dr prashant shringi DM neurology resident

1. ELECTROPHYSIOLOGICAL EVALUATION
OF TREMORS MYOCLONUS DYSTONIA
Dr Prashant Shringi
Senior Resident
Neurology

2. • Tremor
• Myoclonus
• Dystonia
• Types of involuntary movements

3. Tremor
• Definiton:
• Tremor is defined as a rhythmical, involuntary oscillatory
movement of a body part

5. Neurophysiological characterstics of
tremors
• Source/Morphology
• Sound on Loudpeaker
• Stability
• Firing Rate
• Firing Pattern
• Motor unit (motor
neuron/axon)
• Marching soldiers
• Rising and falling
amplitude
• 1–5 Hz (interburst)
• Bursting –
• Synchronous bursting of
many different motor unit
potentials

6. Electrophysiological assesment of tremors
• Neurological examination reveals information regarding
frequency, regularity, amplitude and activation conditions
• Electrophysiological investigations help in confirming the
tremor, in differentiating it from other hyperkinetic
disorders like myoclonus, and may provide etiological
clues

7. What does neurophysiology add?
• A neurophysiological tremor assessment can quantify
certain tremor features that are not visible to the clinical
eye.
• Tremor frequency (as well as the stability of tremor
frequency over time) .
• Coherence - (which is the phase coupling between two
separate tremors, indicative of a common generator).

8. • Neurophysiological tremor assessment can provide
meaningful answers are: -
 Is the tremor of peripheral origin, central origin, or both?
 Are there objective signs of psychogenic tremor?
What is the tremor frequency and what is the pattern of
EMG activity associated with the tremor?

9. • Routine tremor assessment involves accelerometry of the
tremulous limb (often the arms) .
• Electromyography (EMG) measurements of the involved
muscles (often wrist extensor and flexor muscles).

10. • Accelerometry measures the movement of the limb, while
EMG measures the pattern of muscle activity that may
underlie these movements.

11. • Standard measurements:
Tremor at rest (preferably lying down on a bed), during
posturing, during actions, sometimes during standing
(orthostatic tremor)
Tremor under specific conditions (cognitive co-activation,
motor co-activation)
Tremor during loading of the limb (with 500 gm)
Tremor during ballistic movements with the tremulous
limb and with another limb

12. • Fourier analysis:
• Fourier analysis is useful to quantify amplitude and
frequency of tremors.
• Holmes’ tremor and primary orthostatic tremor, the
frequency is a most valuable diagnostic tool.

13. • Graphic tablet analysis:
• Analysis of writing tremor and to measure the extent of
action and intention tremor.

14. • Signs of peripheral tremor:
Tremor is confined to accelerometry (no EMG bursts)
Tremor frequency is reduced with loading of the limb (i.e.
adding a 500 g weight)
Tremor frequency depends on the length of the reflex arc
(e.g. higher in the finger than in the hand)

15. • Signs of enhanced physiological tremor:
>90% of enhanced physiological tremors have a
peripheral origin
Frequency > 6 Hz
Tremor variability (usually >1.75 Hz)

16. • Signs of psychogenic tremor :
Entrainment of the tremor rhythm during rhythmic
voluntary movement of another limb
Distractibility
Extreme variability of tremor frequency (usually > 1.75
Hz)
Pause or >50% reduction in tremor amplitude during a
ballistic movement of the contralateral limb (positive
pointing test)

17. Coherence of bilateral tremors (suggesting a common
oscillator, in this case the voluntary motor system)
Increased tremor amplitude during loading of the limb

18. • Signs of ET
Rhythmic bursts of postural tremor on EMG
Tremor frequency greater than or equal to 4 Hz
Absence of latency from rest to postural position

19. Presence of intention tremor
Changes of the dominant frequency peak less or equal to
1 Hz after the weight load test

20. • Signs of the classical Parkinson’s tremor :
Asymmetric resting tremor of the limb at a frequency of 4-
6 Hz
 Pill-rolling aspect
Transient (>2 sec) suppression of tremor amplitude during
a voluntary movement with the trembling arm

21. Increase in tremor amplitude during cognitive co-
activation or motor co-activation with another limb (e.g.
tapping with the contralateral hand, or walking)

22. • Tremor is recognized as a synchronous bursting pattern
of MUAPs separated by relative silence
• As multiple MUAPs fire simultaneously, the morphology of
individual MUAPs may be difficult to assess, and there
appears to be increased polyphasia.

23. • When tremor occurs at rest (e.g., Parkinson’s disease),
the spontaneous bursting discharge may be mistaken for
myokymic discharges.

24. • Myokymic discharges and tremor both result in a bursting
pattern of MUAPs,
• Major difference is that in myokymia the same MUAP
fires repetitively in a burst, whereas in tremor the burst is
composed of man different MUAPs.

25. • Also, if freezes the screen and looks closely at the burst,
one can see that the amplitude often will rise and fall in
tremor, whereas it remains relatively unchanged in
myokymia.

