repetitive nerve stimulation

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seminar on repetitive nerve stimulation physiology,application in various neuromuscular disorders

seminar on repetitive nerve stimulation physiology,application in various neuromuscular disorders

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  • 1. Repetitive Nerve Stimulation
  • 2. Plan of the talk
    • Physiology of Neuromuscular junction
    • Procedure, technical aspects
    • Interpretation
    • Application in various conditions
  • 3.  
  • 4.  
  • 5. definitions
    • Quantum. A quantum is the amount of Ach packaged in a single vesicle.
    • Each quantum (vesicle) 1 mV change of postsynaptic membrane potential.
    • Rest, MEPP
    • The number of quanta released after a nerve action potential depends on the number of quanta in the immediately available (primary) store and calcium stores
    • Normally 50-300(60) vesicles
  • 6. definitions
    • End plate potential -EPP is the potential generated at the postsynaptic membrane following a nerve action potential and neuromuscular transmission.
    • 60 mV change in the amplitude of the membrane potential.
    • Safety factor. The safety factor of neuromuscular transmission is simply defined as the difference between the EPP and the threshold potential for initiating an action potential.
    • MFAP
    • CMAP
  • 7. Calcium and quanta dynamics
    • calcium :diffuses slowly out of the presynaptic terminal in 100–200 msec.
    • Ach stores: immediately available (primary) store and secondary (or mobilization) store
    • Inter stimulus interval
    • rapid RNS (more than every 100 msec, or stimulation rate >10 Hz), calcium influx is greatly enhanced and the probability of release of Ach quanta increases.
  • 8. Potentiation
    • voluntary activation or high frequency stimulation
    • CMAP amp increases
    • Facilitation-recruitment
    • Pseudo facilitation-synchronisation of muscle activity
  • 9.  
  • 10. Relationship -EPP,AP,CMAP
  • 11. Neuromuscular junction disorders
    • Post synaptic
    • Myasthenia gravis
    • Organophosphorus poisoning
    • Curare induced paralysis
    • Congenital Myasthenic syndromes
    • Presynaptic
    • Botulism
    • LEMS
    • Magnesium induced paralysis
    • Combined defect
    • Gallamine, amino glycoside antibiotics,
    • quinine, suxamethonium.
  • 12. Repetitive nerve stimulation ( RNS)
    • Jolly in 1895 first described progressive reduction in visible muscle contraction in MG (Myaesthenic reaction)
    • Harvey and Masland(1941) reported electrical decremental muscle response on repetitive motor nerve stimulation.
    • Ekstedt in 1964 described SFEMG
  • 13. RNS- technique
    • RNS is technically demanding procedure.
    • Poor electrode placement, sub maximal stimulation, movement artifacts, causes false positive results
    • Minimise artifacts
    • Immobilisation
  • 14. RNS-technique
    • RNS is performed on selected motor nerves with recording by surface electrodes.
    • G1-motor point,G2-tendon
    • Supramaximal stimulus
    • Initial sharp negative deflection
  • 15. Muscle selection
    • Clinically weak muscles should be selected.
    • Usually facial and proximal limb muscles shows greater abnormality than distal muscles.
    • Nerves involved in other diseases should be avoided.
    • Cholinesterase inhibitors should be stopped 12-24 hrs before.
  • 16. Machine setup for RNS 30-50 Stimulus rate -high <5 Stimulus rate -low 0.1 Stimulus duration (msec) 2-3 High filter (KHz) 2-5 Low filter (Hz) 2 Sweep time (ms/div) 2-5 Sensitivity (mV/div)
  • 17. temperature
    • Cooling can cause false negative results.
    • Hand/foot muscles at 34c.
    • Proximal/facial muscles need not be warmed
    • Decrement is greater at 44c than at 22c
  • 18. Effect of temperature on RNS
  • 19. Stimulus technique
    • Best at 3-5 hz
    • Decrement increases with stimulus rates up to 10hz.
    • Higher rates cause movement artifacts and painful
    • Pseudo facilitation
  • 20. Effect of different stimulation rates
  • 21. Activation
    • Maximal voluntary contraction
    • 10 -30 sec for post exercise increment of baseline CMAP
    • 60 seconds of exercise
    • High frequency stimulation 20-50hz
    • Trains of low frequency stimulus at end of activation and one minute intervals for 5 minutes
    • Post activation exhaustion
    • l
  • 22.  
  • 23.  
  • 24. Measurement technique
    • Peak to peak
    • Negative peak amplitude
    • Display setting 50-100msec/screen can detect technical problems
    • Change in CMAP size
    • D4 =(V4 – V1)/V1 * 100
    • Area vs amplitude
  • 25. Slow RNS
    • supra maximal CMAP
    • 3–5 stimuli to a mixed or motor nerve at a rate of 2–3 Hz.
    • slow enough to prevent calcium accumulation, high enough to deplete the quanta
