Describes about Motor Nerve conduction studies, Sensory nerve conduction studies, F waves and H reflex

1. “Fundamentals Of Nerve Conduction
Studies And Its Interpretations”

2. Dr. T. Sureshkumar, MPT (Neuro), PhD
Principal,
Shree Siddheshwar College of Physiotherapy,
Solapur, (Maharashtra)

3. What is NCS?????

4. Nerve Conduction Study (NCS)
NCS is a test commonly used to
evaluate the function of the motor
and sensory nerves of the human
body

5. Uses
• Nerve conduction studies are used mainly for evaluation of paresthesias (numbness,
tingling, burning) and/or weakness of the arms and legs.
• Differentiation and Localization: ?? Nerve – muscle- NMJ
• Classify peripheral nerve conduction abnormalities due to axonal degeneration,
demyelination, and conduction block
• Differentiation between local or diffuse disease process (mononeuropathy or
polyneuropathy).
• Get prognostic information on the type and extent of nerve injury.

6. Common Disorders Diagnosed By NCS
• Peripheral neuropathy
• Mononeuropathy (ex: carpal tunnel syndrome)
• Mononeuritis multiplex (ex: leprosy,) •
• Polyneuropathy (ex: diabetic neuropathy,)
• Myopathy
• Muscular dystrophies (ex: Facioscapulohumeral muscular dystrophy)
• Radiculopathy
• Diseases of neuromuscular junction ( Myasthenia gravis)

7. Principles
• Peripheral nerves are stimulated with an controlled electrical stimulus
• Responses recorded
1. Compound Motor Action Potential (CMAP)
2. Sensory Nerve Action Potential (SNAP)
3. F wave
4. H- reflex

8. Electrodes
Recording (MNCS) Recording (SncS)

9. Electrodes
Ground Stimulator

10. Procedure
• Active recording electrode placed on the center of the muscle belly (over the motor
endplate)
• Reference electrode placed distally about 3-4 cm from active electrode.
• Ground electrode placed in between active and recording electrode
• Stimulator placed over the nerve that supplies the muscle, cathode closest to the
recording electrode.
• Current needed
• 1. 20-50 mA for motor NCS
• 2. 5-30 mA for sensory NCS
• Supramaximal stimulation is given.

11. Placement of electrodes (Ulnar nerve)

12. Some Basic terminologies…

13. Motor Nerve Conduction Velocity
• CMAP- it is summation of all underlying individual muscle
fibre Action potential
• biphasic potential with an initial negativity (upward
deflection).
• For each stimulation site: latency, amplitude, duration, and
area of the CMAP are measured.
• A motor conduction velocity can be calculated after two sites
of stimulation, one distal and one proximal.

14. Latency
• It is the time from the stimulus to the initial negative
deflection from baseline made in milliseconds (ms).
• Represents the largest conducting fibers
• Nerve conduction time from stimulus site to nmj
• Time delay across nmj
• Depolarization time across muscle

15. Amplitude
• Most commonly measured from baseline to the negative
peak (baseline-to-peak)
• Reflects the number of muscle fibers that depolarize.
• Low CMAP amplitudes most often result from
• Loss of axons (as in a typical axonal neuropathy),
• Demyelination with conduction block,
• Presynaptic NMJ disorder,
• Advanced myopathy

16. Area
• CMAP area is measured between the baseline and the
negative peak.
• Is determined by no. of fibers that depolarize
• Reduced in Conduction block from demyelination

17. Duration
• Measured from the initial deflection from baseline to
the final return
• Increased in demyelinating disorders

18. Conduction Velocity
• measure of the speed of the fast conducting motor axons
• Calculated by dividing the change in distance (between proximal stimulation site & distal
stimulation site in mm) by the change in time (proximal latency in ms minus distal latency in
ms)
• Reduced in demyelination due to increased electrical resistance from damaged myelin
• Normal values are
• > 50 meters/sec in the upper limbs And
• > 40 meters/sec in the lower limbs

19. Normal Values
NERVES Latency (ms) Amplitude (mA) Velocity (m/s)
Median <4.2 >5 >48
Ulnar <4 >5 >48
Radial <2.9 >2 >49
Peroneal <6 >5 >49
Tibial <6 >5 >49
Musculcutaneous <5.7 >2 >48
Axillary <4.9 >2 >48

21. Sensory Nerve Conduction Studies
• This NCS represents the conduction of an impulse along the
sensory nerve fibers.
• It is performed by electrical stimulation of a peripheral nerve
and recording from a purely sensory portion of the nerve, such
as on a finger.
• The recording electrode is placed proximal to the stimulating
electrode. (antidromic nerve impulse is recorded)
• The sensory NCV is calculated based upon the latency and the
distance between the stimulating and recording electrode

22. Sncs-ulnar Nerve

23. Orthodromic Method
• Stimulating electrode over distal
sensory branches of nerve
• Recording electrode over more
proximal point on nerve trunk.
• The nerve will conduct the impulse
orthodromically as normal from distal
to proximal.

