FND Education Project

REFERENCE · DIAGNOSIS

Functional Jerks or Myoclonus

Refers to:

  • sudden, brief, non-rhythmic limb, trunk or whole-body jerks;
  • isolated jerks or repeated clusters; and
  • assessed functional myoclonus or startle-like jerks.

Scope boundary: Rhythmic oscillation belongs on the tremor page, patterned posturing on the dystonia page, and a larger episodic event on the functional-seizures page. The laboratory method below applies to repeated jerks that can be recorded, not every sudden movement.

Quick Reference

Functional jerks are involuntary sudden movements assessed through their clinical pattern and, when needed, specialist recordings.

Motor and vocal tic-like symptoms

Jerks and tic-like symptoms may look similar but are not interchangeable diagnoses. Motor tics can coexist with jerks. See the dedicated functional-tics page.

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Myoclonus is the clinical term for sudden, brief jerk-like movements. Functional jerks may vary in timing, distribution and response to attention, but some non-functional forms of myoclonus can also be irregular. Complex cases may need specialist neurophysiology rather than visual judgement alone. [1][2]

Neurophysiology: Tests of how nerves, muscles and the brain work, often using electrical recordings.

A jerk might interrupt a sip of water or a movement you were trying to make. What matters at the appointment includes both the movement and what it interrupts. Tell the clinician which activities become difficult, what help makes them possible, and what happens afterwards. These are conversation prompts, not a list of effects everyone must have.

What the recordings are looking for

Surface EMG records when particular muscles activate. EEG records electrical activity from the scalp. When many jerks are recorded, a computer can align the EEG to the beginning of each muscle burst and average what happened beforehand. A slowly developing premovement signal called a Bereitschaftspotential may support a functional origin in the right clinical setting. Its absence does not rule functional jerks out. [1]

This signal does not mean the person consciously planned the movement. It is a laboratory observation about movement preparation and must be explained without equating brain preparation with voluntary control.

The recording can help distinguish movement patterns. It does not read your thoughts or tell the team how much assistance you need. If there are too few usable jerks, the result may remain uncertain. The team should explain whether a signal was absent in an adequate recording or the recording could not answer the question. [1][11]

A brief jerk can be part of a long episode

An individual jerk is brief, but that does not mean the problem has to be brief. Jerks may occur occasionally, come in repeated clusters or bouts, recur throughout a longer flare, or be part of a more persistent movement pattern. A clinician needs to understand that time course alongside the examination. A trigger or an irregular rhythm alone does not establish the cause. [1][2]

At the start of a familiar bout, move away from fall, heat, sharp-object or driving hazards and sit or obtain support if needed. Use the agreed recovery and bout-management plan. A new pattern, repeated injury, altered awareness or another major change deserves reassessment. Seek urgent help for serious injury, breathing difficulty or prolonged unresponsiveness.

Other explanations and what remains uncertain

Some jerks arise from abnormal activity in the brain’s outer layer, from other nervous-system pathways, from medicines or from disturbances in body chemistry. Tics and exaggerated startle responses can resemble jerks too. The history, examination and selected investigations help distinguish these possibilities; a normal routine EEG alone does not establish FND. [2][11]

Research explores differences in movement preparation and attention in functional jerks. These are possible contributing processes, not a complete account of why a particular person’s symptoms started. A diagnostic finding may help explain the pattern while leaving questions about cause open. [7]

Everyday function and wellbeing

A quiet period during the appointment cannot describe the whole day. Discuss the reliability of eating, dressing, moving around or using equipment, including the support you use and the time you need afterwards. Assessment and everyday function explains why diagnosis and daily ability need separate attention.

One small study found similarly affected quality of life and similar depression and anxiety scores in people with functional jerks and people with cortical myoclonus. Emotional wellbeing deserves care whichever diagnosis applies; those scores did not distinguish the diagnoses. [10]

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Ask what the person would like you to explain before the appointment. With permission, describe an ordinary example: what they were doing, whether the jerks came singly or in clusters, how awareness was affected, and what help or recovery time was needed.

Do not startle, tap or expose the person to loud sounds to try to bring out a jerk. Even when stimulus sensitivity is assessed clinically, it requires a planned specialist protocol and attention to distress, falls and injury. A home video may help only if a spontaneous event can be recorded safely without delaying care.

During recording or examination

Help communicate sensory sensitivities, pain, communication needs or difficulty maintaining a position. Agree a way to ask for a break. If no representative jerk occurs, that is useful information about the limits of the session; there is no need to make symptoms happen for the assessment.

When a bout begins

The jerks themselves may each last only a moment while the bout continues much longer. Help remove hazards and offer the person’s usual seat or support. Follow their existing bout plan. Avoid holding a limb down or adding repeated instructions.

If wanted, help record the clinician’s explanation: what finding supported the diagnosis, what the test could not answer, and who will follow up. Ask how ongoing assistance and daily activities will be assessed separately from the laboratory result.

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Episodic and prolonged presentations

Distinguish the duration of each jerk from the duration of the clinical episode. Document whether jerks are isolated, clustered, quasi-continuous or embedded in a broader flare; record frequency, warning, task and environmental context, relation to other motor or seizure-like symptoms, awareness, injury and recovery. Functional motor symptoms can be recurrent or persistent. Episodicity or stimulus sensitivity alone is not diagnostic. [1][2]

Describe spontaneous and action-related movements, body distribution and associated neurological findings. Consider cortical, subcortical, spinal and peripheral generators, medication/toxic-metabolic causes, tics and startle syndromes. Select investigations for the suspected cause. Functional symptoms and other disease can coexist. [2][11]

Cortical: Arising from the brain’s outer layer. Subcortical: Arising from structures below that layer. Toxic-metabolic: Related to a substance or disturbance in the body’s chemistry.

