Long Covid is not a functional neurological disorder

LLong Covid, the name given to cases of prolonged symptoms after an acute attack of Covid-19, is an umbrella diagnosis that covers a wide range of clinical manifestations and abnormal biological processes. Researchers have not yet identified a single or determining cause for some of the most disabling symptoms associated with long Covid, which are similar to those commonly observed in other post-acute infection syndromes. These include intense fatigue, post-exertional malaise, cognitive deficits (often called brain fog), and extreme dizziness.

Given current gaps in knowledge, some neurologists, psychiatrists and other clinicians in the United States, the United Kingdom and elsewhere have suggested that an existing diagnosis known as functional neurological disorder (FND) may offer the best explanation for many cases of this devastating disease.

We strongly disagree. While prominent outlets such as The New Republic and Slate have promoted this perspective, it is misguided to frame long Covid as a functional neurological disorder. Despite claims of strong evidence from those most invested in its promotion, the concept of FND rests largely on speculation and conjecture. Effective treatments for long Covid are far more likely to emerge from investigations of the kinds of immunological, neurological, hormonal, and vascular differences that have already been documented than from the inappropriate imposition of an often-inappropriate diagnosis on the vast swath of people with these prolonged symptoms.

Functional neurological disorder carries a lot of historical baggage. It’s the updated name for the old Freudian diagnosis of conversion disorder, in which people supposedly “convert” psychological trauma into physical disorders such as paralysis of the arms or legs. (Not long ago, some people with these disorders—especially women—would have been diagnosed as hysterical.) Over the past two decades, clinicians have tried to rename conversion disorder, recognizing that their patients often resent being told that their symptoms are psychosomatic.

In 2013, the psychiatric Diagnostic and Statistical Manual of Mental Disorders officially adopted the more neutral term “symptomatic neurological functional disorder” as an alternative name for conversion disorder. (In practice, the word “symptom” is generally dropped.) This update was accompanied by new diagnostic criteria. In addition to the lack of a better explanation of symptoms, a diagnosis of neurological functional disorder now also requires the presence of positive clinical signs considered incompatible with recognized neurological and other medical disorders, such as physical reflexes in an apparently paralyzed limb.

Today, neurologists and other experts frequently describe FND as a “brain network” disorder, with symptoms believed to be rooted in disruptions in the “the predictive machinery of the brain”, Personality disorders, misperceptions of autonomy, and hypersensitivity to bodily sensations, among other factors, are also described as a problem exclusively related to the brain’s “software” (how it works) rather than its “hardware” (or structural elements). The place of biological changes at the cellular, intracellular, or extracellular levels (such as possible alterations of mitochondria or epigenetic profiles) in this picture, or if they are at all, remains extremely unclear.

With this in mind, recommended treatments for FND include forms of psychotherapy and physical therapy specifically designed to address suspected problems with the brain’s “feedback mechanism” or “software.” Some people diagnosed with FND report improvement, with or without treatment. For many, the prognosis is poor.

Many people experience troubling symptoms that are not easily explained. Health professionals have known this all along, but the pandemic and the parallel wave of prolonged illnesses post-Covid-19 have heightened public awareness of the phenomenon. People with such symptoms, whether or not they are related to long Covid, are often dismissed and neglected by the medical system and doctors. A diagnosis of FND by a compassionate health professional can be a source of relief for many.

Yet many people with long Covid or prolonged symptoms from other causes reject the diagnosis of FND or complain that it was given to them after a cursory examination. Many find it can be difficult or impossible to have the diagnosis removed from their medical records.

Depression, anxiety, and associated mood disorders, which have become more prevalent during the pandemic, may obviously play a role in triggering and exacerbating symptoms. And in the case of long Covid, these neuropsychiatric features may themselves be rooted in immunological or biological aspects of the disease. In any case, like conversion disorder before it, conversion disorder as it is currently formulated and as it applies to people with long Covid is essentially impossible to prove or disprove.

