Diagnosis
A diagnosis of Functional Neurological Disorder (FND) should always be made by a Neurologist, based on positive clinical signs – not by ruling out other conditions.
FND is not a diagnosis of exclusion or a “medically unexplained” condition. It has its own recognisable features on neurological examination and should be diagnosed with confidence and clarity.
However, due to the lack of national NICE guidelines, the complexity of symptoms, and limited access to specialist services, diagnostic approaches can vary across the UK. While some people are diagnosed based on clinical signs alone, others may undergo further tests to help support or clarify the diagnosis.
General Medical Assessment
A full medical history and general examination is performed at the first neurology appointment. This step is vital for understanding the person’s overall health and identifying any other factors that might explain or contribute to their symptoms.
Depending on the situation, the Neurologist may:
Order blood tests (e.g. B12, folate, thyroid function, inflammatory markers).
Review current and past medications to identify potential side effects.
Consider mental health history or life stressors that may affect symptoms.
FND is not an “umbrella” or catch-all diagnosis – it’s essential that a thorough medical assessment is completed as part of the diagnostic process.
Tests and Clinical Signs
FND is identified through positive features seen during the neurological exam – not simply because scans or tests are “normal.”
Some of the clinical signs a Neurologist might use include:
Hoover’s Sign
A test for leg weakness. If a person involuntarily activates the “weak” leg during testing, this shows the motor system is intact – a sign of functional weakness.
Hip Abduction Sign
Identifies inconsistencies in muscle strength that are typical of functional symptoms.
Tremor Entrainment Test
If a tremor changes or stops when the person performs another rhythmic movement, it suggests a functional tremor.
Signs of Functional Seizures
These may include differences in the duration and nature of abnormal movements. When needed, a video-EEG may be used to help distinguish functional seizures from epileptic seizures – though it’s important to note that some individuals may experience both conditions.
These signs are not “normal” findings – they are reliable indicators of FND and form the foundation for diagnosis.
Further Investigations (if clinically needed)
Not everyone needs scans or additional tests. These will be used only when appropriate – for example, if symptoms suggest another condition, or if further clarity is needed in the diagnostic process.
To help you understand what these tests involve, we have included example short explainer videos below.
These investigations are not used to “prove” FND but may help in supporting the diagnosis and ruling out other causes where necessary.
Differential Diagnosis and Avoiding Misdiagnosis
FND symptoms can resemble those of conditions like MS, Parkinson’s disease, epilepsy, and other movement disorders. Additionally, FND may overlap with conditions causing chronic fatigue, weakness, or pain, complicating diagnosis.
FND is not an overall diagnosis – it must be distinguished from other medical or neurological conditions that may coexist. A confident diagnosis of FND should only be made when positive clinical signs specific to FND are clearly observed and explained to the patient. Careful consideration of comorbidities and other potential conditions ensures an accurate diagnosis and helps avoid misdiagnosis.
Common Pitfalls to Avoid in Diagnosing FND
Whilst Functional Neurological Disorder is a positive, rule-in diagnosis, errors can still occur – particularly when clinicians rely on outdated approaches or incomplete assessments.
A 2021 paper by Professor Jon Stone and colleagues, published in the Practical Neurology journal (Stone et al., 2021), outlines several key diagnostic pitfalls to be aware of. These are common reasons for diagnostic error and misunderstanding in FND – both in underdiagnosing and misdiagnosing.
Understanding these helps ensure that people receive a diagnosis that is both accurate and respectfully delivered.
Even if the diagnosis of FND is clear, always ask yourself whether it’s possible this is a patient with FND and another condition, possibly in a prodromal state (for example, functional tremor may occur in the early stages of Parkinson’s disease or functional/dissociative seizures may occur simultaneously with syncope or epilepsy).
There are many odd and unusual symptoms of other neurological conditions (such as geste antagoniste in dystonia, brief frontal lobe seizures with retained awareness and bicycling movements, ability to suppress movements in tics, and ability to self-induce epileptic seizures). The take home message is don’t diagnose FND because a presentation is unusual – there must be clear FND signs.
FND should not be diagnosed just because the patient has psychological comorbidity or recent stress. People with FND do tend to have, on average, more physical and psychological symptoms than equivalent disease controls. They are also more likely to have had adverse experiences both in childhood and more recently (odds ratio ∼2–4). However, all of these clinical features may occur in other disorders (such as multiple sclerosis or epilepsy) which are also associated with higher rates of psychiatric comorbidity. Migraine is a disorder also associated with increased adverse childhood experience in which neuroimaging is also usually normal. Conversely, the diagnosis of FND is often delayed in people without psychiatric comorbidity. FND seems to be especially rare in people with psychosis or where the presenting symptom is psychological.
Many neurological conditions may have normal structural imaging.
Incidental findings are common on brain magnetic resonance imaging (MRI), and disc disease is present in most people after the age of 40 years. Even EEG and cerebrospinal fluid oligoclonal bands can be false positive in some individuals.
To learn more about diagnostic signs and tests specifically for FND, please visit the neurosymptoms website
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