1. Clinical neurophysiology exploration (cne01)
Professor Dr. Magd Fouad Zakria
Head of Neurology department, Faculty of Medicine
Ain-Shams University, Cairo-EGYPT
Instructor: Prof. Dr. Amal Fouad
Professor of Neurology,
Neurology department, Faculty of Medicine

2. Elementary nc and emg Professor Amal Fouad Professor of Neurology
Seminar 1
Elementary nc and emg
Professor Amal Fouad
Professor of Neurology
Faculty of Medicine
Ain-Shams University
Cairo-EGYPT

3. Motor Nerve Conduction Study
Sensory Nerve Conduction Study
Neuromuscular Transmission and Myasthenic Syndrome
EMG (detection type) in Neuropathies and Myopahties
Resting EMG activities
Muscular excitability, Myotonic syndromes and periodic paralysis

4. Motor nerve conduction study

5. Motor Nerve Conduction Study
Searching for a neurological substrate explain the clinical signs
Complementary to clinical examination that allows to the differentiation of clinically similar pathology
Search for electrophysiological signs that can confirm or exclude an initial clinical diagnosis
Operator dependant: (why it might change from operator to operator, technique used, possibility to create abnormalities which do not exist)
Making this exam less painful and even painless
Why?

6. Motor Nerve Conduction Study
Electric stimulation of a target nerve on diverse points along its pathway (detection of possible pathology and its localization
Analysis of the electric response obtained by stimulation of a innervated muscle located in the territory of the examined nerve
Appreciation of the nature and severity of the nerve dysfunction
Principals:

7. Absence of abnormalities in motor nerve conduction study does not eliminate the possibility to have a chronic neurogenic denervation with collateral reinnervation which could be only detected by needle study (more sensitive that surface EMG)

8. Principals of motor nerve conduction study

9. Figure 1: placing surface electrodes for studying the distal motor latency (median nerve at wrist, receiving the electric response on abductor pollicis brevis
Séminologie ENG élémentaire: Technique d’étude de la conduction nerveuse motrice. Prof. Emmanuel Fournier 2008

10. Stimulation: Activation: Recording: Technique
Rectangular current with a short duration 0.3ms and variable intensity (5-25mA)
Activation:
Each stimulated nerve fibre generate an action potential which then conducted separately via the corresponding nerve fibre
Recording:
Nerve action potential is the sum of the of all separate nerve fibre action potentials
Stimulation
Activation of nerve fibres
recording

11. Stimulation
CMAP
Nerve
Summation
Figure 2: Motor response of motor nerve

12. Motor Nerve Conduction Study: Technique

13. Technique Description precautions
Physiological bases
Parameters measured
Normal values
The main abnormalities
precautions
During stimulation
While receiving the recorded response
Measuring the distance between two stimulated points
Pathological and technical causes of abnormalities

14. Technical description: physiological bases

15. Supramaximal stimulation. WHY?
Recording the muscular response which is the potential difference between the active and the reference electrodes. Where we place active and reference electrodes?
Supramaximal stimulation: supramaximale pour pouvoir évaluer le nombre de fibres nerveuses fonctionnelles
active sur le muscle • référence sur le tendon • réponse motrice = PAMC = potentiel d’action musculaire composé : somme des pot d’action musculaires provoqués par la stimulation nerveuse (compund muscle action potential CMAP)

16. Start and phases
Positive wave representing repolarization and the action potentials getting far from the active electrode)
Start of negative wave (initial action potentials of muscle fibres under the active electrodes)
Valable pour le potentiel d’action d’une fibre musculaire.
Plus complexe à interpréter pour un muscle (nombreuses fibres, désynchronisation : voir plus loin)

17. Technical description: Parameters measured

18. Parameters measured Proximal stimulation site for median nerve: S2, A2
Distal Latency : DL
Motor Conduction Velocity: MCV
Distal stimulation amplitude :A1
Proximal Stimulation amplitude: A2
Distal stimulation site for median nerve, S1, A1
Distance in mm

19. Distal amplitude A1 (normal: 6-10 mV) Reduction: Axonal degeneration
Distal Latency: (normal 3-4 ms)
Augmentation: distal demyelination
Amplitude A2/A1(normal: %)
Reduction: Conduction block
dt ms
MCV= d/dt (normal: m/s
Reduction: segment demyelination
Amplitudes des réponses
–  détecter les pathologies induisant une réduction du nombre de fibres fonctionnelles dans le nerf (notamment par dégénérescence axonale)
–  Donc, en surface
–  Expliquer les faiblesses !!!
Figure 3: Parameters of motor nerve conduction of median nerve

20. Differential diagnosis

21. Figure 4: Motor nerve conduction of median nerve at different level
Seraching for the affected nerve segment by conduction block or reduction of nerve conduction
Appreciation of the severity of affection and axonal loss by the distal amplitude
Limitation: no possibilty for proximal segement study (root)
Séminologie ENG élémentaire: Technique d’étude de la conduction nerveuse motrice. Prof. Emmanuel Fournier 2008

22. Figure 5: Motor nerve conduction of ulnar nerve at different level
Figure 5: Motor nerve conduction of ulnar nerve at different level. Reduction of conduction velocity at segment 3(elbow level) and conduction block with diminution of A3
Definition of conduction block: functional lesion sufficient to suspend the function (nerve conduction) without nerve degeneration of its peripheral part
Séminologie ENG élémentaire: Technique d’étude de la conduction nerveuse motrice. Prof. Emmanuel Fournier 2008

23. Motor Nerve Conduction: Practical part

24. How to exam motor nerve conduction study for the following nerves:
Median nerve
Ulnar nerve
Peroneal nerve