Brain imaging studies show that people with and without FND differ in their patterns of brain activity—or “software,” as FND proponents like to call them. But these studies document associations, not cause-and-effect relationships. Research has also revealed differences in brain structures—what we would call “hardware”—between people with and without FND. What all these brain imaging findings mean remains unclear and open to interpretation.

In 2013, the renaming of conversion disorder to functional neurological disorder brought attention to a problem: the lack of reliable evidence that the new clinical signs required for functional neurological disorder accurately identify the condition. As a 2014 study noted, “These positive signs are well known to all trained neurologists, but their validity remains unclear.” Here is our translation of that statement: “All neurologists are trained to associate certain clinical signs with conversion disorder or functional neurological disorder, but this association cannot be supported by data.” Not much has changed since then.

Positive clinical signs represent an apparent discrepancy between an individual’s symptoms—whether or not they are related to long Covid—and the body’s normal behavior. But this discrepancy does not indicate that the symptoms are caused by problems with the brain’s “feedback mechanism,” misperceptions of autonomy, or the other hypothesized mechanisms of FND. These unproven explanations are best interpreted as fanciful ways of saying—or avoiding saying—“we really don’t know.”

Even before the COVID-19 pandemic, functional neurological disorders had entered a phase marked by a phenomenon known as diagnostic drift. Neurology articles routinely declared functional neurological disorders to be “common.” The FND Guide website, a popular resource for patients and clinicians, highlights the recent broadening of the diagnosis to include “vertigo” and “cognitive problems.”

These emerging FND subtypes seem particularly poised for growth in the age of coronavirus. Many people with long Covid experience dizziness, which is often clearly linked to autonomic nervous system problems. Many also experience profound cognitive changes, such as an inability to concentrate and frequent memory loss, which are clearly linked to factors such as changes in blood supply to the brain and neuroinflammation.

However, it is mainly the proponents of FND who insist that the broad areas of “dizziness” and “cognitive symptoms” fall within their purview. Other scientists and clinicians reject the categorization of these and other complex manifestations of long Covid as forms of FND and are looking at pathobiological processes for answers. A recent study published in the journal Nature, for example, reported a link between greater cognitive symptoms in long Covid patients and higher levels of a biomarker also present in many neurodegenerative diseases.

The FND literature cautions clinicians that clinical signs, while necessary for a definitive diagnosis, are not perfect and must be evaluated in conjunction with other information. However, if a patient is later found to have Parkinson’s disease, multiple sclerosis, or another disease, their previous FND diagnosis is not necessarily rendered obsolete; rather, the patient is said to have an “overlay” of FND or a comorbidity. Ultimately, if clinicians rely on exaggerated claims about the prevalence of FND and the accuracy and specificity of the required signs, they risk overlooking or ignoring other potential diagnoses or abnormal biologic mechanisms.

Long Covid remains a leading cause of disability. It is therefore essential that physicians, researchers, and policymakers rely on the evidence—and that the evidence does not point to functional neurological impairment as the driving force behind this wave of illness. New studies are documenting daily the long-term impacts of acute coronavirus infection on multiple organ systems in the body, including the central nervous system. Individuals and clinicians are slowly learning how to manage some of the complex and life-altering symptoms, and how not to. To address this urgent medical problem, it is unnecessary and unhelpful to rely on sweeping diagnostic claims based largely—as was the case with conversion disorder—on dubious arguments and unconvincing research claims.

David Tuller, Ph.D., is a senior fellow in public health and journalism at the Center for Global Public Health at the University of California, Berkeley; his academic position is supported by crowdfunded donations to the university, many from people with ME/CFS, long Covid, and related conditions. Mady Hornig, M.D., is a psychiatrist, physician-scientist, and president of CORe Community, Inc. David Putrino, Ph.D., is the Nash Family Director of the Cohen Center for Recovery from Complex…