This document provides an overview of electrodiagnosis techniques including NCV/EMG. It discusses using these tests to assess sensory and motor function as well as evaluate conditions like radiculopathy, neuropathy, and myopathy. Specific techniques are described like analyzing CMAPs and SNAPs to identify denervation, conduction block, and demyelination. EMG techniques like evaluating spontaneous activity, insertional activity, and motor unit action potentials are covered to assess muscle health and innervation. The document provides details on interpreting electrodiagnostic results to localize issues and characterize conditions as acute vs chronic.

1. Electrodiagnosis
Ncv/ Emg
Henry
Prakash
CMC
Vellore

2.  Assessment of sensory and motor function, integrity of PN &
muscle
 Always an extension of the what ever happens before that!
 Normal, Radiculopathy, Plexopathy, Neuropathy, Myo, AHC,
NMJ – eg to give
 Rules out other diseases

3.  Acute vs Chronic
 Localisation
 Symmetry
 Severity

4. Motor studies
 Myelinated large fibres
 Supramaximal response/
stimulus

5. Physiological temporal dispersion CMAPs & SNAPs
 CMAP
 SNAP

6. Phase cancellation between fast and slow
fibers
CMAPs SNAPs
 Demyelination differentially affecting fascicles of motor nerves
 Desynchronization of the CMAP
 CMAP amplitude is decreased, the duration is prolonged,
jagged configuration

7. Conduction block & Focal slowing

8. Sensory studies
 Only large myelinated nerve
fiber assessed
 Peak latency preferred
 Microvolts
 Wider range of CV among
the fibers measured
 Difference between fastest
and slowest fiber is about
25m/s
 More susceptible for phase
cancellation

9. Pre Post Ganglionic lesion and SNAP
 Sensory arrangment
 Antidromic /Orhtodromic pic

10. Antidromic Vs
Orthodromic

11. Late responses F & M
 F waves (so called first done
in foot)
 Wider sweep speed
 Retrograde supramaximal,
Motor impulse Diagram
 Info about proximal segment
 Limited sensitivity and
specificity
 Why 10 or more stimuli
 Shortest latency /Average

12. H
 Follows stretch reflex arc
 Afferent –Sensory 1alpha
 Efferent AMN
 Useful for S1 radiculopathy
 H/M ratio for UMN
assessment

13. Distal Amplitude
Distal Latency
Distal response dispersed
Distal Latency Demyelination /Axonal
Axon
al
Demyelination
Proximal Amplitude
> 50%
Slow Conduction
Velocity
Demyelinating
y Y
Y
Y
Y

14. Demyelination
 Prolonged DL
 Distal Amplitudes preserved but proximal reduced
 In severe demyelination amplitudes will be small

15. Physiological temporal dispersion CMAPs & SNAPs
 CMAP
 SNAP

16. Phase cancellation between fast and slow
fibers
CMAPs SNAPs
 Demyelination differentially affecting fascicles of motor nerves
 Desynchronization of the CMAP
 CMAP amplitude is decreased, the duration is prolonged,
jagged configuration

17. Autoimmune demyelination and TD

18. Conduction block & Focal slowing

19. Conduction block in demyelination
Simulates Axonal lesion

20. Anomalous innervations

21. EMG
 Needles
 Number of muscles and which depends on the questions to be
answered
 At rest and graded contraction
 Morphology and characteristics of wave

22. Fig. 1
Neurologic Clinics 2012 30, 429-456DOI: (10.1016/j.ncl.2011.12.009)
Copyright © 2012 Els
Neurologic Clinics Volume 30, Issue 2, Pages 429-456 (May 2012)

23. At rest – Spontaneous activity
 Insertional activity
 Endplate spike
 Fibs
 Psw
 CRD
 Myokymia
 Myotonia

24. Insertional activity
 Mechanical depolarisation of a single muscle fibre
 Length dependant on the number of muscle fibre
 Early sign of Neuropathy (2-3weeks)
 Variants possible in musclular young individuals
 Mutation of CLCN1 gene (Myotonia Cong.)