27. Myoclonus
• Myoclonus, one of the most commonly encountered
involuntary movements,
• -Characterized by sudden, brief, jerky, shock-like
movements involving the extremities, face, and trunk,
without loss of consciousness.

28. CLASSIFICATION OF MYOCLONUS
• Myoclonus can be classified into three groups-
Cortical
Subcortical
spinal

29. Silent features

30. • Electrophysiological studies are useful in the evaluation of
myoclonus -
Confirming the clinical diagnosis
• Understanding the underlying physiological mechanisms

32. • Myoclonic jerks are believed to be caused by
hyperexcitability of a group of neurons in certain cerebral
structures
• Relatiolationship of myoclonic jerks with EEG activity is of
primary importance in the study of myoclonus.

33. EEG CORRELATES OF MYOCLONUS
• Simultaneous recording of EEG and EMG is basic yet
important for the clinical study of any kind of myoclonus.
• Recording of the EEG– EMG polygraph before carrying
out more sophisticated investigations is most effective and
time-saving
• because the polygraph reveals which muscles are most
commonly involved by the myoclonic jerks of interest

34. • Myoclonic jerks of cortical origin are characterized by an
extremely short duration of the EMG correlates, usually
less than 50 ms
• Subcortical origin (except reticular reflex myoclonus)
have EMG correlates of much longer duration.

35. • Recording of its EMG correlates confirms the clinical
impression.
 Resting condition
 Also during isometric contraction of the corresponding
muscles
most commonly from wrist extensor muscles while the
wrists are maintained in extended position.

36. • EEG can be recorded from electrodes placed mainly over
the central areas, using either a bipolar or referential
derivation with earlobe reference

39. • Cortical myoclonus, EEG usually shows multifocal or
generalized spike-and-wave or multiple spike-and-wave
discharges with or without associated myoclonus
• Negative myoclonus of cortical origin may also be
associated with an EEG spike or spike-and-wave complex

40. • SSPE, the involuntary movement is constantly
associated with periodic, high-amplitude EEG discharges
of stereotyped waveform.
• Essential myoclonus and dystonic myoclonus are not
associated with any EEG abnormality.

41. JERK-LOCKED BACK AVERAGING
• Jerk-locked back averaging is essentially an extension of
the EEG–EMG polygraph,
• Principle is to back average the simultaneously recorded
EEGs with respect to myoclonus.

42. • Recording can be done with the patient placed either in
the sitting, reclining, or supine position, depending on the
patient’s condition.
• Surface EMGs are recorded by using exactly the same
method as used for recording with the EEG–EMG
polygraph.

43. • This technique is used to study the precise interval from
the EEG activity to the myoclonus as well as to study the
scalp distribution of the myoclonus-related EEG activity
based on simultaneous multichannel recordings.
• Epilepsia partialis continua is a good clinical indication for
applying this technique

44. CORTICO-MUSCULAR COHERENCE
• Based on the simultaneous recording of EEG and EMG
while myoclonic jerks in question are frequently occurring
• Expressed as a correlation of rhythmic activities of certain
frequency bands between EEG and EMG.

45. • By applying this analysis method to patients with cortical
myoclonus, Brown and colleagues found an abnormally
increased coherence for a much higher frequency range.

46. • Advantage:
• Contrast to the conventional method of jerk-locked back
averaging, which requires averaging of a considerable
number of sweeps , takes a relatively long time this
analysis method can be applied to a relatively short
segment of the EEG–EMG polygraph.

47. EVOKED RESPONSES
• For recording SEPs, the conventional method is-
• Electrical shocks are delivered to the median nerve at the
wrist as a square-wave pulse of 0.2– 0.5 ms duration at a
rate of 1–2Hz.
• Stimulus strength is adjusted to 10%–15% above the
motor threshold,

48. • In most patients with cortical reflex myoclonus, the SEP to
electrical stimulation of the peripheral nerve shows a
characteristic waveform,
• Main feature being an extreme enlargement of early
cortical components

49. • Since the giant SEP is not seen in other types of
myoclonus, its demonstration is clinically significant for
supporting the clinical diagnosis of cortical or cortical
reflex myoclonus.

50. Giant somatosensory
evoked potentials (SEPs)
and surface
electromyogram (EMG)
silent periods induced by
electrical
stimulation of the left
median nerve (LMN) at
wrist during the sustained
wrist extension in the
same patient as shown in
Figure 9. A single
sweep record. Note that
the giant SEP is seen not
only over the contralateral
central (C4) and parietal
(P4) electrodes (N35c) but
also
over the ipsilateral central
(C3) electrode (N35i)
about 15 ms later

51. LONG-LOOP REFLEX
• Long-latency, long-loop reflex can be recorded using the
same EMG electrode placement as used for jerk-locked
back averaging.
• Electrical shocks delivered to the median nerve at the
wrist are most commonly used.
• EMG response is best recorded from the thenar muscle
of the stimulated hand.

