FND Dictionary and Abbreviations

FND is complex and it has a lot of complex terms. It confused the medical world and their patients.

We hope this page can help explain some of the terms that are used.

Please note that the terms have changed over time, and different terms do not necessarily mean different conditions.

Term	Plain-English meaning
Central nervous system (CNS)	The brain and spinal cord. These coordinate movement, sensation, thought and many automatic bodily functions.
Chronic fatigue	Severe or persistent tiredness that is not fully relieved by rest. Fatigue commonly accompanies FND but can also have many other causes.
Cognitive symptoms	Difficulties involving attention, memory, concentration, thinking or finding words.
Comorbidity	Another condition occurring alongside FND, such as migraine, chronic pain, anxiety, depression, fibromyalgia or IBS.
Conversion disorder	An older name for FND that is still used in the American DSM diagnostic system. It arose from the theory that psychological distress was “converted” into physical symptoms. This explanation does not fit everyone with FND.
Derealisation	A feeling that the surroundings are unreal, distant, dreamlike or strangely unfamiliar. It is one form of dissociation.
Depersonalisation	Feeling detached from yourself, your thoughts or your body—for example, as though you are observing yourself from outside.
Dissociation	A temporary disruption in awareness, memory, identity, sensation or connection with the body or surroundings. Some people experience dissociation before or during functional seizures, but not everyone with FND experiences it.
Dissociative neurological symptom disorder	The name used for FND-related symptoms within the World Health Organization’s ICD-11 classification system.
Dissociative seizures	Episodes that can resemble epileptic seizures or blackouts but are not caused by epileptic electrical activity. Also called functional seizures, PNES or NEAD.
Distractibility	A clinical sign in which a symptom changes or reduces when the person’s attention is directed elsewhere. This is not deliberate and can help support an FND diagnosis.
Drop attack	A sudden fall, sometimes without losing consciousness. Drop attacks have several possible causes; in some people they are a functional neurological symptom.
DSM-5-TR	The current version of the American Psychiatric Association’s diagnostic manual. It uses the name functional neurological symptom disorder (conversion disorder).
Entrainment	A diagnostic sign, particularly in functional tremor. The tremor may change rhythm when the person copies a different rhythm with another part of the body.
Epilepsy	A neurological condition involving seizures caused by abnormal electrical activity in the brain. Epilepsy and functional seizures are different, although a person can have both.
Etiology / aetiology	The cause or causes of a condition. FND rarely has one simple cause and may involve several biological, psychological and social factors.
Flare-up	A temporary increase in symptoms. This does not necessarily mean that the condition is permanently worsening.
FMD – Functional movement disorder	FND symptoms that mainly affect movement, such as tremor, jerks, spasms, dystonia or difficulty walking.
FND – Functional neurological disorder	A condition in which the nervous system is not functioning properly, causing genuine neurological symptoms. The problem concerns how brain networks are working rather than damage that would necessarily appear on a conventional scan.
FNSD – Functional neurological symptom disorder	Another name for FND, commonly encountered in diagnostic manuals, research papers and medical records.
Functional	In FND, “functional” means that the problem concerns how the nervous system is working or communicating. It does not mean that symptoms are imaginary or deliberately produced.
Functional cognitive disorder (FCD)	Persistent problems with memory, attention or thinking that are related to how cognitive processes are functioning rather than a degenerative brain disease such as dementia.
Functional dizziness	Persistent or recurring dizziness related to altered processing of balance, movement and visual information. PPPD is a common form.
Functional dystonia	Abnormal and often painful posturing, twisting or fixed positioning of a body part occurring as part of FND.
Functional gait disorder	Difficulty walking caused by FND. This can include dragging a leg, unsteadiness, sudden knee buckling or an unusual walking pattern.
Functional jerks / functional myoclonus	Sudden, brief, shock-like movements occurring as part of FND. “Myoclonus” simply describes the type of movement and can also occur in other conditions.
Functional limb weakness	Genuine weakness or difficulty controlling an arm or leg caused by altered nervous-system functioning rather than structural damage to the relevant movement pathways.
Functional overlay	A sometimes controversial term suggesting that functional symptoms exist alongside another medical or neurological condition. It should not be used to imply that someone is exaggerating their underlying illness.
Functional seizures	The increasingly preferred name for seizure-like or blackout episodes caused by FND rather than epileptic electrical activity. Also known as dissociative seizures, PNES or NEAD.
Functional sensory symptoms	Altered sensation caused by FND, including numbness, tingling, burning, unusual sensitivity or a feeling that part of the body does not belong.
Functional speech or voice symptoms	Changes such as stuttering, slurred speech, whispering, loss of voice, altered accent or difficulty producing words as part of FND.
Functional tic-like behaviours (FTLB)	Sudden movements or sounds that resemble tics but develop through functional neurological mechanisms. They can coexist with Tourette syndrome or other tic disorders.
Functional tremor	Shaking caused by FND. It may vary in speed or intensity and can sometimes change with distraction or when performing a rhythm with another limb.
Globus sensation	A feeling of a lump, tightness or something stuck in the throat when no physical blockage is present. It can occur as a functional symptom but should be medically assessed when appropriate.
Grounding	Techniques used to reconnect attention with the present moment and the body. Examples include noticing the environment, feeling the feet against the floor or slowing the breath.
Hoover’s sign	A physical examination sign used to identify functional leg weakness. It shows that automatic leg movement may remain stronger than movement produced when consciously trying.
Hypervigilance	The nervous system being unusually alert to possible threats, bodily sensations or signs that symptoms may begin.
Hysteria	An obsolete historical label once used for many symptoms now understood as FND. It is considered inaccurate and stigmatising and should no longer be used diagnostically.