    • maximal decrease in Ach release occur after the first four stimuli
    • reproducible decrement
    • exercises for 10 seconds to demonstrate repair of the decrement (‘‘post-exercise facilitation’’)
    • No decrement-1 minute max voluntary exercise –post exercise exhaustion
  • 26. Slow RNS
  • 27. Rapid RNS
    • optimal frequency is 20–50 Hz,for 2–10 seconds
    • brief (10-second) period of maximal voluntary isometric exercise has,the same effect as rapid RNS
    • Depletion of quanta vs calcium accumulation
    • Incremental response in LEMS
  • 28. Rapid RNS
  • 29. Patterns of response to slow RNS
  • 30. Activation cycle in MG
  • 31. Criteria for abnormal decrement
    • Normal muscle -8% decrement at 3-5hz
    • 1.Reproducibility
    • 2.Envelope shape
    • 3.Activation cycle
    • 4.Response to edrophonium
  • 32. RNS in pre and post synaptic disorders Decrement or normal Increment High rate RNS Decrement Present Present Decrement Present Absent
    • Low rate RNS
    • Resting
    • Post exercise facilitation
    • Post exercise exhaustion
    Normal Small CMAP amplitude Post-synaptic Pre-synaptic Parameter
  • 33. Double step RNS
    • Desmedt and Borenstein.
    • First step: 3-Hz supramaximal ulnar nerve stimulation for 3 minutes with recording of electrical response of hand and forearm muscles.
    • Second step: procedure is repeated with circulation arrested by inflated blood pressure cuff at 250 mm Hg placed proximal to stimulation.
    • Rarely used .
  • 34. Regional curare test
    • Small dose (0.2 mg) of D-tubocurarine is injected into arm rendered ischaemic by blood pressure cuff around arm.
    • RNS is done after several minutes of ischaemia.
    • More sensitive.
    • Potentially dangerous.
    • Rarely used.
  • 35. SFEMG
  • 36. Jitter and block
  • 37. Myasthenia gravis
  • 38. Electrophysiological investigation
    • Nerve conduction studies-usually normal (low CMAP in LEMS)
    • Concentric needle EMG-usually normal
    • Repetitive nerve stimulation
    • Single fiber EMG
  • 39. RNS
    • Most commonly used test, easy.
    • RNS is relatively insensitive,10-50% in ocular myastenia,75% in generalised MG
    • RNS is relatively specific(90%)
    • SFEMG is Most sensitive.(90% in ocular,95% in MG)
    • Normal baseline CMAP
    • Greater than 10% decremental response at rest and post exercise
    • No role for high frequency stimulation
  • 40.  
  • 41. Baseline and 10sec exercise
  • 42. 60sec exercise-exhaustion
  • 43. Congenital Myasthenic Syndromes
    • Newborns of non-Myasthenic mothers.
    • No Ach R antibodies.
    • Respiratory distress, feeding difficulty, Ptosis are common.
    • Decremental response on 2 Hz RNS, abnormal SF-EMG.
    • End plate acetyl cholinesterase deficiency and slow channel syndrome , a repetitive CMAP is elicited by a single supramaximal stimulus.
  • 44. Repetitive CMAP
  • 45. Lambert Eaton Myasthenic Syndrome (LEMS )
    • Weakness and fatigability of proximal muscles.
    • Relative sparing of EOM, bulbar muscles.
    • Hyporeflexia
    • Dry mouth
    • Associated with SCC lung
    • Antibodies against VGCC (voltage gated calcium channel)
  • 46. LEMS
  • 47. LEMS
    • Distal muscles RNS preferred
    • 3 pattern recognized
    • Low normal CMAP amplitude, decremental response at low rate RNS, normal at high rate.
    • Low CMAP amplitude, decremental response at low rate, and incremental response at high rate RNS (>100%)—classical triad .
    • Low CMAP amplitude, decremental low rate RNS, initial decrement at high rate RNS.
  • 48. Incrementing response after brief exercise (10-15 sec) in LEMS. Increment is 10-fold, with CMAP of 3.2 mV. CP CMAP amplitude is 0.35 mV (normal >1 mV).
  • 49. Incremental response in LEMS
  • 50. 50hz RNS-increments
  • 51. Botulism
    • Defective release of Ach from nerve terminals.
    • It cleaves synaptic vesicle protein.
    • Extra ocular and bulbar weakness  limb and respiratory weakness.
    • Blurred vision, dilated pupil, constipation, urinary retention.
    • Electro physiologically resemble LEMS
  • 52. Botulism
    • Reduced CMAP in at least two muscles
    • At least 20 percent CMAP amplitude facilitation on tetanic stimulation
    • Persistance of facilitation atleast 2 minutes after activation
    • No postactivation exhaustion
  • 53. Miscellaneous conditions
    • Amyotophic lateral sclerosis
    • Oculopharyngeal dystrophy
    • Drugs(aminoglycosides,Anaesthetic,Beta blockers)
    • Hypermagnesemia
    • Organophosphate
    • Seasonal myaesthenic syndromes
  • 54.  
  • 55.  
  • 56.  
  • 57.
    • Thank you
  • 58. References
    • American Association of electrodiagnostic medicine-Practice parameters on RNS
    • Aminoff text book of electrophysiology
    • Amato NMJ disorders
    • Jun Kimura 2 nd ed
    • Shapiro
    • emedicine –web md
  • 59. Thank you