electrodiagnostics Flashcards
1
Q
What is an EMG
A
- 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
2
Q
Who performs EMG?
A
- 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
3
Q
Why do EDX studies
A
- 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
4
Q
Common reasons for NCS/EMG exam
A
- Symptoms
- numbness/tingling
- weakness
- extremity or radicular pain
- Physical findings
- reflex loss or asymmetry
- weakness
- sensory loss (touch, temp, proprioceptice)
- limip
- muscle atrophy
5
Q
What are the uses for EDX
A
- establish correct diagnosis
- localize the lesion
- determine tx if the diagnosis is already known
- provide info about prognosis
6
Q
When do you perform EDX studies
A
- 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
- examples:
7
Q
wallerian degeneration
A
- Degenerative changes which occur in the distal axonal segments and their myelin sheath secondary to proximal axonal injury or death of the cell body
8
Q
Describe the types of nerve injurys (SEDDON CLASSFICATION)
A
- 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
9
Q
CONTRAINDICATIONS for ordering a NCS/EMG
A
- 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
10
Q
Motor nerve conduction (CMAP_
A
- Stimulation of peripheral nerve while recording from a muscle innervated by that nerve
11
Q
sensory nerve conduction (SNAP)
A
stimulation of a sensory (cutaneous) or mixed nerve while recording froma mixed or cutaneous nerve
12
Q
Latency and amplitutde
A
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
13
Q
conduction velocity
A
- 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
- decreased limb temp
14
Q
Late responses
A
- 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
15
Q
H-Reflex
A
- 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
