Functional Tremor: Diagnostic Technique Inventory

Diagnostic techniques at a glance

Variability

The clinician compares tremor frequency, direction and distribution across tasks; marked changes can support a functional pattern. Variability alone is nonspecific. Instrumented time–frequency analysis has primary research support, but findings must be interpreted with the complete examination. [3][4]

Distractibility

Tremor decreases, pauses or changes during another motor or mental task. This is a positive comparison when the change is clear and clinically meaningful. Attention affects other tremors too; neither absence of distraction benefit nor one change settles the diagnosis. [4][5]

Entrainment

While the other hand taps a rhythm, the tremor adopts that rhythm. This may support functional tremor. Mechanical transmission and mirror movements can imitate coupling; some functional tremors suppress instead of entraining. Coherence testing can clarify the relationship. [5][6][7]

Tapping performance

The clinician checks whether the less affected hand can maintain several requested tapping rates while tremor is recorded. Abnormal performance contributes to a studied battery, but poor comprehension or coordination can also impair tapping. It is not independently diagnostic. [4][5]

Ballistic-movement interruption

A brief rapid movement of one limb is compared with tremor in the other. A simultaneous pause is supportive in context. The original study and later batteries support this comparison; it is not present in every functional tremor. [5][8]

Tonic coactivation at onset

Surface EMG may record a brief period of opposing-muscle activation before rhythmic tremor starts. This laboratory observation contributes to diagnosis. It differs from simply feeling a tense arm, and the battery’s accuracy does not apply to this component alone. [4][9]

Loading response

A specialist compares recorded tremor with and without a safe added load. An increase in amplitude can be supportive, but overlapping responses occur in other tremors. This is one battery component, not an instruction to add weights at home. [4][5]

Interlimb coherence

Recordings test whether two trembling limbs share a closely linked rhythm. This can support functional tremor, but orthostatic tremor and mechanically transmitted movement are important exceptions. It requires signal analysis and appropriate comparators. [4][10]

Wavelet coherence analysis

Time-varying signal analysis examines coupling that ordinary averaged coherence may miss. A diagnostic study suggests additional discrimination among tremor types. It remains a specialist method; its proposed thresholds need interpretation within the studied protocol. [11]

Combined electrophysiological battery

EMG and movement sensors combine tapping, entrainment or suppression, coactivation, loading, ballistic response and coherence. Development and prospective validation studies support the combined score. Accuracy belongs to that complete protocol and population, not to each sign or every mixed tremor. [4][5]

Whack-a-mole sign

Movement may become more apparent elsewhere when one affected body part is steadied. Later blinded assessment found limited sensitivity and imperfect specificity. This is an optional specialist observation; forceful restraint or deliberate symptom escalation is inappropriate. [12]

Suggestibility

Symptoms may change after a clinician’s suggestion or sensory cue. Small descriptive reports exist, but suggestion is not specific to FND. Transparent explanation and consent are essential; deceptive or painful provocation is not justified for this observation. [13]

Research and Sources

Citation	Figure	Full citation
[1]	—	Bartl M, Kewitsch R, Hallett M, Tegenthoff M, Paulus W. Diagnosis and therapy of functional tremor: a systematic review illustrated by a case report. Neurological Research and Practice. 2020;2:35. FND-CIT-0019. https://doi.org/10.1186/s42466-020-00073-1
[2]	—	Espay AJ, Aybek S, Carson A, et al. Current concepts in diagnosis and treatment of functional neurological disorders. JAMA Neurology. 2018;75(9):1132–1141. FND-CIT-0002. https://doi.org/10.1001/jamaneurol.2018.1264
[3]	—	O’Suilleabhain PE, Matsumoto JY. Time-frequency analysis of tremors. Brain : a journal of neurology. 1998;121 ( Pt 11):2127-2134. DOI. PMID: 9827772. FND-CIT-0175.
[4]	—	Schwingenschuh P, Katschnig P, Seiler S, et al. Moving toward “laboratory-supported” criteria for psychogenic tremor. Movement disorders : official journal of the Movement Disorder Society. 2011;26(14):2509-2515. DOI. PMID: 21956485. FND-CIT-0177.
[5]	—	Schwingenschuh P, Saifee TA, Katschnig-Winter P, et al. Validation of “laboratory-supported” criteria for functional (psychogenic) tremor. Movement disorders : official journal of the Movement Disorder Society. 2016;31(4):555-562. DOI. PMID: 26879346. FND-CIT-0178.
[6]	—	McAuley J, Rothwell J. Identification of psychogenic, dystonic, and other organic tremors by a coherence entrainment test. Movement disorders : official journal of the Movement Disorder Society. 2004;19(3):253-267. DOI. PMID: 15022179. FND-CIT-0135.
[7]	—	Merchant SH, Haubenberger D, Hallett M. Mirror movements or functional tremor masking organic tremor. Clinical neurophysiology practice. 2018;3:107-113. DOI. PMID: 30215019. FND-CIT-0154.
[8]	—	Kumru H, Valls-Solé J, Valldeoriola F, et al. Transient arrest of psychogenic tremor induced by contralateral ballistic movements. Neuroscience letters. 2004;370(2-3):135-139. DOI. PMID: 15488310. FND-CIT-0121.
[9]	—	Deuschl G, Köster B, Lücking CH, Scheidt C. Diagnostic and pathophysiological aspects of psychogenic tremors. Movement disorders : official journal of the Movement Disorder Society. 1998;13(2):294-302. DOI. PMID: 9539344. FND-CIT-0176.
[10]	—	Raethjen J, Kopper F, Govindan RB, et al. Two different pathogenetic mechanisms in psychogenic tremor. Neurology. 2004;63(5):812-815. DOI. PMID: 15365128. FND-CIT-0128.
[11]	—	Kramer G, Van der Stouwe AMM, Maurits NM, et al. Wavelet coherence analysis: A new approach to distinguish organic and functional tremor types. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 2018;129(1):13-20. DOI. PMID: 29136548. FND-CIT-0182.
[12]	—	Lagrand TJ, Brusse-Keizer M, Charmley A, et al. A Critical Appraisal of the Whack-a-Mole and Swivel Chair Signs in the Diagnosis of Functional Movement Disorders. Movement disorders clinical practice. 2024;11(1):63-68. DOI. PMID: 38291841. FND-CIT-0181.
[13]	—	Saranza G, Vargas-Mendez D, Lang AE, Chen R. Suggestibility as a valuable criterion for laboratory-supported definite functional movement disorders. Clinical neurophysiology practice. 2021;6:103-108. DOI. PMID: 33869904. FND-CIT-0170.