52. • Results:
• In cortical reflex myoclonus, a markedly enhanced long-
latency reflex is usually recorded from the thenar muscle
at a latency of around 45 ms after stimulation of the
median nerve at the wrist.

53. PAIRED STIMULATION EVOKED POTENTIALS
AND
LONG-LOOP REFLEX
• By employing a paired median nerve stimulation SEP
technique with various ISIs in a patient with cortical reflex
myoclonus, Dawson found a depression of cortical
excitability at a latency between 10 and 30 ms,
enhancement between 60 and 100 ms, and then another
depression.

54. TRANSCRANIAL MAGNETIC
STIMULATION
• Excitability change of the sensorimotor cortex is involved
in many cases of cortical or cortical reflex myoclonus as
its physiological background
• TMS is especially useful for directly investigating the
excitability change of the motor cortex.

55. • Reutens and colleagues applied TMS preceded by
electrical stimulation of the median nerve at various
intervals to patients with PME and found increased
excitability at approximately 50 ms after the peripheral
nerve stimulation.

56. Neuro physiologic characteristics of
myoclonus
• CORTICAL MYOCLONUS:
1) Associated EMG discharge of very short duration
(usually less than 50 ms)
2) Synchronous antagonists activity
3) EEG correlate
4) Enlargement of early component of SEP , often
accompanied by enhanced long-latency
5) EEG spike preceding the myoclonus by a short interval
(20 ms in case of hand myoclonus).

57. Subcortical-reticular myoclonus:
1) Myoclonic jerks are brief, lasting between 10-30 ms.
2) Cortical EEG correlates, if present, is not time-locked to
the EMG event,
3) SEP is not enlarged
4) Sequence of activation of muscles is different (up the
brainstem and down the spinal cord) ,Trapezius is
activated first, suggesting an origin at the level of
medulla

58. • Segmental and spinal myoclonus:
 May be uni or bilateral
 May be associated with contraction of external ocular
muscles, those of larynx, neck, diaphragm, trunk and
limb,
 Rhythm of 2 Hz (range 80–180/min)
NO EEG correlates and the SEPs are not enlarged.

59. Dystonia
Syndrome characterized by sustained or intermittent
involuntary muscle contractions, leading to debilitating
abnormal postures and twisting movements

60. • Primary dystonia is the commonest form of dystonia.
• Cervical dystonia (CD), the most common form of primary
dystonia.

61. • Abnormal twisting movements of dystonia are
characterized by co-contraction of agonist and antagonist
muscles.
• Voluntary movement exacerbates the co-contraction of
antagonist muscle pairs.

64. • In dystonia the EMG bursts are usually prolonged, and as
a consequence the agonist and antagonist activities may
overlap in time for a longer period than normal (co-
contraction)

66. H-Reflex
Striking co-contraction of agonists and antagonists that is
so typical of dystonia suggests a breakdown of the normal
pattern of reciprocal innervation between opposing
muscles.
• Reciprocal inhibition of H reflexes in forearm flexor
muscles can be demonstrated by stimulation of forearm
extensor muscle afferents in the radial nerve

67. In normal subjects consists of an initial short-lasting
disynaptic Ia inhibitory phase (Day et al., 1984) , a longer-
lasting phase which is produced by presynaptic inhibition
of large proprioceptive afferent fibres (Berardelli et al.,
1987).
Studies in patients with writer’s cramp showed that there is
a reduction in the amount of inhibition in both the early and
late phases of reciprocal inhibition

68. Blink reflexes
• Electrical stimulation of the supraorbital nerve .
• In primary cranial dystonia, the initial short-latency
ipsilateral R1 response is normal, but the later bilateral R2
component of the blink reflex is larger and longer-lasting
than normal and its recovery cycle to paired supraorbital
nerve stimuli is enhanced

69. • Neural pathway of the blink reflex is intact in dystonia, but
that the excitability of brainstem inter neuronal pathways
mediating the R2 component of the response is
enhanced.

71. EEG and Dystonia

73. Conclusion
Electrophysiogiological studies used for to confirm diagnosis .
Used to ascertain pathophysiology and etiology of disease.
Used for clinical corelation between cortical discharges and jerks.

74. Refrrences
• Electrophysiologic Assessments of Involuntary Movements: Tremor
and Myoclonus, park et al,J Mov Disorder. 2009 May; 2(1): 14–17.
• Electrophysiological studies of myoclonus , hiroshi et al:Muscle Nerve
31: 157–174, 2005
• Pathophysiology of primary dystonia A. Berardelli,etal, Brain (1998),
121, 1195–1212
• Neurophysiological study of tremor: How to do it in clinical
practice:Rick Helmich; 3rd Congress of the European Academy of
Neurology Amsterdam, The Netherlands, June 24 – 27, 2017
• Bradley’s Neurology in clinical practice 7th edition
• Electromyography and Neuromuscular Disorders shapiros et al 3rd
edtion

75. • THANK YOU