24. Antidromic method
• Stimulating electrode over proximal point on
nerve trunk.
• Recording electrode at distal sensory
branches of nerve
• Nerve will conduct impulse antidromically
from proximal to distal

25. Sensory Nerve Action Potential
SNAP: summation of all individual sensory nerve fiber
action potentials
Onset Latency: is the time from the stimulus to the first
deflection from baseline
represents nerve conduction time for the largest
cutaneous sensory fibers
used to calculate conduction velocity
Peak Latency: is measured at the midpoint of the first
negative peak
Increases in demyelination

26. Normal values (sNCS)
Nerves Latency (ms) Amplitude (uv) Velocity (m/s)
Median <3.4 >15 >48
Ulnar <3.4 >15 >48
Sup.Radial <2.9 >15 >48
Sural <3.4 >5 >42
Sapheneous <3.9 >2 >40

27. Late response
• When a nerve stimulus applied it travels in to 2
direction,
• peripheral stimulation (orthodromic) result in M-
response
• while towards anterior horn cell stimulation(antidromic)
• result in to late response.
• In routine only one late response is measured i.e.F
response.

28. F Response
• The nerve is stimulated supramaximally distally with
the cathode placed proximally to avoid the theoretic
possibility of anodal block
• Recording second MP after20-40ms delay F wave has
variable latency with repetitive stimulation
• Uses:
• Early GBS
• C8-T1, LS-S1 radiculopathy
• Polyneuropathy
• Internal control (entrapment neuropathy)

29. • Conduction velocity is derived by measuring the limb length
in millimeters from the stimulation site to the
corresponding spinal segment (ex: C7 spinous process to
wrist crease for median nerve).
• This is multiplied by 2 as it goes to the cord and returns to
the muscle.
• The difference between both sides’ shortest latencies
should not exceed l ms.

31. F- Ratio
• The F-ratio is then obtained by dividing the proximal latency by the distal latency:
• With normal routine conduction velocity:
– A decreased F-ratio indicates a distal nerve lesion or entrapment (such as carpal
tunnel)
– An increased F-ratio indicates proximal slowing
• With slowed routine conduction velocity:
– A normal F-ratio indicates equal proximal and distal slowing
– A decreased F-ratio indicates a normal proximal segment
– An increased F-ratio indicates a predominant involvement of the proximal nerve
segment

32. H Reflex
• This NCS creates a late response that is an electrically evoked analogue
to a monosynaptic reflex.
• It is initiated with a submaximal stimulus at a long duration (0.5–1.0
milliseconds).
• This preferentially activates the IA afferent nerve fibers, causing an
orthodromic sensory response to the spinal cord, and then an
orthodromic motor response back to the recording electrode.

34. • The H reflex provides a measure of nerve conduction along
the entire length of the tibial/S1 pathway, providing
information along proximal nerve segments, including the
plexus and roots
• Diagnosis of S1 and C7 root lesions as well as the study of
proximal nerve segments in either peripheral or proximal
neuropathies.
• Active placed over the distal to soleus, reference at achilles
tendon and ground between recording and stimulating
electrode
• Stimulated at popliteal fossa
• Its absence or abnormal latency on one side strongly
indicates disease

36. Interpretation
• The speed of nerve conduction is related to – the diameter of the nerve and, – the degree of
myelination
• A normally functioning nerve will transmit a stronger and faster signal than a damaged
nerve.
• in general, different pathological processes result in: – changes in the latencies – changes in
the amplitudes – slowing of the conduction velocity

37. • Examples; – slowing of the NCS usually indicates there is damage to myelin.
• – slowing across the wrist for the motor and sensory latencies of the median nerve indicates focal
compression of the median nerve at the wrist, called carpal tunnel syndrome.
• – slowing of all nerve conductions in more than one limb indicates generalized peripheral
neuropathy (eg. in diabetes mellitus).

38. Disorder Latency Velocity Amplitude Duration
axonal Normal or
prolonged
Decreased or
absent
Decreased Normal or
prolonged
Demyelinating Prolonged Decreased Normal or reduced
if conduction block
Prolonged
NMJ disorder Normal Normal Normal or reduced Normal
Myopathic Normal Normal Normal or reduced Normal

39. Thank you