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Myopathies and their Electrodiagnosis1

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Myopathies and their Electrodiagnosis1 Randall L. Braddom, M.D., M.S. Clinical Professor Robert Wood Johnson Medical School and the New Jersey Medical School – PowerPoint PPT presentation

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Title: Myopathies and their Electrodiagnosis1

1
Myopathies and their Electrodiagnosis1

Randall L. Braddom, M.D., M.S.
Clinical Professor
Robert Wood Johnson Medical School and the New
Jersey Medical School
rlbraddom_at_comcast.net

2
The Five Steps of EMG

First published by Johnson and Melvin in 1971.
Johnson EW, Melvin JL. Value of electromyography
in lumbar radiculopathy. Arch Phys Med Rehabil
(June) 1971. 52 239-243

3
THE FIVE STEPS OF EMG

STEP I (muscle at rest)
Put the pin in the muscle
Sit back, relax
Watch for spontaneous potentials
Fibrillations, Fasciculations, Complex Repetitive
Discharges, Myotonic Potentials

4
THE FIVE STEPS OF EMG

STEP II (insertional activity)
Insert the pin with quick, one mm. movements
Baseline should be quiet when needle stops
Insertional Activity lasts about 50 msec.
After the movement noise, watch for
Positive Waves
All Spontaneous Potentials

5
GRADING INSERTIONAL ACTIVITY

NORMAL
Easy to find, lasts 50 msec.
DECREASED
Hard to find, usually due to muscle loss
INCREASED
Easy to find, lasts longer than 50 msec.
Some include positive waves, fibs, etc

6
THE FIVE STEPS OF EMG

STEP III
Isolate one motor unit, focus on it
Study the MUAP
Frequency of firing
Amplitude
Duration
Phases

7
MUAP ANALYSIS

Only a few fibers near the pin produce the
amplitude (2-12 fibers within 0.5 mm)
The fibers distant from the pin produce the early
and late components of the duration
Due to Henneman size principle, almost all MUAPs
analyzed will be Type I
Use wide band width filter (at least 10-10,000
Hz)

8
MUAP ANALYSIS

Amplitude (peak to peak)
Duration
Phases
of baseline crossings plus one
5 or more phases is polyphasic
10-32 of MUAPs are polyphasic

9
Motor Unit Action Potential
10
MUAP ANALYSIS

Rise Time
Dumitru recommends 0.5 msec. or less
Turns
Change in direction without baseline crossing

11
MUAP ANALYSIS

Satellite Potentials
Time locked (usually a few msec later)
Normal 10 of MUAPs
Myopathy 45 of MUAPs
Neuropathic Slightly more than normal
Dont include in MUAP duration
Probably due to fiber splitting and slow
conduction along immature terminal sprouts

12
MEAN MUAP DURATIONS
13
MUAP ANALYSIS

Myoneural Junction problems can cause
Variability in amplitude
Drop-out of MUAPs

14
Five Steps of EMG

Step IV
Recruitment
Interference Pattern

15
RECRUITMENT Rule of Fives

Isolate one MUAP
Begins at 3 Hz and can fire in stable manner at
5-7 Hz
Note firing frequency of first potential when
second one begins...usually 10 Hz
Freeze the screen and measure time between the
two potentials (recruitment interval) (usually
100 msec, corresponding to 10 Hz)
The second potential appears firing at 5 Hz
Third potential appears when first is at 15 Hz
and second at 10 Hz

16
RECRUITMENT

Experienced EMGers can hear this
Easy quantitative method
Freeze the screen with a number of motor units
firing
Determine frequency of fastest firing MUAP
Divide by the number of MUAPs seen

17
Recruitment Examples

Normal
Fastest potential is 20 Hz, 4 MUAPs present
Recruitment ratio is 5
MYOPATHIC
Ratio Low 4 or less
NEUROPATHIC
Ratio High Usually 10 or more

18
INTERFERENCE PATTERN

Ask the patient to maximally recruit the muscle
Watch for
Holes in the Interference Pattern
Amplitude of the Interference Pattern
Observe the frequency of firing to make sure you
are seeing a maximal effort by the patient

19
THE FIVE STEPS OF EMG

STEP V The Cerebral Step
Put together all the steps to reach conclusions
Do the findings support your clinical hypothesis?
Determine how to proceed from this point in the
study (Dynamic rather than protocol approach)

20
FASCICULATIONS

Spontaneous firing of all or part of a motor unit
Denny-Brown and Pennypacker 1938

