electrodiagnostics

Question 1

What is an EMG

Answer 1

• Purpose: is there a problem in the PNS and where the problem is
• Key points;
  
  • electrodiagnosis is a complete examination, not simply a test and must be interpreted in accordance with the entire clinical picture
  • The more you know about the basic anatomy of the nerves and muscles, the easier it will be to learna bout and interpret eletrodiagnostic studies

Question 2

Who performs EMG?

Answer 2

• Physiatrists (PM&R)
  
  • proficiency in electrodiagnosis is required for residency completion
• Neurologists
  
  • can pursue extra-year fellowship training after residency
• Physical therapist/technicians
  
  • in some select circumstances

Question 3

Why do EDX studies

Answer 3

• Important method to distingish between many peripheral nerve and muscle disorders
• Represents a PHYSIOLOGIC piece of the diangoist puzzle
  
  • real time inforamtion about what is happening physiologically with respect to the nerve and muscle

Question 4

Common reasons for NCS/EMG exam

Answer 4

• Symptoms
  
  • numbness/tingling
  • weakness
  • extremity or radicular pain
• Physical findings
  
  • reflex loss or asymmetry
  • weakness
  • sensory loss (touch, temp, proprioceptice)
  • limip
  • muscle atrophy

Question 5

What are the uses for EDX

Answer 5

• establish correct diagnosis
• localize the lesion
• determine tx if the diagnosis is already known
• provide info about prognosis

Question 6

When do you perform EDX studies

Answer 6

• EMG or NCS should NOT be performed prior to 21 days after the injury or onset of symptoms
  
  • examples:
    
    • herniated disc
    • pinches a nerve root (radiculopathy)
    • immediate sciatica symtpoms
    • axonal nerve injury can slowly spread down the entire length of the nerve

Question 7

wallerian degeneration

Answer 7

• Degenerative changes which occur in the distal axonal segments and their myelin sheath secondary to proximal axonal injury or death of the cell body

Question 8

Describe the types of nerve injurys (SEDDON CLASSFICATION)

Answer 8

• Neurapraxia (MILD)
  
  • failure of nerve conduction across the affected nerve segment combined with normal nerve conduction above and below the segment
  • NO WALLERIAN DEGENERATION INVOLVED
  • carred good prognosis
• Axonotmesis (more significant compression)
  
  • disruption of axon continuity with wallerian degeneration, but perineurium and/or endoneurium are still intact
• Neurotmesis
  
  • severance of nerve; carries poor prognosis and surgical repair is needed for functional recovery

Question 9

CONTRAINDICATIONS for ordering a NCS/EMG

Answer 9

• STRICT
  
  • Severe bleeding disorder/anticoagulation out of control
  • NCS contraindicated in patients with AUTOMATED IMPLANTED CARDIAC DEFIBRILLATOR (AICD)
  • Active skin/soft tissue infection (cellulitis)
• Relative
  
  • axillary lymph node dissection after mastectomy
  • patient needing muscle biopsy

Question 10

Motor nerve conduction (CMAP_

Answer 10

• Stimulation of peripheral nerve while recording from a muscle innervated by that nerve

Question 11

sensory nerve conduction (SNAP)

Answer 11

stimulation of a sensory (cutaneous) or mixed nerve while recording froma mixed or cutaneous nerve

Question 12

Latency and amplitutde

Answer 12

LATENCY = interval between the stimulus and the onset of the response

AMPLITUDE = maximum voltage difference between two points

• it is proportional to the number and size of nerve fibers that are depolarized
• provides an estimate of the amount of nerve tissue that is electrically active

Question 13

conduction velocity

Answer 13

• the speed at which the nerve fibers are carrying the electrical stimulus between two sites
• comparison of conduction between two segments of the same nerve can localize a lesion
• Factors affecting conduction
  
  • AGE
  • Temperature
    
    • decreased limb temp
      
      • latency = prolonged
      • amplitude = increased
      • CV = decreased

Question 14

Late responses

Answer 14

• Late responses = F wave and H reflex
• most useful for dtecting PROXIMAL NERVE PATHOLOGIES
• especially ear in disease
  
  • F wave is useful in guillain barre syndrome

Question 15

H-Reflex

Answer 15

• Due to MONOSYNAPTIC SPINAL REFLEX
• primary value is in distinguishing S1 from L5 radiculopathies
  
  • often this is difficult with physical exam and even EMG as L5 and S1 have overlapping myotomes
  • HOWEVER, in S1 radiculopathy, the H reflex with be abnormally slow when compared to non-involved limb

Question 16

EMG (electromyography)

Answer 16

• Displays a “real-time” picture (on screen) and a sound (speaker) of the electrical activity of the muscle membrane

Question 17

voluntary, insertional, spontaneous activity

Answer 17

• Voluntary - patient moves on their own
• insertional activity
  
  • caused by insertion or movement of a needle electrode
• spontaneous actiity (pathologic)
  
  • fibrillations potentials, positive sharp waves