By David Tuller, DrPH
One of my goals next year is to write more about so-called “medically unexplained symptoms,” also known as MUS. The term MUS might be useful as a descriptive name for the large category of phenomena that lack a proven pathophysiological pathway. But in the medical literature, and in the minds of those who present themselves as experts in the field, it is framed as an actual diagnosis that can be delivered with full confidence rather than a provisional construct based on the current state of medical understanding.
Different specialties have their own sub-categories of MUS. In neurology, these are called “functional neurological disorders,” or FND. This term has generally replaced older ones for this concept, including “conversion disorders” and “psychogenic disorders.” As with MUS overall, the evidence for these conditions has resided primarily in the absence of standard signs indicating organic dysfunction. The phrases “conversion disorder” and “psychogenic disorder” mean exactly what they say–the idea is that unexpressed psychological distress is transformed into physical symptoms, although how this “conversion” would occur is not really clear.
In contrast, FND is considered a kinder, gentler phrase. It does not automatically convey the notion of a psychiatric disorder, so the presumption is that the diagnosis is more likely to be acceptable to patients, who can resist being told they do not have an organic illness. The field of neurology has also taken to analogizing FND to “software” rather than “hardware” problems–the latter referring to known neurological disorders with recognized mechanisms. But as with MUS, FND appears to be deployed as a definitive diagnosis rather than as a tentative acknowledgement that doctors simply cannot at this moment pinpoint what the hell is going on and what is generating the troubling symptoms.
A 2018 paper—“You’ve made the diagnosis of functional neurological disorder: now what?”–generated some recent discussion on the Science For ME forum. The authors were affiliated with the neurology and/or psychiatry departments at Harvard Medical School and Brown University, and the paper appeared in Practical Neurology, a BMJ journal. The paper did not raise concerns about the epistemological foundation of the FND category but advised clinicians on how to “enhance diagnostic acceptance and address patients’ doubts.” In other words, patients apparently have a tendency to reject diagnoses that presume their symptoms do not have an organic explanation.
The paper included a statement that triggered my interest; specifically, the authors noted that “there have been significant advances in the diagnostic approach for FND, emphasising a ‘rule-in’ diagnosis based on neurological examination and semiological features.” Hm. What evidence now exists that would allow for a “rule-in” diagnosis of FND, as opposed to diagnosing it solely after ruling out other causes?
One of the cited references was a 2013 paper called “The value of ‘positive’ clinical signs for weakness, sensory and gait disorders in conversion disorder: a systematic and narrative review.” This review, from Swiss researchers, was published by the Journal of Neurology, Neurosurgery and Psychiatry, another BMJ title. Its findings demonstrate the paucity of the evidence behind assertive pronouncements that physical symptoms must have non-organic or psychogenic origins.
Here’s part of the abstract from the review:
“Experts in the field of conversion disorder have suggested for the upcoming DSM-V edition [Diagnostic and Statistical Manual of Mental Disorders, whose fifth edition was published shortly after the review] to put less weight on the associated psychological factors and to emphasise the role of clinical findings. Indeed, a critical step in reaching a diagnosis of conversion disorder is careful bedside neurological examination, aimed at excluding organic signs and identifying ‘positive’ signs suggestive of a functional disorder. These positive signs are well known to all trained neurologists but their validity is still not established.”
The last sentence is telling. I’d rephrase it like this: “Neurologists are all trained to recognize these ‘positive’ signs that can identify people with conversion disorder, and we are certain that these signs can identify people with conversion disorder. Unfortunately, we have no actual evidence that these signs can identify people with conversion disorder.”
The review reports a growing demand for proof of claims that symptoms are not organic beyond the clinician’s failure to identify a pathophysiological cause. Diagnoses in this domain are now expected to be based not just on the lack of evidence for known diseases but also on the presence of clinical findings purportedly characteristic of FND. As the authors write, “This distinction [between organic and functional disorders] is based on the exclusion of neurological signs pointing to a lesion of the central or peripheral nervous system, together with the identification of ‘positive signs’ known to be specific for functional symptoms.”
This emerging evidentiary demand presents neurologists and other clinicians with something of a dilemma, according to the review. As the authors note, “In the era of evidence-based medicine however, clinicians are facing a lack of proof regarding the validity of those clinical ‘positive signs.’”
First, it should be noted that clinicians faced this “lack of proof” long before “the era of evidence-based medicine.” The difference is that in previous years they presumably did not confront the same demands for documentation of these unsupported claims. Under the present circumstances, it is not clear why neurologists and psychiatrists retain such confidence in their pronouncements that some physical symptoms are of non-organic origin. This approach to medicine—making dogmatic declarations and diagnoses despite minimal or no valid evidence–is suggestive of the state of mind known as “emperor-has-no-clothes-ism.”
The review concludes that eleven studies have provided “some degree of validation” for 14 “positive” signs, such as involuntary reflexes, for FND in the categories of “weakness, sensory and gait disorders.” Ten of these eleven studies included 23 or fewer subjects identified with FND. One study included 107 patients identified with FND. In ratings of study quality per the American Academy of Neurology’s classification system, nine of them were designated as Class III—the third out of four grades of quality. Only two included blinding. None included information on inter-rater reliability of these “positive” signs, raising the chances of inconsistencies in how data were interpreted.
According to the authors, overall these “positive” signs have low sensitivity—meaning they would miss many of those who supposedly suffer from FND. The review reports that, in contrast, these signs generally have high specificity—meaning those identified are likely to have the disorder in question. But the review’s account of its own limitations makes clear that even these findings of high specificity cannot be taken at face value.
As the authors write: “As no gold standard exists for functional weakness, sensory and gait disturbances, precise diagnostic criteria on how a diagnosis of functional disorder has been made are not always provided [in the studies reviewed] and wrong attribution of subjects could have occurred. More importantly and more likely, this could have introduced a circular reasoning bias (self-fulfilling prophecy): if the studied sign is also used in the diagnosis process, the reported specificity is overestimated.”
That passage raises a critical point. In studies included in the review, it is possible or even likely that some or many participants were diagnosed at least partly based on “positive” signs that all trained neurologists apparently interpret as suggestive of FND. If that’s the case, then it would not be surprising that assessing the presence of these same signs among these patients would result in high prevalence rates and high specificity. As the authors themselves suggest, this would mean that claims about the diagnostic usefulness of the signs were the result of a self-fulfilling prophecy.
And yet, despite these serious caveats, the study wholeheartedly recommends these signs as helpful tools for diagnosing FND. (The study makes other points as well, of course: about the need for better quality studies to further validate these and other signs for FND, etc.)
From this and related studies, it appears that some neurologists and psychiatrists are engaged in a spirited search for robust data to prove their claims about FND—even as they continue to present these claims as unchallenged knowledge, not as the hypotheses and speculations they actually are. This backward approach to science—seeking evidence for what you have already asserted as fact–strikes me as very Trumpian.