Functional neurological disorder carries a lot of historical baggage. It is the updated name for the hoary Freudian diagnosis of
conversion disorder, in which people are said to be “converting” psychological trauma into physical ailments like arm or leg paralysis. (Once upon a time not so long ago, some people with these conditions — especially women — would have been diagnosed with
hysteria.) In the last two decades, clinicians have tried to rebrand conversion disorder, recognizing that their patients often disliked being told their symptoms were psychosomatic.
In 2013, psychiatry’s Diagnostic and Statistical Manual of Mental Disorders
officially adoptedthe more neutral-sounding term “functional neurological symptom disorder” as an alternate name for conversion disorder. (In practice, the word “symptom” is usually dropped.) This update was accompanied by new diagnostic criteria. Beside the lack of a better explanation for the symptoms, a diagnosis of FND now also required the presence of positive clinical signs said to be incompatible with recognized neurological and other medical conditions, such as physical reflexes in an apparently paralyzed limb.
These days, neurologists and other experts frequently describe FND as a “brain network” disorder, with symptoms purportedly rooted in disruptions to
“the predictive machinery of the brain,” faulty perceptions of self-agency, and hypersensitivity to bodily sensations, among other factors. FND
is also described as a problem exclusively with the brain’s “software” (how the brain functions) rather than with its “hardware” (or structural elements). Where biological changes at the cellular, intracellular, or extracellular levels — such as possible alterations to mitochondria or to epigenetic profiles — fit within this schema, or if they do at all, remains extremely murky.
