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repetitive nerve stimulation

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

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repetitive nerve stimulation

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

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