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  • When we talk about respiratory muscle EMG, we tend to think immediately of the diaphragm, which is the main muscle of inspiration during tidal or resting breathing.
    There are 3 principal methods for EMG sampling of the diaphragm:
    With a substernal approach, the needle is inserted midline just inferior to the xyphoid process, passes through the rectus abdominus muscle and under the xyphoid, then is guided tightly along the posterior surface of the sternum until the diaphragm is reached;
    A subcostal approach can also be used, where the needle is inserted at the costal margin under the 9th costal cartilage, then through the abdominal muscles, and again guided along the posterior aspect of the rib cage until the costal portion of the diaphragm is reached;
    And finally, there is the intercostal approach, which is the one we use and which really gives you the best return of information for the cost of one needle poke. This technique was first describe by Koepke some 40+ years ago, and more recently reviewed by Charles Bolton in a 1993 AAEM minimonograph. Here the needle is insertedperpendicular to the skin at a point midway between the anterior axillary and medial clavicular linesat the level of the 8th or 9th intercostal space, and just above the costal margin.


  • 1. An approach to diagnosing ALS emphasizing Clinical Neurophysiology Sociedad Mexicana de Neurofisiología Clínica, A.C Dr. Andrew Eisen MD.,FRCPC Profesor Emérito Universidad de British Columbia
  • 2. Electrodiagnostic criteria for diagnosis of ALS Clinical Neurophysiology 119 (2008) 497–503 Mamede de Carvalho, Reinhard Dengler, Andrew Eisen, John D. England, Ryuji Kaji, Jun Kimura, Kerry Mills, Hiroshi Mitsumoto, Hiroyuki Nodera, Jeremy Shefner, Michael Swash.
  • 3. Awaji consensus 1. Edx and clinical data are of equal and interchangeable value in diagnosing ALS 2. In the presence of signs of partial denervation, Fasciculations (preferably of complex morphology) are equivalent to fibs-psw, indicating ongoing denervation. 3. Unstable MUPs & FPs are especially relevant
  • 4. Positive sharp waves Fibrillation CRD Large complex unstable MUPs Seek these EMG abnormalities in clinically normal muscles
  • 5. ALS Fasciculation • More diffuse and profuse • Clinically large excursions • EMG - potentials complex, unstable, components “come and go” • Origin - supra-spinal • May be glutamate dependent - reduced by riluzole and neurontin
  • 6. ALS Fasciculation More than one motor unit
  • 7. Benign Fasciculation • Intermittent • Caffeine, fatigue, post-exercise, tobacco • Clinically small excursions • EMG - potentials simple, stable, components remains constant • Origin - nerve terminal
  • 8. MUP recruitment Early normal recruitment Normal maximum effort ALS
  • 9. Marked conduction block MMN Typically proximal upper limb with paretic, normal bulk (fasciculating) muscle and reflex loss in affected myotome No sensory loss
  • 10. CIDP showing progressive dispersion and block
  • 11. Initial Clinical Presentations (1813 patients) • Dysarthria (32.8%) • Hand dysfunction (19.7%) • Shoulder dysfunction (13.6%) • Foot drop (12.5%) • Fasciculation/cramp (11.4%) • Spastic gait (4%) • Respiratory failure (4%) • Frontal dementia (2%)
  • 12. Clinical Features Largely Inconsistent with ALS • Sensory impairment • Autonomic dysfunction • Eye movement abnormalities • Movement disorders • Cognitive impairment - Alzheimer type • LMN signs with symmetrical onset But all can occur in ALS
  • 13. Incorrect Diagnosis (7.1%) Cervical spondylotic myelopathy (2.1%) Multifocal motor-neuropathy (1.8%) Monomelic amyotrophy (1.1%) Progessive spinal MS (0.6%) Painless radiculopathy (0.6%) CIDP (0.5%) Kennedy’s disease (0.3%) Inclusion body myositis (0.2%)
  • 14. Dysarthria - differential • Multiple silent stroke – MRI (unidentified bright objects common >60’s) • Myasthenia gravis/MUSK (Muscle-specific kinase receptor) – ACh receptor antibodies, SFEMG (jitter can be marked in ALS) • Brain stem tumour – MRI • Other system degenerations
