Transcript INFLAMMATORY MYOPATHIES
Myopathies and their Electrodiagnosis1
Randall L. Braddom, M.D., M.S. Clinical Professor Robert Wood Johnson Medical School and the New Jersey Medical School [email protected]
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
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
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
STEP III Isolate one motor unit, focus on it Study the MUAP Frequency of firing Amplitude Duration Phases
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
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 Potential
MUAP ANALYSIS
Rise Time
Dumitru recommends 0.5 msec. or less
Turns
Change in direction without baseline crossing
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
MUAP ANALYSIS
Myoneural Junction problems can cause
Variability in amplitude
Drop-out of MUAP’s
Five Steps of EMG
Step IV
Recruitment
Interference Pattern
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
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
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
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
Spontaneous firing of all or part of a motor unit
Denny-Brown and Pennypacker 1938
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
Spontaneous firing of a single muscle fiber
Best seen Step I 1-50 Hz Regular pattern
FIBRILLATIONS
Spontaneous oscillations in membrane potential of a denervated or injured muscle fiber Diphasic or triphasic with
initial positivity
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
FIBRILLATIONS
Most important factor
Regular rhythm
This separates them from end plate spikes and voluntary motor unit action potentials and fasciculations
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
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
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 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 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 Groups
Inflammatory
Muscle membrane irritability Rapid destruction of muscle fibers
Non-Inflammatory
Little muscle membrane irritability Slow destruction of muscle fibers
Myotonic
INFLAMMATORY MYOPATHIES
Muscle membrane irritability Usually involve myositis Examples: Dermatomyositis Polymyositis Trichinosis
NON-INFLAMMATORY MYOPATHIES
Few or no positive waves/fibrillations Often only slowly progressive Examples: FSH-MD Steroid Myopathy
MYOTONIC MYOPATHIES
All have the myotonic phenomenon Examples Myotonic dystrophy Myotonia congenita
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
INFLAMMATORY MYOPATHIES
These typically have High sedimentation rate High muscle enzymes Relatively acute history Rapid onset of weakness Toxic symptoms
5 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
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 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
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 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
Remember
STEROIDS QUIET MUSCLE MEMBRANES
EMG PIN CAN CAUSE PROBLEMS WITH MUSCLE BIOPSY