If you have symptoms that might be FND, one of the most confusing parts of the process can be how the diagnosis is actually made. Here's how it works in current practice.

The critical shift: positive signs, not exclusion

The modern approach to FND diagnosis is based on positive rule-in signs — specific, reproducible clinical findings on examination that demonstrate the functional pattern¹. This is a fundamental change from the historical approach of "FND is what's left after we've ruled everything else out."

Current international clinical guidance is explicit: the diagnosis of FND should be based on positive signs demonstrating fluctuation of symptoms with changes in symptom-focussed attention or effort to overcome the symptoms, incongruence with key features of non-functional diseases, or both². FND is a specific, positive diagnosis, not a diagnosis of exclusion³.

Why this matters: patients who receive a clear, positive, well-explained FND diagnosis do better than patients who are told "we can't find anything wrong" or "everything is normal." The diagnosis itself is part of the treatment.

Who can diagnose FND

FND is typically diagnosed by:

Neurologists — the most common diagnostic route, particularly for motor and seizure presentations
Physiatrists (rehabilitation physicians) who work with FND regularly
Psychiatrists with specific training in FND

General practitioners can suspect FND and refer, but the formal diagnosis is usually made at the specialist level given the specificity of the examination findings required.

Increasingly, physiotherapists, occupational therapists, and mental-health providers with FND training are also part of the diagnostic conversation — they may recognize the pattern and refer for specialist confirmation, or contribute to the ongoing diagnostic clarity through their examination findings.

What the exam involves

A defensible FND diagnostic examination looks for specific inconsistencies and incongruities — findings where function varies in different situations. Some examples:

Functional motor symptoms:

Hoover's sign — test hip extension strength on the "weak" leg. When the patient is asked to flex the contralateral hip against resistance, involuntary extension of the "weak" hip is often observed. Strength that is inconsistent with true paresis⁴.
Give-way weakness — sudden loss of resistance during strength testing, unlike smooth weakness in structural conditions.
Movement decreases with distraction, increases with attention — the patient's tremor stops when they're focused on a task with another body part, then resumes when attention returns².
Uneconomic gait — a walking pattern that uses more effort and coordination than a truly weak or ataxic gait would.
Walking, and then being unable to lift a leg off the bed — same voluntary system, but function differs across contexts².

Functional seizures:

Prolonged duration — dissociative attacks commonly last longer than epileptic seizures².
Resisting eyelid opening during the attack, more common in dissociative than epileptic seizures.
Preserved consciousness or partial responsiveness despite convulsive activity.
Asynchronous limb movements during the attack — a pattern rarely seen in epileptic seizures⁵.
Absence of EEG correlates during the attack when captured on video-EEG monitoring.

Functional cognitive disorder:

Symptoms much worse on direct testing than during automatic recall in conversation⁶.
Better delayed recall than immediate recall — the reverse of the pattern typically seen in structural memory disorders.
Attending clinic alone or bringing a written list of symptoms — behaviours inconsistent with the severity of the memory complaints⁶.

Functional dizziness (PPPD):

Symptoms worse in visually complex environments — supermarkets, crowds, patterned floors.
Symptoms respond to specific rehabilitation protocols for PPPD.

What imaging and tests are for

A common patient question is "shouldn't I get more tests?" In FND, additional investigations are ordered:

To rule out specific alternative diagnoses when the clinical picture is genuinely ambiguous
To rule out or characterize comorbid conditions
Not as the basis for the FND diagnosis itself⁷

FND commonly coexists with other neurological conditions — epilepsy plus dissociative seizures, multiple sclerosis plus functional weakness, migraine plus functional visual symptoms are all documented combinations⁸. Having FND does not mean you don't also have something else; the two can be simultaneously true.

Misdiagnosis rates

FND misdiagnosis rates are lower than many patients (and some clinicians) assume. A study following patients diagnosed with FND in neurology clinics for 18 months found only a 0.4% misdiagnosis rate⁸. This is much lower than the misdiagnosis rate for many other neurological disorders. In other words: when FND is diagnosed by a competent clinician using positive signs, the diagnosis is reliable.

How the diagnosis is communicated

Good FND diagnosis communication includes:

Naming the condition clearly — "You have functional neurological disorder"
Explaining how the diagnosis was made — showing the patient the specific rule-in signs
Framing the biology — that FND is a real disorder of nervous system function, not "made up" and not a moral failing
Explaining that recovery is possible — this is a treatable condition with real evidence-based treatments
Providing educational materials and setting up the treatment team

The FND Society and organizations like FND Hope provide patient-facing educational materials that many neurologists share at diagnosis.

When to seek a second opinion

Sometimes a second opinion is genuinely useful:

The diagnosis was made purely as "everything else is normal, so it must be functional" without positive signs
The clinician was dismissive or used older stigmatizing language ("psychogenic," "hysterical")
Symptoms are worsening in ways that don't fit the FND picture
New neurological symptoms emerge that could suggest a coexisting condition
No coordinated treatment plan has been offered

A knowledgeable FND clinician can generally re-examine, review previous investigations, and either confirm the diagnosis with clear rule-in signs or reassess.

Next steps

For an overview of what FND is: FND: A Neuroscience-Informed Introduction. For the "is this real" question: Is FND Real? Understanding the Neurobiology. For treatment: How Is FND Treated?.

If you'd like to talk about the mental-health-side of FND care, book a free 15-minute consultation.

References

¹: Positive Clinical Signs in Functional Neurological Disorders: A Narrative Review. PMC 12468354.

²: Managing Functional Neurological Disorders — Australian treatment recommendations, 2024.

³: Brigham and Women's Hospital. Functional Neurologic Disorder Standard of Care. "FND should never be described as a diagnosis of exclusion, but rather one that is comprised of specific clinical features."

⁴: Positive Clinical Signs, ibid.

⁵: Managing FND, ibid.

⁶: Positive Clinical Signs, ibid.

⁷: Managing FND, ibid.

⁸: BMJ Neurology Open (2025). Managing Functional Neurological Disorders. Cites 0.4% misdiagnosis rate over 18 months.

How Is FND Diagnosed? Positive Signs, Not Exclusion