25. End Plate Activity
 MEPP – At the end plate , Random spont release of Ach
 Monophasic, Low amp (<10µv), Short duration (1-3ms)

26. Fibrillations
 Spontaneous in absence of innervation
 Regular pattern 0.5-15Hz
 Spike or Psw
 Amplitude depends on dia. of muscle fibre thus
 Better heard -Slow regular firing pattern
 Also occurs in sectioned and split muscles fibres – Lower amp
and slow rate (0.5Hz)
 Density a rough estimate of No. of denervated muscle fibres.1+
to 4+

27. CRD
 Arises from single muscle fibre AP
 Ephaptical spread
 Regular repetitive abrupt start and cessation
 3 – 40 Hz

28. Myokymic discharge
 Spontaneous MUAP firing
 Repetitive in burst fashion
 Each Burst has 1 or more MUAP, MUAPs may fire many times
within the burst
 40 – 60 Hz
 Regular ,Semi-rhythmic pattern interval- 0.1 to 10 sec
 Firing pattern not affected by voluntary contraction
 Marching

29.  Synkinesis – Facial synkinesis, Breathing Arm/Hand
 Hemifacial spasm - demyelination of the proximal facial nerve
or remodeling of the facial nerve nucleus within the brainstem.
As a result, spontaneously generated action potentials are
initiated in the facial nerve and ephaptically spread to adjacent
axons.

30. RNS
 Low frequency stim 3hz
 Draw Normal
 Myasthenia
 Draw
 Ach runs out amplitude decreases –Decrement 10-20%
after train 10 some recover – Due to Ca influx and Ach recycling

31. MUAP’s
 Configuration
 Amplitude, Duration. Morphology
 Normal,
 Neuropathic - High amplitude, Long duration , Polyphasic
 Myopathic – low amp, Short duration, Polyphasic
 Pattern
 Normal hinemans principle
 Reduced recruitment – Large MUAP Higher firing rate Incomplete
interference pattern
 Increased and early - Myopathic

32. MUAP
 Number of motor units within the muscle
 Number and diameter of muscle fibers,
 Arrangement and density of the fibers within the motor unit
 Synchrony of firing of each of the muscle fibers
 MUPs are recognized by the distinct semirhythmic pattern of
firing

34.  Technical factors - Type of needle electrode, Filter settings,
Proximity of needle to muscle fibres being recorded.
 Physiologic variables - Age, Muscle, Temperature, Strength of
activation.
 Innervation ratio (number of muscle fibers in the motor unit)
 Fibers density (number of muscle fibers per given cross-
sectional area)

35. Recruitment
 Relationship of the number of MUPs activated and the firing
rates at time relative to force of muscle contraction
 Single or a few MUPs begin to fire at rates of approximately 5
to 8 Hz.
 Increasing force - the firing rates steadily increase up to 20 to
40 Hz while, at the same time, the threshold of firing of
additional motor units is reached and additional MUPs are
“recruited.”

36.  Recruitment frequency is measured as the rate of firing of an
initially activated MUP when a second MUP is recruited
 A normal recruitment frequency for the second MUP is between
7 and 10 Hz in most limb muscles
 recruitment ratio - Rate of firing of an individual MUP to the
number of MUPs that are active
 Limbs – Ratio 5 or less
Neurologic Clinics Volume 30, Issue 2, Pages 429-456 (May 2012)

37. Reduced Recruitment
 Recruitment frequency and the recruitment ratio increase as
MUPs fire more rapidly before additional MUPs are recruited .

38. Duration Amplitude Phases Stability
 8-12 ms
 Level of activation
 Early Reinnervation - MUAPs small and short,
Frequently polyphasic, satellite
potentials
Interference pattern is severely
reduced
 Chronic Reinnervation - MUAPs large longer duration
Increased, amplitude, and number of
phases
Reduced interference pattern

39. Polyphasic MUPs (≥5 phases)
 Collateral sprouting, reinnervation, and an increase in fiber
density
Neurologic Clinics Volume 30, Issue 2

40. SFEMG
 MUPs fire repetitively under voluntary control normally have the
same amplitude, duration, and configuration each time they
fire.
 Fluctuation, varying or unstable MUPs - indicative of
dysfunction of neuromuscular transmission MUP stability can
be quantified with SFEMG.
 Moment-to-moment variation of MUPs is caused by blocking of
the discharge of action potentials of one or a few of the
individual muscle fibers composing the motor unit.
 Irritability /Variability between fibres within motor unit.
 Jitter

41. Raster mode
Neurologic Clinics Volume 30, Issue 2, Pages 429-456 (May 2012)

42. Thank You