Neurological symptoms — weakness, tremor, seizures — without a structural lesion in the nervous system. Real, treatable, and better understood every year.
Imagine a computer whose hardware is completely fine — but the software has a bug. The computer behaves strangely: freezes, has errors, doesn't respond. This is how functional neurological disorder works. The hardware — the brain, spinal cord, nerves — is structurally intact. But the way the nervous system processes and generates signals has gone wrong. That is why symptoms are real and visible, even though a brain scan appears normal.
Functional neurological disorder (FND) — previously called conversion disorder — is a condition in which a person develops neurological symptoms (weakness, tremor, non-epileptic seizures, gait disturbance, sensory disturbances) that cannot be explained by structural damage or disease of the nervous system.
The word "functional" is key: the problem lies in how the nervous system functions — in how it processes, generates, and controls signals — not in its structure. This is why scans are normal. And this is not a deficiency of the diagnostic method; it is accurate information about the nature of the problem.
FND is not a rare condition. Studies estimate it affects approximately 2–5% of all outpatient neurology visits. In children and adolescents, it is one of the most common reasons for referral to paediatric neurology — and also one of the most misunderstood.
Symptoms are divided into several categories. They can occur individually or in combination.
FND represents perhaps the clearest example of the inseparability of body and mind. Neuroimaging studies in patients with FND show genuine differences in brain activity — in the areas responsible for attention, motor control, and emotion processing. These are not imagined differences: they are measurable biological changes.
Current models understand FND as a disorder of predictive processing — the brain's ability to create predictions about bodily sensations and movements. In FND, this prediction process becomes disrupted: the brain produces abnormal motor or sensory predictions that result in real symptoms.
An important observation: symptoms in FND very often respond to suggestion, distraction, or emotional triggers. This is not proof of "fabrication" — it is evidence of how closely mental and physical functions are interwoven.
One of the most important advances in the understanding of FND is the shift from diagnosis by exclusion to positive diagnosis. This means the diagnosis is not made simply because "all tests are normal" — but because specific clinical signs are present that are characteristic of FND.
Examples of positive clinical signs:
Positive diagnosis changes everything: the child and family receive a clear explanation — not a message of uncertainty — and treatment can begin immediately.
The goal of treatment is not to "prove it isn't neurological" — that question has already been answered. The goal is to help the nervous system relearn. And that is possible.
Zala was 13 when, after a minor sports injury, weakness of her left leg appeared — and didn't go away after the injury healed. Within a few months she was in a wheelchair.
Zala is 16 and has been walking independently for more than a year. She still attends psychological support sessions and says: "FND taught me that I need to listen to myself. To know my limits. That's a lesson I wouldn't trade."
The name has been changed. The story was published with the family's permission.
