A normal scan is not a normal brain: the diagnostic gap in functional neurological disorder

A clinician who manages one of the few multidisciplinary clinics for functional neurological disorder has described, in The Conversation, a pattern that has not changed much in decades: patients arrive having been told their brain scan was normal, their electroencephalogram was reassuring, and the good news is that they do not have epilepsy ^[6][3]. That sequence ends in an exclusion, not a diagnosis, and the consequence is that people who cannot walk without falling, whose leg will not stop trembling, or who have seizures that leave them exhausted for hours or days leave the appointment with nothing ^[4][1].

The framing matters because the condition is not rare. The article characterises functional neurological disorder as one of the most common brain disorders and one of the most misunderstood ^[1]. The author reports seeing the same arc repeatedly: long diagnostic journeys, sustained uncertainty, then the relief of finally being believed ^[7]. Some patients, before that point, begin to wonder whether they are imagining the symptoms ^[5]. Laura Strom, one of the neurologists at the clinic, tells patients: "Well, it's good that it's all in your head - because that's where your brain is" ^[8].

The mechanistic account on offer is not an appeal to sympathy. Brain imaging studies suggest that the networks handling movement, attention, emotion, body awareness and sensory processing are in constant communication and act together rather than independently, and how they communicate and occasionally miscommunicate is one of the central open research questions in the condition ^[10][11]. The leading explanatory framework described is predictive processing: the brain continuously generates predictions by combining past experience, information from the surroundings and signals from inside the body ^[12]. Walking up stairs does not involve consciously calculating foot placement, because the movement has already been predicted, and most of the time those predictions are accurate ^[21]. When incoming information does not match the prediction, the mismatch is called prediction error, and researchers believe disruption of the updating process that resolves it may be one mechanism behind the disorder ^[13].

There is no single cause, but injury, illness, pain or significant stress may push the brain toward relying on prior predictions instead of new information, and weighting priors or particular bodily signals too heavily makes updating harder ^[14][15]. The worked example is concrete: after an injury has healed, the brain may keep predicting that a movement is unsafe, which can contribute to persistent weakness or difficulty walking ^[16]. The symptoms are involuntary, physically real and profoundly disabling even though no damage is occurring to the brain or nervous system ^[17].

That is why the older labels are doing active harm. The condition has been called hysteria and conversion disorder, and conceptualised as psychogenic, meaning symptoms were assumed to arise primarily from psychological factors rather than biological changes in the brain ^[18]. Each name reflected the best explanation medicine had at the time, and none of them described what patients were actually experiencing ^[19]. Treating the disorder as a disconnect between brain and body is a sharp departure from a century of that thinking ^[20].

Worth watching: whether the network-communication research firms up into tests that rule the condition in rather than out, and whether multidisciplinary clinics of the kind described remain few ^[11][6].