This PPT describe in detail graphical representation of EMG, NCV and H- Reflex

1. Electromyography (EMG) and Nerve
Conduction Studies (NCS)
Dr. Preeti Ghodge (M.P.T)

2. Electromyography (EMG) and Nerve
Conduction Studies (NCS)

3. Electro-diagnostic testing
Components - examination of nerves and muscles:
 Needle electromyography (EMG)
 Nerve conduction studies (NCS)

4. Indications
Suspected neuromuscular disease:
• Nerve root pathology
• Peripheral nerve/plexus pathology
• Neuromuscular junction pathology
• Muscle pathology

5. EMG/NCS Diagnose
• Neuromuscular Diseases
• It can differentiate:
Normal
Radiculopathy
Plexopathy
Neuropathy(focal , peripheral/poly)
Myopathy
Widespread denervation(MND)
Disorder of neuromuscular transmission(MG)
• It can rule out other diagnoses

6. Value
• Time course of disease
Acute vs. chronic vs. acute & chronic
• Anatomical location of pathology
Root
Plexus
Nerve(axonal,demyelinating)
Neuromuscular junction
Muscle
Specific sites
• Distribution
Polyradiculopathy
Trunk, Cord
Mono vs. Multiplex vs. distal symmetric
• Severity of disease

7. Limitations :
• Generally not helpful in evaluation/diagnosis of:
 Pain from joint disease
 Fibromyalgia or myofascial pain syndromes
 Central nervous system disorders
 Disorders that do not arise from the neuromuscular system

8. Electromyography
• Recording and analyzing the action potential of a muscle.

9. Electromyography Prerequisites
 Prior clinical examination
 Rough plan of test
 CPK levels
 Hemophilia & bleeding disorders
 Large muscles

10. Needle Electromyography
• Needle electrode is inserted into muscle
Needle is disposable, single use
Concentric (both recording and reference in same
electrode)
• Multiple muscles are accessible for examination
• Combination of muscles tested
Dependent upon clinical question
• Level of discomfort is mild

11. Needle Electromyography: Data
• Insertional Activity
• Spontaneous Activity
• Interference Pattern

12. EMG:
Spontaneous Activity
10 msec/div, timebase
2MV/vertical segment
Positive Sharp Waves Fasciculation Potential
Fibrillation Potential
Neurogenic Motor Unit Motor Unit Changes

13. EMG data

14. Muscle is studied at rest & at different levels of
sustained, voluntary contraction
• At rest , the muscle should be silent –any spontaneous activity
may signal a nerve abnormality
• During activity, the electrical shape and pattern of the response
can distinguish between nerve and muscle disease

15. Parameters evaluated
• Motor Unit Configuration :
Muscle is volitionally activated at different force levels
Single motor units are assessed (motor unit action potential
or MUAP-reflecting activity of all muscle fibers innervated by
single motor axon)
Assess amplitude,duration,morphology
Essentially three patterns:
Normal
Neuropathic (high amplitude,long duration,polyphasic)
Myopathic (low amplitude,short duration,polyphasic

16. Motor Unit Recruitment and interference pattern:
• Normal: graded recruitment of initially small then larger
MUAPs, full interference pattern
• Reduced Recruitment: large MUAPs at high firing rates,
incomplete interference pattern .seen with neuropathic
conditions
• Increased (early) Recruitment .Seen in myopathy
• Dependent on patients co-operation and effort

17. Components of an Electro-diagnostic Machine

18. Gain – Sweep representation
Duration (ms) x axis
Latency
(mV)
y
axis
Gain = Latency
Sweep = Duration

19. Nerve Conduction Studies
• Peripheral nerves stimulated with controlled electrical stimulus
(supra-maximal)
Generally useful for distal/extremity nerve only e.g.
median/ulnar/radial in UL, tibial/peroneal/sural in LL
More proximal nerves can be tested in specific situations
• Current depolarises nerve membrane & initiates action potential in
axon
When all possible axons in nerve depolarised,get “supra-
maximal” response
• Action potential travels along nerve
Speed on conduction depends on integrity of “insulating”
myelin membrane to allow saltatory conduction
Conduction along non-myelinated fibers much slower

