Trial By Error: No Evidence for CBT and Other “Conversion Disorder” Therapies

By David Tuller, DrPH

I have recently written critically about the CODES trial of cognitive behavior therapy as a treatment for the phenomena that have long been called “psychogenic non-epileptic seizures” but that some neurologists and psychologists are trying to rebrand as “dissociative seizures.” (Many people understandably find it offensive to be told they have a “psychogenic” disorder; perhaps the term “dissociative” comes across as less dismissive.) Now Cochrane has published a review that relates directly to this issue–“Psychosocial interventions for conversion and dissociative disorders in adults.”

The new review is an update of a 2005 version. Its stated objective was “to assess the beneficial and harmful effects” of the psychosocial interventions in question, several of which were forms of CBT. The review included 17 studies published up until last year, with a total of 894 participants. The 2010 pilot study for CODES was included, although CODES itself was published too late. The Cochrane review found that the studies were generally of poor quality and produced little or no evidence of benefits from a range of psychosocial interventions.

Here are the conclusions of the Cochrane review:

The results of the meta-analysis and reporting of single studies suggest that there is lack of evidence regarding the effects of any psychosocial intervention of conversion and dissociative disorders in adults. It is not possible to draw any conclusions about potential benefits or harms from the included studies.

The study’s main authors were mental health experts at Danish psychiatric and psychological centers. It is therefore not suprising that the language used in the review suggests they take the purportedly psychogenic nature of these conditions at face value. Here’s the abstract’s “background” section:

Conversion and dissociative disorders are conditions where people experience unusual neurological symptoms or changes in awareness or identity. However, symptoms and clinical signs cannot be explained by a neurological disease or other medical condition. Instead, a psychological stressor or trauma is often present. The symptoms are real and can cause significant distress or problems with functioning in everyday life for the people experiencing them.”

Noting that the reported symptoms “cannot be explained by a neurological disease or other medical condition” implies that such an explanation does not exist. The other possible explanations, that the underlying pathophysiological causes have been missed or that the science has not yet identified them, do not appear to have been considered. But that’s a shortcoming of the studies included in the review as well, given that they were mostly based on hypothesized and unprovable mechanisms like the “conversion” of psychological distress into somatic complaints.

It does seem like some psychiatrists and neurologists have sought to supplant the conversion and psychogenesis framings, as the use of the term “dissociative” suggests. In CODES, the investigators do not present the medical events they are studying as psychogenic or examples of conversion disorder. But if understanding of the phenomenon of unexplained seizures has evolved beyond the reductive constructs of conversion and psychogenesis, it is unclear why a form of CBT based on those constructs would still be appropriate. The CODES paper does not explain why the investigators decided to test an intervention grounded in a strictly psychogenic model that they seem to believe is outdated.

Had the null results in CODES for the primary outcome of seizure frequency at 12 months been included in the Cochrane analysis, they would certainly have reinforced the review’s conclusions. In CODES, participants who did not receive CBT designed to reduce seizures experienced greater seizure reduction at 12 months than those who did receive the specialized intervention, although the results were not statistically significant.

For the CODES investigators, the results from the pilot were convincing enough to proceed with a huge trial. Yet in assessing the 2010 pilot study, the Cochrane review described the findings like this: “Cognitive behavioural therapy may have little or no effect on reducing physical signs [monthly seizure frequency] at end of treatment.” Cochrane rated the certainty of the evidence produced by the pilot study as “low” per the GRADE system, which defines “low” this way: “further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.”

We have since had that further research, CODES–and can say with a certain amount of confidence that CBT does not reduce seizure frequency at 12 months. (I have previously addressed why the secondary outcomes are basically meaningless, even though they were the basis on which King’s College London hailed CODES as a great success.)

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