3rd Congress of the European Academy of Neurology

Amsterdam, The Netherlands, June 24 – 27, 2017

Hands-on Course 8

MDS-ES/EAN: Neurophysiological study of tremor - Level 1

Orthostatic tremor, cortical tremor, dystonic tremor and psychogenic tremor: Electro-clinical

semiology

Emmanuelle Apartis Paris, France

Email: emmanuelle.apartis@sat.aphp.fr

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Conflict of interest: The author has no conflict of interest in relation to this manuscript.

Key learning objectives

The key learning objectives of the session are to identify the clinical and

electrophysiological core signs of uncommon tremors: orthostatic tremor,

cortical tremor, dystonic tremor and psychogenic tremor, in order to as-

sess an appropriate positive diagnosis and to differentiate them from

other movement disorders, thus leading to adequate care.

Essential knowledge

1. Orthostatic tremor

Primary orthostatic tremor (OT) is a rare disorder that remains under-

diagnosed. OT arises from a central generator located in the posterior

fossa with pathological ponto-cerebello-thalamo-cortical activations 1. OT

predominantly affects women over the age of 50. The cardinal symptoms,

which are highly suggestive of the diagnosis, are feelings of instability, leg

tremor in the standing position, improvement with walking and dis-

appearance while sitting. OT remains mis-diagnosed as vestibular or

cerebellar disorder or psychogenic balance disorder. Yet, the diagnosis of

OT can be very easily assessed by the recording of the typical tremor

activity in the 13-18 Hz range in the legs while standing. This char-

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acteristic electro-clinical picture differs from those of two looking alike

conditions - tremor in orthostatism and orthostatic myoclonus - frequently

related to neurodegenerative disorders and parkinsonian syndromes.

Signs of OT 2, 3:

- The symptoms appear a few seconds to a few minutes after

standing. They disappear when walking and when sitting at rest.

They are improved when supporting against a wall or a table.

- The major symptom of OT is the feeling of instability, even more

than tremor in the legs. No falls but fear of falling.

- At clinical examination, the tremor is hardly visible, and may be

palpable. The walk and the neurological examination are other-

wise normal.

- Neurophysiology: Very regular tremor of high frequency (13-14

Hz) evidenced in both legs when standing, disappearing at rest and

composed of very short synchronous EMG bursts (20-40 ms). The

higher the tremor amplitude on polymyography, the higher the

disability, both increasing with the duration of standing. Extension

of OT to the trunk and upper limb muscles when standing con-

tinues. High inter-limb and inter-muscular coherence at tremor

frequency.

Signs of tremor in orthostatism:

- Tremor is the major complaint, instability can be mild or absent

- Tremor involves one or two legs when standing

- Tremor is visible at clinical examination

- Tremor can persist when walking or at rest when sitting

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- Neurological examination may be abnormal - rigidity, akinesia,

cerebellar signs -

- Associated conditions : idiopathic Parkinson’s disease, hydroceph-

alus, spino-cerebellar ataxia, brainstem or cerebellar focal lesions,

advanced essential tremor

- Neurophysiology: Regular tremor at slower frequency (3-12 Hz)

than OT, with longer burst duration (70-130 ms) when standing.

Associated proximal or distal rest tremor in the lower limb at the

same frequency. Possibly, re-emergent parkinsonian tremor of the

lower limbs, with posture or when standing.

Signs of orthostatic myoclonus 4:

- Similar symptoms than OT, with frequent feeling of instability,

sometimes feeling of “ shaky-legs”, more than tremor.

- Persistence at walk, fear of falling and falls

- Neurological examination is frequently abnormal – rigidity, akine-

sia, cerebellar signs, cognitive signs

- Associated conditions: mainly idiopathic Parkinson’s disease, also

Lewy body dementia, Alzheimer’s disease, multiple system atro-

phy, progressive supra-nuclear palsy

- Neurophysiology: Irregular myoclonic bursts, in the lower limbs,

asynchronous, bursts duration (40 to 100 ms), frequency range (6-

11 per seconds), occurring predominantly when standing, some-

times persisting at walk or with outstretched legs. No inter-limb

coherence at a given frequency. The generator may be either

cortical or sub-cortical, depending on the underlying disease.