21
FASCICULATIONS

Step I (Muscle at Rest)
Irregularly Irregular
Origin anywhere in the lower motor neuron
Usually look like polyphasic MUAP, but can be any
size and shape
Often normal, but also common in anterior horn
cell disease

22
FIBRILLATIONS

Spontaneous firing of a single muscle fiber
Best seen Step I
1-50 Hz
Regular pattern

23
FIBRILLATIONS

Spontaneous oscillations in membrane potential of
a denervated or injured muscle fiber
Diphasic or triphasic with initial positivity

24
FIBRILLATIONS

1-5 msec duration
20-1000 uV amplitude
Can be initially negative near end plates
Usually indicate denervation, but occur with any
muscle membrane irritability
Tick or sound like rain on a tin roof

25
FIBRILLATIONS

Most important factor
Regular rhythm
This separates them from end plate spikes and
voluntary motor unit action potentials and
fasciculations

26
GRADING FIBRILLATIONS

0 None (or isolated fib)
1 Found in at least two muscle regions
2 Moderate found in three muscle regions
3 Many in all muscle areas tested
4 Baseline obliterated by fibrillations

27
POSITIVE WAVES

Same as Fibrillation
Recorded by pin next to muscle fiber
Seen best in Step II
Due to muscle membrane irritability, often
because of denervation

28
POSITIVE WAVES

Frequency 1-50 Hz
Regular
Sharp positive deflection, then long negative
phase
Duration 1-5 msec
Amplitude to 1 mV
Thumping sound

29
Positive Waves and Fibs

New Trend in nomenclature
They are both the same thing
The shape is the only difference
Some now calling both fibrillations
Positive waves now called fibrillations with
positive wave shape

30
MYOPATHIC CHANGES

Decreased amplitude
Decreased duration
Increased number of phases
Increased of motor units firing per strength of
contraction
Some refer to this as increased recruitment

31
MYOTONIC DISCHARGES

Wax and Wane in frequency and amplitude
20-80 Hz
Two types can resemble fibrillations or positive
waves
Due to repetitive discharges of single muscle
fibers

32
EMG Separates Myopathies into Three Groups

Inflammatory
Muscle membrane irritability
Rapid destruction of muscle fibers
Non-Inflammatory
Little muscle membrane irritability
Slow destruction of muscle fibers
Myotonic

33
INFLAMMATORY MYOPATHIES

Muscle membrane irritability
Usually involve myositis
Examples
Dermatomyositis
Polymyositis
Trichinosis

34
NON-INFLAMMATORY MYOPATHIES

Few or no positive waves/fibrillations
Often only slowly progressive
Examples
FSH-MD
Steroid Myopathy

35
MYOTONIC MYOPATHIES

All have the myotonic phenomenon
Examples
Myotonic dystrophy
Myotonia congenita

36
NON-INFLAMMATORY MYOPATHIES

From an EMG standpoint, non-inflammatory merely
means that the electrical membranes are
sufficiently stable that there are no
Fibrillations
Positive Waves
Motor units will look myopathic

37
INFLAMMATORY MYOPATHIES

These typically have
High sedimentation rate
High muscle enzymes
Relatively acute history
Rapid onset of weakness
Toxic symptoms

38
5 STEPS OF EMG

Slowly progressive myopathy
I Normal
II Normal
III Reduced amplitude, duration of
MUAPs
IV Increased of motor units firing per strength
of contraction
Normal interference pattern
NCVs usually normal

39
5 STEPS OF EMG

Rapidly progressive myopathy
Step I Reduced and Fibrillations
Step II Positive Waves, Fibrillations
Step III Reduced amplitude, duration
Step IV Increased of motor units firing per
strength of contraction
NCVs typically normal except for reduced
amplitude of the evoked potential in motor
studies

40
MUAP CHANGES IN MYOPATHY

Shorter duration
Due to less contribution from distant fibers of
same motor unit
Lower amplitude
Less contribution from fibers close to the pin
Polyphasic
Less integrated potential due to drop out of some
fibers

41
Myopathys Recruitment Change

Remember the Rule of Fives
Determine frequency of fastest firing MUAP
Divide by number of MUAPs seen
If fastest is at 20 Hertz and four are present,
recruitment ratio is 5
Myopathy typically has recruitment ratio of 4 or
less

42
Step III Problem in Myopathy

Major Clue that myopathy might be present
When doing Step III, it will be difficult to
isolate a single MUAP
Since all are MUAPs are weak, the patient will
tend to fire more than one at a time
Hard for the patient to fire only one MUAP

43
Remember