Nerves conduction study

enjoy

1. Nerves conduction study Basic neurophysiology Dr Sachin Adukia

2. Elements of the peripheral nervous system.

3. Uses paraesthesias (numbness, tingling, burning) weakness of the arms and legs Differentiation and Localization: ?? Nerve – muscle- NMJ d/b local or diffuse disease process ( mononeuropathy or polyneuropathy) Classify peripheral nerve conduction abnormalities due to axonal degeneration, demyelination, and conduction block Early diagnosis eg . AIDP Extent of severity Get prognostic information on clinical course and treatment response

4. Disorders of the Peripheral Nervous System

5. Classification of nerve fibres

6. Limitations conduction velocity and latency measurements are from largest and fastest fibers . Large-diameter fibers have the most myelin and the least electrical resistance faster conduction velocities . NCS study only largest A-alpha fibers poses a problem where strength , & vibration and position senses are unaffected but pain and temperature sensations are abnormal: " small fiber neuropathy” Thus, neuropathies affecting small fibers may not reveal any abnormalities on N C Ss

7. The procedure Electrodes Skin will be cleaned electrodes will be attached to the skin along the nerves being studied Stimulus Small stimulus is applied (electric current) that activates the nerves ?? Discomforting but not painful Current Electrodes measure the current that travels along the nerve pathway

8. Procedure for motor study Active electrode placed on the center of the muscle belly (over the motor endplate) Reference electrode placed distally about 3-4 cm from active electrode (over tendon or bone ) Ground electrode in between active and recording electrode Stimulator / recording electrode is placed over the nerve that supplies the muscle, cathode closest to the recording electrode. Current needed (our lab) 15 -35 mA for motor NCS < 20 mA for sensory NCS Supramaximal stimulation is given in motor studies

9. Components of NCS Compound Motor Action Potential (CMAP ) Sensory Nerve Action Potential (SNAP ) F-wave study H-reflex study

10. CMAP Compound action potential- motor or sensory

11. Motor conduction study Belly-tendon montage Active recording electrode ( GI ) is placed on the center of the muscle belly (over the motor endplate), R eference electrode ( G2 ) is placed distally, over the tendon to the muscle Stimulator - placed over the nerve that supplies the muscle cathode placed closest to the recording electrode Ground electrode - In between stimulating and recording electrode

12. Upper limb- Motor

13. Lower limb- Motor

14. Technique As current is slowly increased by 5- 10 mA more nerve fibers are brought to action potential and subsequently more muscle fiber action potentials Threshold stimulus Maximal stimulus When CMAP no longer increases in size, can presume that all nerve fibers excited  supramaximal stimulation At our lab: 30% above maximal stimulation

15. Compound muscle action potential (CMAP) CMAP : summation of all underlying individual muscle fiber APs Biphasic potential with an initial negativity, or upward deflection from the baseline . Comprises of : Latency Amplitude Duration Area Stimulation

16. click Motor Latency Represents the largest conducting fibres nerve conduction time from stimulus site to NMJ time delay across NMJ depolarization time across muscle

17. click Amplitude of M wave Amplitude : commonly measured from baseline to the negative peak Represents no. of fibres that depolarize Causes of reduced amplitude (1) Axonal neuropathy (2) Demyelation with conduction block (3) Presynaptic NMJ disorder (4) Advanced myopathy

18. CMAP area : measured between the baseline and the negative peak Is determined by no. of fibres that depolarise Reduced in Conduction block from demyelination Distal area Proximal area

19. CMAP duration: measure of synchrony (extent to which individual muscle fibers fire simultaenously ). measured from the initial deflection from baseline to the first baseline crossing (i.e., negative peak duration) also measured from initial to terminal deflection back to baseline. increased in demyelinating disease.

20. Conduction velocity Measure of the speed of the fastest conducting motor axons. Conduction velocity (m/s) calculated as: distance between 2 stimulus sites (m) difference between 2 latency (s) Reduced in demyelination due to increased electrical resistance from damaged myelin

21. Motor nerve conduction: Latency on stimulation of peripheral n .- T1 same nerve stimulated at a more distal point, this latency is (T 2 ) Distance between 2 points of stimulation is measured in cm. click T 1 T 2

22. References values at our lab Motor ms mA m/s Latency Amplitude Velocity Median <4.2 >5 > 48 Ulnar <4 >5 > 48 Deep peroneal <6 >2 > 42 Posterior tibial <6 >5 > 42 Radial <2.9 >2 > 49 Musculocutaneous <5.7 Compare Axillary <4.9 Compare Suprascapular <3.7 Compare Femoral >3 Sensory uV Median <3.4 >15 > 48 Ulnar <3.4 >15 > 48 LABC <3 >15 > 50 MABC <3.2 >10 > 50 Superfical peroneal <3.4 >5 >42 Sural <3.4 >5 >42 Sapheneous <3.9 >2 > 40

23. Sensory nerve conduction E lectrodes (GI and G2) are placed in line over the nerve I nterelectrode distance : 2.5 to 4 cm A ctive electrode (GI) placed closest to the stimulator S = Stimulus point, T = Takeoff point, P = Peak Time ( latency) is from S to T measured in milliseconds . Amplitude = microvolts ( μV ).

