Functional neurological disorder: my minimum evidence standard

Step 01

FND is listed in ICD-11 with mental health conditions, but the impairments it causes are often physical and neurological

ICD-11 classification

ICD-11, the World Health Organization's classification of diseases, files FND under dissociative disorders, in its chapter on mental, behavioural and neurodevelopmental disorders. The symptoms, though, are physical: weakness, abnormal movement, seizures, and loss of speech or sensation.

That placement doesn't decide what kind of impairment FND causes. In the one FND decision in my index, the Tribunal accepted both a physical and a neurological impairment arising from FND (ZTDG [139]). A strong file names the impairments themselves (for example, weakness in the right leg, gait disturbance, functional seizures) rather than leaving the NDIS to infer them from a mental health code. It also records the subtype, because each person's FND looks different, and many people have more than one.

The next step is what's driving the symptoms.

Step 02

FND is a problem with how the brain controls movement and sensation, not damage to it, and any pain has its own mechanism

Mechanism

Current models describe FND as a disorder of how the brain controls and perceives movement, sensation and awareness: changes in attention to the body, in expectations about movement, and in the sense of voluntary control. There is no structural damage to find. That's why normal scans and tests are expected in FND, and why they don't count against the diagnosis.

Pain often comes with FND but isn't part of it. Pain is classified by mechanism: nociceptive (from tissue), neuropathic (from nerve injury or disease), or nociplastic (from altered pain processing in the nervous system). In FND, where pain is present, it is nociplastic. A strong file says so, so each treatment can be matched to what it was aimed at, and the NDIS doesn't have to guess.

The next step is the criteria the diagnosis is checked against.

Step 03

FND is diagnosed against the DSM-5-TR criteria

Diagnostic criteria

AAPT has not published criteria for FND, because it isn't a pain condition. The recognised standard is DSM-5-TR (functional neurological symptom disorder). Under it, FND is diagnosed on positive signs found on examination, not by ruling everything else out.

A file that calls FND a “diagnosis of exclusion” is weaker for it. Current practice is that “positive signs are essential in supporting a phenotype-based diagnosis that does not depend on excluding other disorders” (Espay et al 2018). In the FND decision in my index, the GP described FND as a “diagnosis of exclusion” [138], and the Tribunal found permanence premature while neurology review continued [179]–[180].

For functional seizures, the International League Against Epilepsy sets out levels of certainty, from possible (a witness account) to documented (a typical event recorded on video-EEG, with no epileptic activity). A strong file says which level was reached (LaFrance et al 2013).

Once the diagnosis is settled, the question most refusals come down to is what has been tried.

Step 04

An FND treatment history is easiest to read when it covers the same nine elements I check on every file

Treatment history · s 24(1)⁠(b)

Whether the NDIS accepts an impairment as permanent usually comes down to the treatment record. I check it against the nine elements I use for pain management (HEAPPPPSS). FND treatment is usually led by rehabilitation: specialist physiotherapy for movement symptoms, psychological therapy (especially for functional seizures), occupational therapy, and speech pathology where speech or swallowing is affected. For each element, the table names a published source that covers it for FND. For a support request, the same record shows where treatment ends and disability support begins, which is how the NDIS decides whether the health system should fund it instead.

For each element in your file, the NDIS looks for what was done and what happened, by whom (and whether they work with FND), and what changed, in function as well as symptoms. If an element never appears, the file says nothing about it, and the NDIS decides what that silence means.

That includes mental health care. In the FND decision in my index, separate mental health impairments failed on permanence because a recommended psychiatric review and psychological therapy hadn't happened [160]–[163], and the GP had believed therapy was under way when it wasn't [158].

Permanence is one requirement. Function is the other one an FND file most often has to show.

FND function is shown best across a whole day and the week that follows, not in one appointment

Function over time · s 24(1)⁠(c)

FND symptoms vary from hour to hour and day to day, and are often worse with fatigue, pain or illness. Fatigue is often a major limit in its own right. A single appointment sees one moment, so it tends to make you look more capable than you are. Where seizures are part of the picture, a count does more than a description: how many, how long, and how long recovery took, over a stated period. In the decision above, the Tribunal had no reliable count [177] and found no impairment from the seizures [141].

A strong file follows what happens after a run of ordinary activities. I follow up at 24 hours, 72 hours and 7 days.

For an access request, I then match what your file shows to the six activity domains in s 24(1)⁠(c), the areas of daily life the NDIS assesses. For a support request, the same record shows what the support keeps you doing and what slips without it. Either way, that's done for each person, not for each condition.

The one published FND decision in the index shows how a file like this fared at the Tribunal.