1. Introduction to electrodiagnostic testing (EMG/NCS)
Calin I. Prodan, MD
Department of Neurology
University of Oklahoma Health Sciences Center

2. Electrodiagnostic testing in Neurology
Components:
Nerve conduction studies (NCS)
Needle electromyography (EMG)
Other components:
Repetitive stimulation
Single-fiber EMG
Intraoperative monitoring

3. NCS Sensory nerves: Motor nerves
Amplitude
Velocity (distance divided by time)
Motor nerves
Velocity
F-wave response
Uses a gradually increased amount of electrical stimulation in order to obtain an motor/sensory response

4. Nerve Conduction Studies
Amplitude of the response
Amplitude (mV)
Time (ms)

8. Sensory Pathways Receptor organs (sensory transducers)
Peripheral nervous system pathway
Spinal (ascending) pathway
Thalamic “relay”
Cortical representation

9. Pain & Temperature Pathway “Spinothalamic system”
Receptors are naked nerve endings
Peripheral unmyelinated (C) and small-myelinated (A) fibers
Ascending spinal cord pathway
Carried to the thalamus
The speed of conduction for pain and temperature sensation is very slow

10. Proprioception Pathway
Receptors are specialized organelles including muscle spindles, Golgi tendon organs, and Pacinian corpuscles
Peripheral large-myelinated (A and A) fibers
Ascending spinal cord pathway
Carried to the thalamus
The speed of conduction is fast

11. Spinothalamic vs Proprioception Pathways
Pain & temperature
Naked nerve endings
A and C fibers (slow)
PROPRIOCEPTION
Proprioception
Specialized receptor organelles
A and A fibers (fast)

12. Electrodiagnostic studies: Nerve Conduction Studies
NCS will only study large-myelinated nerve fibers, distal to the DRG.
Hence, they are normal in myelopathy, radiculopathy and small-fiber
neuropathy, despite clinically evident sensory loss.

13. EMG Insertion of a needle electrode in various muscles
Recording muscle activity at rest and during activity (volitional activity)
Requires a lot of cooperation and cannot be performed accurately in patients with severe weakness

14. EMG
Fibrillation
Fasciculations
Normal voluntary activity

15. EMG/NCS Indications: Polyneuropathy
Entrapment neuropathy (carpal tunnel, etc.)
Myasthenia gravis
ALS
Radiculopathy
Myopathy/Myositis
Plexopathy
Any combination of the above

16. EMG/NCS Elective procedure
Extension of clinical diagnosis – NOT to make a dx
Grade severity (mild, moderate, severe) i.e. define the need for surgical intervention
Prognosis (myasthenia, ALS, GBS)

17. When to refer for EMG/NCS
Radiculopathy:
Part of surgical evaluation for cervical and LS spine surgeries
Very low yield in pure sensory c/o or pain
Higher yield with weakness and reflex changes
Prior to repeating a surgery
Post-surgical complications (from the surgical service)

18. Radiculopathies
“Numbness” and pain in the appropriate dermatomal distribution.
Often associated with focal myotomal weakness, focal hyporeflexia and back pain.

19. Radiculopathy– Electrodiagnostic studies
Nerve conduction studies:
normal
EMG:
denervation changes (fibrillation potentials and fasciculations) within muscles innervated by the root involved and paraspinal muscles adjacent to the root
other muscles in the same extremity and any other muscles are normal

20. When not to refer for EMG/NCS
Radiculopathy:
Low back/neck pain with or w/o radicular pattern – patients should be treated medically and imaged (X-ray)
Low back/neck pain with sensory c/o or sensory findings -patients should be 1st treated medically and imaged (X-ray)
anticoagulation (cannot perform complete EMG)
Patient states that he does not want surgery or not a surgical candidate

21. When to refer for EMG/NCS
Polyneuropathy:
Consider risk factors (including DM and ETOH)
Not an early test
Serology and symptomatic treatment should come first
When considering biopsy

22. Peripheral Nerve Disease (Neuropathy)
Small-Fiber Neuropathy
Large-Fiber Neuropathy

23. Spinothalamic vs Proprioception Pathways
Pain & temperature
Naked nerve endings
A and C fibers (slow)
PROPRIOCEPTION
Proprioception
Specialized receptor organelles
A and A fibers (fast)

25. Length-dependent (dying back) axonal neuropathy

26. Small-Fiber Neuropathy

27. Small-Fiber Neuropathy– Electrodiagnostic studies
COMPLETELY NORMAL

28. Large-Fiber Neuropathy
History:
Constant unsteadiness
Frequent falls
slow (months/years) progression
No numbness, tingling, pain
first involves feet/legs then hands/arms

29. Large-Fiber Neuropathy
Examination:
Decreased proprioception (joint position) and vibratory sense (tuning fork) in a “stocking and glove” distribution
Normal OR decreased temperature/pain sensation in a “stocking and glove” distribution
Reflexes are decreased (legs > arms)
Gait is very unsteady (wide-based)
Weakness in feet > hands is a late sign

30. Large-Fiber Neuropathy– Electrodiagnostic studies
Nerve conduction studies:
decreased amplitude or absent responses
changes are greater in the lower extremities than upper extremities
EMG:
normal
in longstanding disease it may show denervation in distal muscles

31. Electrodiagnostic studies
Nerve conduction studies (NCS)
the most important non-serologic test for the diagnosis of neuropathy
Electromyography (EMG)
helps evaluating the effect on muscles
rules out muscle disease