21. Motor nerve

22. Propogation of action potential

23. Nerve Conduction Studies
• Responses are recorded
Motor studies: Compound motor action Potential (CMAP)
Sensory studies: Sensory nerve action potential(SNAP)
F-wave
H-reflex
• Assess large myelinated fibers only
not useful for small fiber disorders
• Assess for:
Axonal processes (axon loss, Wallerian degeneration)
Focal demylinating processes (slowing,conduction block)

24. Motor NCS Parameters
 Distal Motor Latency (DML)
• Time from stimulation to onset of muscle contraction
• Determined by conduction velocity of the nerve , neuromuscular
junction &muscle.
• Prolonged in demyelinating neuropathies, with compression
 Amplitude
• Determined by number of muscle fibers activated
• Varies with stimulus intensity ,impedance,skin temperature
• Reduced with axonal neuropathies, drop from distal to proximal
site (conduction block) in demyelinating
 Proximal conduction velocity (CV)
• Determined by conduction velocity of the fastest fibers
• Derived from ditance between distal & proximal site divided by
latency difference
• Marked reduced in demyelinating neuropathies

25. Normal Median Motor study

27. Worked motor study
• Initial stimulation of median nerve at
wrist
• Sub maximal stimulation gives small
CMAP
 Not all axons depolarised & so
not all motor units activated.

29. Worked motor study
 Supra-maximal stimulation gives
“best” amplitude CMAP possible
 Amplitude
• Marked of number of motor units
activated & thus how many axons
activated
• Reduction suggests axonal loss
 Distal latency
• Reflects time for action potential
to travel down segment of nerve
plus time for neuromuscular
transmission
• Any prolongation suggests
problem in this segment of nerve.

31. Worked motor study
• More proximal stimulation
• Look for:
• Any change in morphology
• Any drop in amplitude (“conduction
block”) which reflects demyelination or
other focal process affecting nerve across
the segment studied
• Can calculate conduction velocity from
distance (measured from active stimulus
point/cathode site in cm or mm) divided by
time (latency difference between the two
stimulus sites)

32. Worked motor study
• The report usually presents the relevant figures
Distal latency
Distal amplitude
Velocity across segments
Proximal latency (compared with distal)
Nerve / Sites Latency
ms
Amp
mV
Velocity
m/s
R MEDIAN -APB
Wrist 3.50 6.8
Elbow 7.30 6.2 59.2

33. Sensory nerve

34. Pre and post-ganglionic lesions

36. Sensory NCS Parameters
 Onset and Peak latencies
 Conduction velocity
• Determined by velocity of a very few fast fibers
 Amplitude
• Determined by the number of large (myelinated) sensory
fibers activated

37. Normal Median Sensory Study

39. Worked sensory study
• Generally only single stimulus site
• Can be recorded
orthodromically(same way as nerve
conduction) or antidromically
•Much smaller than motor
responses(micro vs. millivolts) & so
more prone to artifact

41. Worked sensory study
• Record
-Amplitude(again marker of number of axons)
-Latency
-Conduction velocity

42. Late Responses
• F-Wave Latency
Retrograde “rebound” motor impulse, travels full length of
motor axon and back
Information about proximal nerve segments
Limited sensitivity/specificity
Helpful in the evaluation of radiculopathy, GBS, other
demyelinating neuropathies, peripheral neuropathy

43. H-Reflex
• Follows muscle stretch reflex arc
Afferent path= sensory Ia fibers
Efferent path= alpha motor neurons
• Side to side latency most valuable
• Helpful in the evaluation of polyneuropathy,S1 radiculopathy,
upper motor neuron lesions

44. F Waves: Normal Median

45. Algorithm for each nerve

46. Putting it together

47. Value of NCS
• Define & localise focal neuropathies
Especially carpal tunnel syndrome, ulnar neuropathies,wrist
and foot drop
• Define severity & pathophysiology of peripheral neuropathies
Axonal
Demyelinating

48. Summary
• Confirms provisional diagnosis
• Efficacy of intervention
• Study the prognosis of the disease

49. • Electro-physiological Studies enhances the
Diagnostic Value and Prognostic ability

50. THANK YOU..