Selecting specialist investigations

The EEG–EMG assessment links muscle timing to brain activity. Burst duration and recruitment contribute to interpretation; they are not isolated diagnostic cutoffs. A brief jerk-linked cortical spike and a slow readiness potential answer different questions. Findings for recorded jerks do not classify every accompanying episode. [1][2]

When jerks are too intermittent to observe in clinic, safely obtained video may help phenotype the event. Neurophysiological testing requires enough representative jerks for analysis and should not be pursued by provoking a hazardous or highly distressing bout solely to obtain data.

Diagnostic techniques at a glance

All nine original entries remain in the full inventory. One detailed page now explains the featured combined assessment. Other entries remain brief summaries or contextual adjuncts, not completed standalone protocols.

The detailed recording and analysis page replaces the former brief outline.

The media brief has moved with the procedure.

Function, quality of life and care-team roles

Neurology and neurophysiology should explain the pattern, diagnostic confidence and outstanding questions. OT and physiotherapy can assess task safety, adaptations, repeated performance and assistance. Mental-health care should respond to the person’s concerns and needs. A readiness potential is not a measure of disability, motivation or treatment response. [1][12]

Zutt and colleagues compared 16 people with functional jerks and 23 with cortical myoclonus at a tertiary centre. Self-rated mood scores did not separate the groups, and quality of life was similarly impaired, with more pain reported in the functional group. Small samples, referral selection and questionnaire exclusions limit generalization. This association cannot establish the cause of an individual’s jerks. [10]

Ask about injury risk, reliable task completion, support, fatigue and recovery cost where relevant. These are questions for assessment, not consequences inferred from a waveform. Rehabilitation and flare management remain in the paired recovery collection.

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Research and Sources

Evidence notes

The IFCN chapter and 2025 study-group review place recordings within clinical assessment. Primary evidence and access limits are described on the detailed technique page. Original citations 1–8 retain their identifiers for the inventory; this is not a claim that every inventory paper has undergone fresh full-text review. Tic-like symptoms retain their separate clinical framework. [1][9][11]

Citation table

Citation Figure Full citation
[1] — Edwards MJ, Koens LH, Liepert J, Nonnekes J, Schwingenschuh P, van de Stouwe AMM, Morgante F. Clinical neurophysiology of functional motor disorders: IFCN Handbook Chapter. Clinical Neurophysiology Practice. 2024;9:69–77. FND-CIT-0022. https://doi.org/10.1016/j.cnp.2023.12.006
[2] — van der Veen S, Caviness JN, Dreissen YEM, et al. Myoclonus and other jerky movement disorders. Clinical neurophysiology practice. 2022;7:285-316. DOI. PMID: 36324989. FND-CIT-0151.
[3] — Zutt R, Elting JW, van der Hoeven JH, et al. Myoclonus subtypes in tertiary referral center. Cortical myoclonus and functional jerks are common. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 2017;128(1):253-259. DOI. PMID: 27940047. FND-CIT-0186.
[4] — van der Salm SM, Koelman JH, Henneke S, et al. Axial jerks: a clinical spectrum ranging from propriospinal to psychogenic myoclonus. Journal of neurology. 2010;257(8):1349-1355. DOI. PMID: 20352254. FND-CIT-0118.
[5] — Erro R, Bhatia KP, Edwards MJ, et al. Clinical diagnosis of propriospinal myoclonus is unreliable: an electrophysiologic study. Movement disorders : official journal of the Movement Disorder Society. 2013;28(13):1868-1873. DOI. PMID: 24105950. FND-CIT-0138.
[6] — van der Salm SM, Tijssen MA, Koelman JH, van Rootselaar AF. The bereitschaftspotential in jerky movement disorders. Journal of neurology, neurosurgery, and psychiatry. 2012;83(12):1162-1167. DOI. PMID: 22952323. FND-CIT-0125.
[7] — Beudel M, Zutt R, Meppelink AM, et al. Improving neurophysiological biomarkers for functional myoclonic movements. Parkinsonism & related disorders. 2018;51:3-8. DOI. PMID: 29653908. FND-CIT-0122.
[8] — Meppelink AM, Little S, Oswal A, et al. Event related desynchronisation predicts functional propriospinal myoclonus. Parkinsonism & related disorders. 2016;31:116-118. DOI. PMID: 27477621. FND-CIT-0137.
[9] — Malaty IA, Anderson S, Bennett SM, et al. Diagnosis and management of functional tic-like phenomena. Journal of Clinical Medicine. 2022;11(21):6470. Source. FND-CIT-0110.
[10] — Zutt R, Gelauff JM, Smit M, van Zijl JC, Stone J, Tijssen MAJ. The presence of depression and anxiety do not distinguish between functional jerks and cortical myoclonus. Parkinsonism & Related Disorders. 2017;45:90–93. DOI. Accepted manuscript. FND-CIT-0225.
[11] — Latorre A, Ganos C, Hamada M, et al. Diagnostic utility of clinical neurophysiology in jerky movement disorders: a review from the MDS Clinical Neurophysiology Study Group. Movement Disorders Clinical Practice. 2025;12(3):272–284. DOI. Full text. FND-CIT-0226.
[12] — Nicholson C, Edwards MJ, Carson AJ, et al. Occupational therapy consensus recommendations for functional neurological disorder. Journal of Neurology, Neurosurgery & Psychiatry. 2020;91(10):1037–1045. https://doi.org/10.1136/jnnp-2019-322281 FND-CIT-0011.

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