32. Segmental Demyelination
Schaumburg, Berger & Thomas, 1992

33. Demyelinating Polyneuropathies
Segmental demyelination is a random process:
Statistically more likely to affect longer nerves (i.e. legs) first and most severely.
But any nerve segment can be affected, so proximal and facial weakness can occur early.
Disruption of large-fiber nerve function: early weakness, areflexia and sensory ataxia.
Schaumburg, Berger & Thomas, 1992

34. Features of Acquired (Segmental) Demyelination:
(1) Partial motor conduction block (PMCB)
(2) Temporal dispersion (TD)
(3) Asymmetric conduction slowing between nerves and in proximal/distal segments of the same nerves

35. Acquired Demyelinating Polyneuropathies Segmental Demyelination
Usually immune mediated
ACUTE (nadir within 4 weeks)
Guillian-Barré Syndrome
Treat with IvIgG or PE
CHRONIC (progress slowly for > 6 weeks)
CIDP
Treat with corticosteroids, IvIgG or PE

36. When to refer for EMG/NCS
Entrapment neuropathy:
Part of surgical evaluation (NES, Ortho, plastics)
Part of initial evaluation if sensory/motor changes are present
After at least 6-8 weeks of smx
When not to refer for EMG/NCS:
if only sensory c/o (treat – splints, pads, NSAIds, pain management)
patient refuses surgery

37. Focal Neuropathies in the Upper Limb Carpal Tunnel Syndrome (CTS)

38. Carpal Tunnel Syndrome (CTS)
Commonest focal neuropathy encountered
Entrapment of the median nerve beneath the flexor retinaculum at the wrist
Symptoms:
numbness and pain the wrist and hand
worse at night and with repetitive motions
relieved by shaking
Signs:
numbness in median nerve distribution
weakness/wasting of APB, sparing FDI/ADM
Tinel’s and Phalen’s signs

39. Carpal tunnel syndrome
Diagnosis:
clinical
NCS (80-90% even in mild cases)
Labs:
always screen for diabetes and thyroid disease
NCS:
Slow conduction velocity (sensory/motor) across the wrist
+/- decreased amplitude
+/- prolonged F-wave
EMG
+/- denervation (acute and/or chronic)

40. Carpal tunnel syndrome
Treatment:
wrist splints
NSAIDs
treat the predisposing condition
Surgical release:
surgical release (90% success rate)
Indicated mostly in moderate and severe cases
Outpatient surgery (plastics, ortho, NES, GS)

41. When to refer for EMG/NCS
Myopathy/myositis:
Not an early test
Serology (including myositis antibodies) and treatment should come first
When considering biopsy

42. Myopathy
Werwerwr

43. Myopathy/Myositis– Electrodiagnostic studies
Nerve conduction studies are normal (motor and sensory nerves)
EMG - pathy:
No denervation (spontaneous activity at rest)
Small units when symptomatic muscles are activated even with maximal effort
EMG – itis:
Denervation

44. When to refer for EMG/NCS
ALS, MG, plexopathy:
Not an early test
Serology/treatment/imaging should come first

45. MND

46. MND

47. MND– Electrodiagnostic studies
Nerve conduction studies:
sensory nerves are normal
motor nerves +/- low amplitude response
conduction velocities are normal
EMG:
the crucial test for diagnosis
widespread denervation changes (spontaneous activities at rest) – fibrillation potentials and fasciculations in all extremities/thorax and even face/tongue

48. Muscular dystrophy Family history of similar issues
Most often EMG/NCS NOT indicated
DNA testing available
= Myopathy with positive FH

50. Neuromuscular Junction Disease
Post-synaptic NMJ
Myasthenia Gravis (MG)
Pre-synaptic NMJ
Eaton-Lambert syndrome (ELMS)

51. MG History: Hallmark is fluctuating fatigable weakness.
double vision (diplopia) and droopy eyelids – very common (60-70)
difficulty swallowing, chewing and talking – common (15-20%
limb weakness – less common (10%)
weakness fluctuates during the day
strength normal in the AM, weakness most pronounced in PM
weakness is triggered by repetitive activities
strength improves with rest
severe cases may lead to respiratory failure and death
Hallmark is fluctuating fatigable weakness.

52. MG – Electrodiagnostic studies
Nerve conduction studies are normal (motor and sensory nerves)
EMG is normal
Repetitive stimulation (2-3 Hz) of a distal motor nerve may produce a decrease in the amplitude of the motor response ( > 10%)

53. MG – Repetitive stimulation

54. ELMS History: Heaviness/fatigue in the upper portion of the limbs
Trouble going up/down stairs or getting in/out a chair
NO double vision/droopy eyelids/difficulty swallowing, chewing or talking
Hallmark is improvement with exercise

55. ELMS – Electrodiagnostic studies
Nerve conduction studies are normal (motor and sensory nerves)
EMG is normal
Repetitive motor stimulation at 2-3 Hz may produce a decrease in the amplitude of the motor response (5- 20%)
Repetitive motor stimulation at Hz will produce an increase in the amplitude of the motor response ( %)

56. ELMS – Repetitive stimulation

57. ELMS – Repetitive stimulation

58. EMG/NCS Involves significant discomfort Relatively expensive ( = MRI)
Requires patient cooperation
Takes approx. 1 hour

59. Carpal tunnel screen (CTS)
Carpal tunnel screen clinic – EMG lab
Screening test: both median nerves across the wrists and both ulnar nerves at the wrist (motor and sensory component)
No needle testing
Can be done on a same-day basis