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2. Cortical tremor 5,6

Familial Cortical Myoclonic Tremor (FCMT) is a rare condition with an

action tremor to be distinguished from essential tremor, considering the

different therapeutic issues for both diseases. FCMT is an autosomal

dominant disease characterized by a slow or non-progressive adult-onset,

involuntary repetitive myoclonic jerks of the distal upper limbs, looking

like an irregular tremor enhanced by outstretched posture and action.

Progressive myoclonic epilepsy is excluded by the absence of ataxia and

mental retardation and by the benign course of the disease. In this back-

ground, the association of an upper limb postural tremor with generalized

epilepsia or a familial history of epilepsia, and its resistance to beta-

blockers should question this diagnosis, considering the good response of

FCMT to anti-epileptic drugs. Focal cortical tremor may also occur with

congenital or acquired lesions of the cortical fronto-central area. Electro-

physiological findings in FCMT and focal cortical tremor fulfil criteria for

cortical myoclonus.

Neurophysiology of FCMT:

- Irregular postural tremor recorded on the accelerometer (5-10 per

second)

- Brief polymyographic bursts lasting less than 50 ms in the distal

muscles

- Predominant at postural maintenance, absent at rest, not en-

hanced with intention

- Neurophysiological signs of cortical hyperexcitability and evidence

for a cortical generator of the myoclonus:

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o Giant cortical components of somato-sensory evoked po-

tentials (P25-N33>10 µV)

o Enhanced long-loop transcortical C-reflex (latency: 45-50 ms)

o Cortical focal transients preceding myoclonic jerks by 10-

25 ms, demonstrable by the EEG jerk-locked back aver-

aging method.

3. Dystonic tremor 7

Dystonic tremor is classically defined as tremor in a body part that is

affected by dystonia. Tremor is a common feature in patients with adult-

onset focal dystonia and may involve several different body parts - i.e.

cervical dystonic tremor, upper limb dystonic tremor, truncal tremor -.

Dystonic features may be severe but also mild. Dystonic tremor may also

be isolated, without overt clinical signs of dystonia 8. Dystonic tremor

should be distinguished from tremor that is associated with dystonia, i.e.,

that occurs in a body part not affected by dystonia. In addition to its

diagnosis value, neurophysiological recording can be helpful in assessing

the more active muscles and guiding the botulinum toxin injections when

dystonic tremor is highly focal;

Classical signs of dystonic tremor:

- Typically, postural or action tremor, rarely manifesting at rest

- Suppression by sensory tricks (“geste antagoniste”)

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- Clinical dystonic features in the same body part

o Abnormal posture

o Motor overflow defined as unintentional muscle contrac-

tion, affecting the electivity of a voluntary movement

- Tremor elicited by a specific task or a selective position of the

body part

- Neurophysiology:

o Irregular tremor, with variable duration (50-300 ms) and

amplitude of consecutive bursts

o Variable frequencies (3-12 Hz)

o Sustained contractions, spasms or myoclonus associated to

tremor

o Co-contraction of agonistic and antagonistic muscles (i.e.

wrist flexors and wrist extensors)

Special features of cervical dystonic tremor 9:

- In addition to the criteria mentioned above,

- Recording of the neck muscles allows comparing the activities of

the coupled muscles that rotate the head to the left - left splenius

and right sterno-cleido-mastoideus - to those that rotate the head

to the right - right splenius and left sterno-cleido-mastoideus - .

- An asymmetrical location of the tremor in rotator muscles or

elective involvement of one couple argues for dystonic cervical

tremor and against essential cervical tremor.