24. Sensory nerve action potential (SNAP) 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 Inter examiner variation is less Used when onset latency is unclear Increases in demyelination

25. Onset latency vs Peak latency Peak latency Onset latency ???

26. Duration: measured from onset of potential to the first baseline crossing (i.e., negative peak duration ) The SNAP duration typically is much shorter than the CMAP duration (typically 1.5 ms vs 5-6 ms ) Amplitude: measured from baseline to negative peak Low SNAP amplitudes indicates axonal loss

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

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

29. Upper limb- Sensory

30. Lower limb- Sensory

31. References values at our lab Motor ms mA m/s Latency Amplitude Velocity Median <4.2 >5 > 48 Ulnar <4 >5 > 48 Deep peroneal <6 >2 > 42 Posterior tibial <6 >5 > 42 Radial <2.9 >2 > 49 Musculocutaneous <5.7 Compare Axillary <4.9 Compare Suprascapular <3.7 Compare Femoral >3 Sensory uV Median <3.4 >15 > 48 Ulnar <3.4 >15 > 48 Superfical peroneal <3.4 >5 > 42 Sural <3.4 >5 > 42 LABC <3 >15 > 50 MABC <3.2 >10 > 50 Superficial radial <2.9 >15 > 48 Sapheneous <3.9 >2 > 40

32. Limitation of Sensory conduction Lesions Proximal To DRG  Normal Sensory Potentials. Eg . Sensory Roots, Spinal Cord or Brain since Cell bodies are in DRG If pt. has Sensory Symptoms or Sensory LOSS with Normal Sensory Study consider a Proximal Lesion In case of Proximal MOTOR Root lesion or AHC Lesion  Degeneration of Motor Fibers throughout the Nerve – thus NCS is abnormal

33. DISORDER LATENCY VELOCITY AMPLITUDE DURATION AXONAL NORMAL (<130%) NORMAL (>75%) DECREASED NORMAL DEMYELINATING PROLONGED (>130%) DECREASED (<75%) <35 in UL <30 in LL NORMAL OR Reduced if Conduction Block PROLONGED (Temporal Dispersion) NMJ DISORDER NORMAL NORMAL NORMAL (REDUCED in Presynaptic ) NORMAL MYOPATHIC NORMAL NORMAL NORMAL (REDUCED in Severe Distal) NORMAL

34. F-response First described by Magaladery and McDougal. derives its name from Foot because it was first recorded from the intrinsic foot muscles . This NCS evokes a small late response from a short duration supramaximal stimulation. It initiates an antidromic motor response to the spinal cord followed by an orthodromic motor response to the recording electrode.

35. F-wave study It is approximately 5% of CMAP amplitude The configuration and latency change with each stimulation. This is due to a polysynaptic response in the spinal cord, where Renshaw cells (R) inhibit impulses from traveling the same path each time.

36. click S upramaximal distal stimulation with cathode placed proximally to avoid the theoretic possibility of anodal block

37. This is not a reflex, as only motor pathway is involved F- waves latency can be used to derive CV of nerves between limb and spinal cord Uses: Early G BS C8- T1 , LS-S1 radiculopathy Polyneuropathy Limitation : only accesses motor fibers, not useful in sensory radiculopathies Mild Proximal Lesions: F-wave Normal Peroneal nerve can be difficult to elicit in normal subject Maybe absent in sleeping or sedated patient best obtained with distal stimulation, conduction across long segments will dilute its utility.

38. H - REFLEX named after Hoffmann , who first evoked the response in 1918 true reflex with a sensory afferent, synapse , and motor efferent segment stimulating the tibial nerve in popliteal fossa , recording the gastroc-soleus muscle prolonged H reflex in polyneuropathy, proximal tibial and sciatic neuropathy, lumbosacral plexopathy , lesions of S 1 nerve root

39. 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. The morphology of wave pattern and latency remains constant with each stimulation at the appropriate intensity.

40. H - REFLEX

41. F Response vs H reflex

42. Protocols at our lab- upper limb Median Ulnar Radial Axillary Musculo cutaneous Supra- spinatus MABC LABC Brachial Plexus M + S M + S M + S M M M S S F wave F wave CTS M + S M + S Plus comaprison studies at 3 sites for Median and ulnar muscles F wave F wave

43. Protocols at our lab- lower limb Tibial Peroneal Femoral Sup. Peroneal Sural Sapheneous LCN LS Plexopathy M M M S S S S Meralgia M M - S S - S F wave F wave

44. References values at our lab Motor ms mA m/s Latency Amplitude Velocity Median <4.2 >5 > 48 Ulnar <4 >5 > 48 Deep peroneal <6 >2 > 42 Posterior tibial <6 >5 > 42 Radial <2.9 >2 > 49 Musculocutaneous <5.7 Compare Axillary <4.9 Compare Suprascapular <3.7 Compare Femoral >3 Sensory uV Median <3.4 >15 > 48 Ulnar <3.4 >15 > 48 LABC <3 >15 > 50 MABC <3.2 >10 > 50 Superfical peroneal <3.4 >5 >42 Sural <3.4 >5 >42 Sapheneous <3.9 >2 > 40

45. Thank you