QUANTITATIVE NEEDLE ELECTROMYOGRAPHY (EMG) Simon Podnar, MD, DSc Institute of Clinical Neurophysiology Division of Neurology, UMC, Ljubljana
ELECTROMYOGRAPHY (EMG) Recording of muscle bioelectrical activity. Generators are muscle fibers. Types of electrodes: surface electrodes, concentric/monopolar needle electrodes, single fiber needle electrodes, macro-emg needle electrodes. Types of EMG: kinesiological EMG, motor unit EMG.
TYPES OF NEEDLE ELECTRODES
EQUIPMENT Standard concentric needle electrode. EMG system with facility of: template operated motor unit potential (MUP) analysis = multi-mup, turn/amplitude analysis of the interference pattern (IP) (cloud analysis). Ground electrode. Filters: 5 Hz - 10 khz. Sweep: 5-10 ms/division. Amplification: 200 µv - 2 mv /division.
QUANTIFICATION In clinical practice qualitative needle EMG is usually used, mainly because it is faster. Advantages of quantification: higher sensitivity and specificity, better reproducibility, easier comparison of results, possibility to produce reference data, possibility to cooperate between centers.
WHEN TO USE QUANTITATIVE EMG? Results of qualitative EMG are not clear. Follow up of patients with chronic neuromuscular diseases (e.g., myopathies, ALS, ). Need for exact documentation. Education. Research and development.
PHASES OF CONCENTRIC NEEDLE EMG EXAMINATION Observation of EMG activity in relaxed muscle. Observation and quantification of motor unit potentials (MUP) during slight muscle contraction. Observation and quantification of the interference pattern (IP) during different levels of muscle contraction.
BIOELECTRICAL ACTIVITY IN RELAXED MUSCLE klinični center ljubljana
BIOELECTRICAL ACTIVITY IN RELAXED MUSCLE klinični center ljubljana
QUANTIFICATION OF SPONTANEOUS DENERVATION ACTIVITY (SDA) No automatic method to quantify SDA is available. Two semi-quantitative methods exist: number of places with SDA (x/10), estimation of SDA quantity on different places (+, ++, +++).
GENERATION OF MOTOR UNIT POTENTIALS Stålberg and Trontelj, 1992
MOTOR UNIT POTENTIAL PARAMETERS klinični center ljubljana Podnar and Fowler, 2004
CONCENTRIC NEEDLE ELECTRODE Duration Concentric electrode Amplitude Spike Area Nandedkar, 1988 Monopolar electrode
MUP QUANTIFICATION Methods: manual-mup analysis (freezing), single-mup analysis (trigger and delay), multi-mup analysis (template). Results obtained by different methods differ separate normative data are needed.
MULTI-MUP ANALYSIS Conditions for MUP acceptance precisely standardized: negative phase amplitude: > 30 µv, rise time: > 300 µv/ms, firing frequency: > 1 Hz. Analysis of 4.8 s epochs. Analysis of 0-6 MUPs on each site. 20 MUPs in 5 min, + 3 min for editing.
REFERENCE VALUES Precise standardization enables world-wide cooperation in development of reference data. Reference values for: normal subjects, patients with individual neuro-muscualr diseases. Factors influencing MUP/IP reference values: studied muscle, analysis technique, activation level, age & sex.
Mean value klinični center ljubljana Standard deviation (z) Normal Pathologic -3-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 (z)
COMPARISON OF MUP PARAMETERS IN 3 MUSCLES
ROLE OF CONCENTRIC NEEDLE EMG Differentiation between normal, myopathic and neuropathic muscle, Help in localization of lesions (pattern of affected muscles). Help with determination of the mechanism of nerve lesion (demyelination, axonal lesion, neurotmesis). Determination of lesion age and progression. Demonstration of early reinnervation. Determination of severity and prognosis of injury.
PATHOLOGICAL MUP CHANGES Normal Neuropathy Myopathy Stålberg et al., 1996
Stålberg and Karlsson, 2001
Stålberg and Karlsson, 2001
Podnar and Vodušek, 2001
Podnar and Vodušek, 2001
Podnar and Mrkaić, 2002
Podnar, 2004
Podnar, 2004
Podnar and Zidar, 2006
Podnar and Zidar, 2006
MECHANISM OF MUP CHANGES Reduced amplitude / duration: muscle fiber atrophy, increased quantity of connective tissue and fat, increased motor end-plate jitter and blocking, Increased amplitude / duration: muscle fiber grouping, muscle fiber hypertrophy. Increased number of phases and turns: slow conduction in motor nerve terminal branches, increased diameter of the motor end-plate region, increased variability of the muscle fiber diameters.
INTERFERENCE PATTERN (IP)
IP QUANTIFICATION Fast and non-biased. Sensitivity and specificity lower than for MUP analysis. More difficult correlation between IP parameters and (path)ophysiology. Methods: spectral analysis, turn/amplitude ( cloud ) analysis.
Podnar et al., 2000
Podnar et al., 2002
SPECTRAL ANALYSIS Myopathy Normal Neuropathy Fuglsang-Frederiksen, 1990
VARIOUS QUANTITATIVE ANALYSES MUP T/A FA Firing Amplitude MUP + + - - Duration MUP + + + - Rise time MUP + - + - Complexity MUP + + + - Stability MUP + - - - Additional firing + - - - Density IP - + - - Early recruitment - - - + Central drive - + - + Fatigue - + + -
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