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Signs of pure writing tremor:

- Regular or irregular tremor occurring specifically with writing

- Disappearance of tremor during postural maintenance, during non-

specific actions and other tasks than writing

- Mirror writing tremor elicited at rest by writing with the contra-

lateral hand

- Lack of overt dystonic features in the affected hand

3. Psychogenic tremor

Psychogenic tremor frequently involves the upper limbs, but may affect

every part in the body including neck, legs and trunk. It may occur

under different conditions, rest, posture, action, intention, and even

with orthostatism. After evidence of the clinical clues suggestive of

psychogenic tremor, neurophysiological tools are necessary to assess the

diagnosis by revealing objective positive signs in comparison to the

classical characteristics of tremors of organic origin. Psychogenic tremor

should be distinguished chiefly from pyramidal clonus and organic tremors

such as enhanced physiologic tremor, parkinsonian tremor, dystonic trem-

or, and odd tremors. In some cases, these physiological data combined

with the patient insight during the tests, are beneficial in persuading the

patients of the accuracy of the diagnosis and of the potential reversibility

of their symptoms.

Clinical clues for psychogenic tremor:

- Tremor with a sudden onset

- Tremor with a variable course, periods of complete normality

- Distractibility

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- Fluctuations of intensity, or sudden shifts of the localization or

the axis of tremor, particularly if they are provoked by external

manipulations (i.e., passive immobilization of the hand inducing

the shifting of tremor to the shoulder or to another body part)

- Inconsistencies

Neurophysiological signs of psychogenic tremor 10,11:

Among criteria listed by R Helmich (part 1 of the HoC: Neurophysiological

study of tremor: how to do it in clinical practice), the strongest are

related to the tremor frequency analysis and manipulation by the

examiner:

- The spontaneous variability of tremor frequency

- The frequency driving induced by contralateral rhythmic tasks,

By contrast, organic tremors have a stable frequency that cannot be

driven to another one. Tips and tricks adapted to the body part affected

by the psychogenic tremor, and pitfalls in tremor variability assessment

and interpretation will be highlighted, with a special attention paid to the

differential diagnosis of dystonic tremor.

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References and suggested reading:

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Brandt T, Strupp M, Dieterich M, Zwergal A. Pathological ponto-

cerebello-thalamo-cortical activations in primary orthostatic

tremor during lying and stance. Brain. 2017 Jan;140:83-97.

2. Ganos C, Maugest L, Apartis E, Gasca-Salas C, Cáceres-Redondo MT,

Erro R, Navalpotro-Gómez I, Batla A, Antelmi E, Degos B, Roze E,

Welter ML, Mestre T, Palomar FJ, Isayama R, Chen R, Cordivari C,

Mir P, Lang AE, Fox SH, Bhatia KP, Vidailhet M. The long-term

outcome of orthostatic tremor. J Neurol Neurosurg Psychiatry.

2016;87(2):167-72.

3. Hassan A, Ahlskog JE, Matsumoto JY, Milber JM, Bower JH,

Wilkinson JR. Orthostatic tremor: Clinical, electrophysiologic,

and treatment findings in 184 patients. Neurology. 2016 Feb

2;86(5):458-64.

4. Gasca-Salas C, Arcocha J, Artieda J, Pastor P. Orthostatic

myoclonus: an underrecognized cause of unsteadiness?

Parkinsonism Relat Disord. 2013 Nov;19(11):1013-7.

5. Ikeda A, Kakigi R, Funai N, Neshige R, Kuroda Y, Shibasaki H.

Cortical tremor: a variant of cortical reflex myoclonus.

Neurology. 1990;40(10):1561-

6. Striano P, Zara F. Autosomal dominant cortical tremor, myoclonus

and epilepsy. Epileptic Disord. 2016;18(2):139-144.

7. Defazio G, Conte A, Gigante AF, Fabbrini G, Berardelli A.

Is tremor in dystonia a phenotypic feature of dystonia?

Neurology. 2015 Mar 10;84(10):1053-9. Review.

8. Gövert F, Deuschl G. Tremor entities and their classification:

an update. Curr Opin Neurol. 2015;28(4):393-9.

9. Deuschl G, Heinen F, Kleedorfer B, Wagner M, Lücking CH,

Poewe W. Clinical and polymyographic investigation of

spasmodic torticollis. J Neurol. 1992;239(1):9-15.

10. Apartis E. Clinical neurophysiology of psychogenic movement

disorders: how to diagnose psychogenic tremor and myoclonus.

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