concerns, including two women initially diagnosed with FND whose subsequent investigations identified POTS, and 17 patients diagnosed with psychogenic seizures who were later found to have autonomic abnormalities. These cases do not establish the population-wide frequency of misdiagnosis, but they demonstrate why further physiological investigation can change the clinical picture.


The wrong treatment is not a harmless administrative mistake

Perhaps the most consequential part of the paper concerns treatment. POTS and other autonomic disorders may require fluid and salt supplementation, compression garments, medications affecting heart rate or vascular regulation, and exercise programmes adapted to the patient's physiological limitations. Treatment depends on the particular diagnosis and the patient's clinical circumstances.

The authors contrast these approaches with FND-oriented psychotherapy and physical rehabilitation. Their concern is that treatment programmes developed for presumed functional symptoms may be inappropriate when the patient's limitations arise from autonomic dysfunction or associated conditions such as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and hypermobility spectrum disorders.

Exercise intolerance is a recognised feature of POTS. Some patients cannot tolerate prolonged upright activity and may require recumbent or supine exercise, with carefully adjusted intensity. Patients with ME/CFS may experience post-exertional malaise, in which exertion causes a disproportionate worsening of symptoms. Applying an unsuitable exercise programme without recognising these limitations can aggravate the patient's condition.

Blitshteyn and colleagues therefore argue against uniformly prescribing FND-targeted exercise to patients with autonomic disorders. Even when a patient independently meets diagnostic criteria for both POTS and FND, they recommend treating POTS first before proceeding with FND-specific interventions.

There is nothing particularly mysterious about this principle. If a patient has an identifiable physiological disorder with established treatment options, that disorder should be addressed. A diagnostic label is not a substitute for treatment, and rehabilitation is not automatically appropriate simply because a clinician has described the symptoms as functional.


What the paper establishes, and what remains unanswered

This publication is a peer-reviewed opinion article, not a new clinical trial or systematic review. It draws on established diagnostic criteria, previously published research and the authors' clinical experience. It does not establish the precise frequency of POTS being misdiagnosed as FND, prove that the conditions can never coexist, or demonstrate that every unusual movement in a patient with autonomic dysfunction is caused by that dysfunction.

Those limitations should not be confused with a lack of substance. The distinction between measurable autonomic abnormalities and clinical findings used to diagnose FND is real. The treatments are different. The potential consequences of choosing an inappropriate diagnostic pathway are real. And the available studies cited by the authors do not justify assuming that FND is a common comorbidity of POTS.

The paper also raises a broader question relevant to the Common Phenotypes Hypothesis. If similar neurological presentations can arise from different underlying disturbances, how confidently can clinicians classify those presentations before identifying their causes? Recognising a pattern is not the same as establishing its mechanism. The 2024 paper does not test that hypothesis, but its insistence on distinguishing symptoms, diagnoses and underlying physiology illustrates why the question matters.

There is a tendency in diagnostic discussions to treat an existing label as settled unless someone can conclusively disprove it. That reverses the responsibility of diagnosis. If a patient is subsequently found to have POTS, small-fibre neuropathy, an autoimmune disorder or another condition capable of producing the relevant symptoms, the original reasoning should be reconsidered. Calling the new finding a comorbidity may be justified in some cases, but it cannot simply be assumed.

A diagnosis should explain the evidence, not become a reason to stop looking at it. If measurable autonomic dysfunction is discovered after symptoms were labelled functional, the sensible response is to investigate what that finding explains, not automatically preserve the original label.

The central warning from these nine specialists is straightforward: POTS and other established autonomic disorders are not FND. Their diagnostic criteria, proposed mechanisms and treatment requirements differ substantially. Conflating them risks sending patients down the wrong clinical pathway, particularly when an existing FND diagnosis discourages further investigation.

Medicine does not become more scientific by forcing poorly understood symptoms into a convenient category. It becomes more scientific by testing explanations against evidence, recognising uncertainty and changing course when new findings demand it. For patients whose autonomic abnormalities have been overlooked, that distinction can determine whether they receive appropriate treatment or remain trapped behind a diagnosis that was never adequately reconsidered.


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