Myopathies and their Electrodiagnosis1Myopathies and their Electrodiagnosis1

Randall L. Braddom, M.D., M.S.

Clinical Professor

Robert Wood Johnson Medical School and the New Jersey Medical School

rlbraddom@comcast.net

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

THE FIVE STEPS OF EMG 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

THE FIVE STEPS OF EMG 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

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

THE FIVE STEPS OF EMG THE FIVE STEPS OF EMG

STEP III Isolate one motor unit, focus on it Study the MUAP

Frequency of firing Amplitude Duration Phases

MUAP ANALYSIS 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 MUAP’s analyzed will be Type I

Use wide band width filter: (at least 10-10,000 Hz)

MUAP ANALYSIS MUAP ANALYSIS

Amplitude (peak to peak) Duration Phases

# of baseline crossings plus one 5 or more phases is polyphasic 10-32% of MUAP’s are polyphasic

Motor Unit Action PotentialMotor Unit Action Potential

MUAP ANALYSIS MUAP ANALYSIS Rise Time

Dumitru recommends 0.5 msec. or less

Turns Change in direction

without baseline crossing

MUAP ANALYSIS MUAP ANALYSIS Satellite Potentials

Time locked (usually a few msec later) Normal: 10% of MUAP’s Myopathy: 45% of MUAP’s Neuropathic: Slightly more than normal Don’t include in MUAP duration Probably due to fiber splitting and slow

conduction along immature terminal sprouts

MEAN MUAP DURATIONS MEAN MUAP DURATIONS

MUAP ANALYSISMUAP ANALYSIS

Myoneural Junction problems can cause Variability in amplitude Drop-out of MUAP’s

Five Steps of EMGStep IV

RecruitmentInterference Pattern

RECRUITMENT Rule of Fives 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

RECRUITMENT RECRUITMENT Experienced EMG’ers 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 MUAP’s seen

Recruitment Examples Normal

Fastest potential is 20 Hz, 4 MUAP’s present Recruitment ratio is 5

MYOPATHIC Ratio Low: 4 or less

NEUROPATHIC Ratio High: Usually 10 or more

INTERFERENCE PATTERN 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

THE FIVE STEPS OF EMG 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)

FASCICULATIONS FASCICULATIONS

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

1938

FASCICULATIONS 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

FIBRILLATIONS FIBRILLATIONS Spontaneous

firing of a single muscle fiber

Best seen Step I 1-50 Hz Regular pattern

FIBRILLATIONS FIBRILLATIONS

Spontaneous oscillations in membrane potential of a denervated or injured muscle fiber

Diphasic or triphasic with initial positivity

FIBRILLATIONSFIBRILLATIONS 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

FIBRILLATIONS Most important factor

Regular rhythm This separates them from end plate

spikes and voluntary motor unit action potentials and fasciculations

GRADING FIBRILLATIONS 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

POSITIVE WAVES 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

POSITIVE WAVES POSITIVE WAVES Frequency 1-50 Hz Regular Sharp positive

deflection, then long negative phase

Duration 1-5 msec Amplitude to 1 mV “Thumping” sound

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

MYOPATHIC CHANGES 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

MYOTONIC DISCHARGES 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

EMG Separates Myopathies into Three GroupsEMG 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

INFLAMMATORY MYOPATHIESINFLAMMATORY MYOPATHIES

Muscle membrane irritability Usually involve myositis Examples:

Dermatomyositis Polymyositis Trichinosis

NON-INFLAMMATORY MYOPATHIESNON-INFLAMMATORY MYOPATHIES

Few or no positive waves/fibrillations

Often only slowly progressive Examples:

FSH-MD Steroid Myopathy

MYOTONIC MYOPATHIESMYOTONIC MYOPATHIES

All have the myotonic phenomenon Examples

Myotonic dystrophy Myotonia congenita

NON-INFLAMMATORY MYOPATHIESNON-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

INFLAMMATORY MYOPATHIESINFLAMMATORY MYOPATHIES

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

5 STEPS OF EMG5 STEPS OF EMG Slowly progressive myopathy

I: Normal II Normal III Reduced amplitude, duration of

MUAP’s IV Increased # of motor units firing per

strength of contraction Normal interference pattern

NCV’s usually normal

5 STEPS OF EMG 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

NCV’s typically normal except for reduced amplitude of the evoked potential in motor studies

MUAP CHANGES IN MYOPATHYMUAP 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

Myopathy’s Recruitment Change Myopathy’s Recruitment Change

Remember the “Rule of Fives” Determine frequency of fastest firing MUAP Divide by number of MUAP’s seen If fastest is at 20 Hertz and four are present,

recruitment ratio is 5 Myopathy typically has recruitment ratio

of 4 or less

Step III Problem in MyopathyStep 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 MUAP’s are weak, the patient

will tend to fire more than one at a time Hard for the patient to fire only one MUAP

RememberRemember

STEROIDS QUIET MUSCLE MEMBRANES

EMG PIN CAN CAUSE PROBLEMS WITH MUSCLE BIOPSY