  • 15. Dysarthria and Bulbar Onset • Tongue clinical-electrical fasciculation and fibrillation • TMS to trapezius and other bulbar muscles • Limb muscle LMN findings/fasciculation • TMS - high threshold, normal CCT
  • 16. Hand Dysfunction – Wasted hand (Clinical Considerations) • Intramedullary lesions • Cervical stenosis (central bar at C3/4 with secondary hand wasting) • Motor neuropathy (more commonly proximal) • Neurogenic TOS (young women) • CTS – Elderly persons – Painless thenar wasting
  • 17. Shoulder Dysfunction • Cervical Disc Disease – Acute, sub-acute, painful – Usually one myotomes – Fasciculation rather rare – EMG one/two myotomes • (paraspinal > limb)
  • 18. Shoulder Dysfunction • ALS – Gradual, painless – Multi-myotomal (pectoralis muscle) – Fasciculation prominent – EMG multimyotomal • (limb > paraspinal)
  • 19. Flail (floppy) arm
  • 20. Foot Drop • Peroneal palsy – Acute onset, complete, sensory deficit – Conduction block with conduction slowing across fibular head – Reduced absent peroneal SNAP – EMG abnormalities restricted to peroneal innervated muscles
  • 21. Foot Drop • L4/5 radiculopathy – Incomplete, pain, sensory deficit – Normal SNAP, – Paraspinal > limb EMG abnormalities, fasciculation rare
  • 22. Foot Drop • ALS – Gradual, painless, incomplete – Multimyotomal S1/2 as well as L4/5 (flail foot – not a foot drop +/- spastic gait – Fasciculation – EMG multimyotomal (limb > paraspinal) – Normal SNAPs
  • 23. Late onset foot-drop muscular dystrophy with rimmed vacuoles • Autosomal dominant inheritance • Begins in 5th -6th decade • Initial symptom uni-or bilateral MILD foot drop • Tibial muscles atrophic but long and short foot extensors spared • Normal sensation
  • 24. 3 FROM MAHJNEH, I ET AL NEUROLOGY. 61(1):87- 92, JULY 8, 2003.
  • 25. Spastic Gait (In the ALS age group) • Spondylotic myelopathy • Primary lateral sclerosis • “Old folks” MS • Occult hydrocephalus – In the above - fasciculation and neurogenic changes absent and babinski positive
  • 26. ALS Gait • Gait more hesitant than spastic • Hyper-reflexia with NEGATIVE babinsky • Neurogenic EMG
  • 27. Documenting Upper Motor Neuron Disease in ALS Cortical threshold Central conduction Cortical silent period Repetitive (double) TMS Peristimulus time histograms (PSTHs) Triple stimulation Threshold tracking
  • 28. Disease Duration (months) Stimulus threshold (%) ALS (N = 42)
  • 29. ALS Normal Cortical Silent Period
  • 30. Normal ALS 2 ms 3 ms 5 ms 10 ms Subthreshold conditioning stimulus Yokota et al , 1996
  • 31. Triple Stimulation a good measure of cortical neuronal loss Abductor digiti minimi Abductor hallucis
  • 32. Onset with Respiratory Failure Patients usually in ICU for respiratory failure and cannot be weaned off the respirator Careful exam reveals long-tract signs and fasciculation EMG of chest wall and diaphragm are very helpful
  • 33. • Phrenic nerve conduction – of limited value with only modest slowing late in disease • The diaphragmatic CMAP – becomes reduced with disease progression but this is an unreliable measure in ALS. • Cortico-diaphragmatic conduction using TMS – may be a sensitive measure revealing subclinical diaphragmatic impairment although not correlated to other respiratory measures
  • 34. Diaphragm EMG Substernal Intercostal Diaphragm
  • 35. Stabs C u t s M O N O P O L A R
  • 36. Monopolar needle ◦ More comfortable ◦ Safer for diaphragm does not tear 7th /8th intercostal space (or lower) in anterior axillary line (cartilage formation in older subjects) Needle will go through ◦ External oblique ◦ Intercostals ◦ Diaphragm
  • 37. 7th -8th interspace
  • 38. Abdominal Wall Weakness • Fasciculations of abdominal wall • Abdominal cramping when bending over (i.e. tying shoe laces) • Active denervation of abdominal muscles
  • 39. Recognition of “look-alikes” Kennedy’s disease Motor neuropathy with conduction block Inclusion body myositis HTLV1 and 2 Hereditary spastic paraplegias It is OK to consider ALS early but the diagnosis should be continually reviewed !!!