ICD-10 / ICD-11	International systems published by the World Health Organization for classifying illnesses and health conditions. Terminology for FND differs between versions and countries.
Inconsistency	A diagnostic feature in which a person’s ability changes between tasks or situations in ways that follow recognised FND patterns. It does not mean the person is being dishonest.
Involuntary	Something that happens without conscious choice or deliberate control. FND symptoms are involuntary.
MDT – Multidisciplinary team	Professionals from different specialities working together. An FND MDT might include neurology, physiotherapy, occupational therapy, psychology, psychiatry and speech and language therapy.
Motor symptoms	Symptoms affecting movement, such as weakness, tremor, spasms, jerks, abnormal posture or walking difficulties.
NEAD – Non-epileptic attack disorder	A UK term for functional seizure-like episodes that are not caused by epilepsy. “Functional seizures” or “dissociative seizures” are now often preferred.
NES – Non-epileptic seizures	A general term for seizure-like episodes not caused by epilepsy. It is often used to mean functional seizures, although technically non-epileptic episodes can have other medical causes.
Neuroplasticity	The nervous system’s ability to change and learn. Rehabilitation for FND aims to use this ability to develop more helpful patterns of movement, attention and symptom regulation.
Neuropsychiatry	A medical speciality concerned with conditions involving both neurology and mental health. Some FND services are based within neuropsychiatry.
Neurological	Relating to the brain, spinal cord, nerves or the way these parts of the nervous system communicate.
Neurologist	A doctor specialising in conditions affecting the brain, spinal cord, nerves and muscles. Neurologists often diagnose FND using history, examination and positive clinical signs.
Neurophysiotherapy	Physiotherapy specialising in neurological symptoms. In FND it often focuses on restoring automatic, confident movement rather than concentrating intensely on each movement.
Occupational therapy (OT)	Support to help someone manage everyday activities, work, fatigue, routines, sensory difficulties and independence.
Pacing	Balancing activity and rest to reduce cycles of doing too much on better days and then experiencing a significant symptom flare or “crash.”
Paralysis	Complete or near-complete loss of voluntary movement. Functional paralysis can occur even though the basic movement pathways remain physically capable of working.
PNES – Psychogenic non-epileptic seizures	A widely used term for functional seizures. Some people and clinicians avoid it because “psychogenic” can incorrectly imply that every episode has a purely psychological cause.
Positive diagnostic signs	Examination findings that actively support an FND diagnosis, such as Hoover’s sign, tremor entrainment or improvement with distraction. FND should not be diagnosed simply because tests are normal.
PPPD – Persistent postural-perceptual dizziness	Persistent dizziness or unsteadiness that is often worse when upright, moving or surrounded by busy visual patterns. It commonly overlaps with FND.
Precipitating factor	Something occurring around the time symptoms begin, such as illness, injury, pain, migraine, panic, a medical procedure or severe stress. Sometimes no clear precipitating factor is found.
Predisposing factor	Something that may make a person more vulnerable to developing FND. It is not necessarily the direct cause, and some people have no identifiable predisposing factors.
Prognosis	The expected course of a condition, including the likelihood of improvement, persistence or relapse. FND prognosis varies considerably between individuals.
Proprioception	The brain’s sense of where the body and limbs are positioned without needing to look at them. Altered processing of this information may contribute to some FND symptoms.
Pseudoseizure	An outdated and potentially offensive term for functional seizures. “Pseudo” can wrongly suggest that the episode is fake. Functional seizures are genuine and involuntary.
Psychogenic	Meaning thought to originate from psychological processes. The term appears in PNES and older FND literature but may oversimplify the multiple mechanisms involved.
Psychosomatic	Describes interaction between psychological processes and physical symptoms. It does not mean that symptoms are imaginary, although the word is sometimes misunderstood or used dismissively.
Relapse	The return or worsening of symptoms after a period of improvement. Relapses can occur during recovery and do not mean that all previous progress has been lost.
Retraining	Practising different patterns of movement, attention or response so that the nervous system gradually learns a more helpful and automatic pattern.
Seizure	A sudden episode involving altered movement, sensation, awareness or behaviour. Seizures have several possible causes and are not always epileptic.
Sensory symptoms	Changes in physical sensation, such as numbness, tingling, pain, burning, altered temperature or unusual sensitivity.
Somatic symptom disorder (SSD)	A separate diagnosis involving excessive distress, thoughts or behaviour concerning physical symptoms. It is not another name for FND, although the two can occasionally coexist.
Speech and language therapy (SLT)	Treatment for difficulties involving speech, voice, communication or swallowing. Specialist SLT can help with functional speech, voice and swallowing symptoms.
Structural disorder	A condition involving identifiable damage or disease in body tissues, such as a stroke or multiple sclerosis lesion. FND concerns nervous-system functioning, although functional and structural conditions can coexist.
Syncope	Fainting caused by a temporary reduction in blood flow to the brain. It is different from epilepsy and functional seizures, although the episodes can sometimes look similar.
Trigger	Something associated with symptoms starting or worsening. Triggers can include movement, pain, fatigue, illness, sensory overload, strong emotions or particular environments. A trigger is not necessarily the original cause.
Variability	Symptoms changing over time, between activities or according to attention and circumstances. Recognised patterns of variability can provide positive evidence for FND.
Video EEG / video telemetry	A test that records video and the brain’s electrical activity together. Capturing an episode can help distinguish functional seizures from epileptic seizures.

Important: This dictionary is intended to explain terminology, not diagnose symptoms. Similar symptoms can have several different causes, and FND can occur alongside another neurological or medical condition. New or changing symptoms should be assessed by an appropriately qualified healthcare professional.