EDT EDT EMG Waveform Analysis 1 — Questions and Answers
Question 1: Fibrillation potentials on needle EMG represent:
- Voluntary firing of normal motor units
- Spontaneous discharge of individual denervated muscle fibers (Correct answer)
- Fasciculation of an entire motor unit
- Normal insertional activity
Correct answer: Spontaneous discharge of individual denervated muscle fibers
Fibrillation potentials represent spontaneous discharges of single denervated muscle fibers that have become hyperexcitable after losing their nerve supply.
Question 2: Positive sharp waves (PSWs) on EMG are considered abnormal when:
- They occur only with needle insertion
- They persist beyond needle movement and occur spontaneously at rest (Correct answer)
- They appear during voluntary contraction
- They are seen only in paraspinal muscles
Correct answer: They persist beyond needle movement and occur spontaneously at rest
PSWs are abnormal when they occur spontaneously at rest beyond the area of needle insertion, indicating denervation or muscle membrane instability.
Question 3: Fasciculation potentials differ from fibrillation potentials in that fasciculations:
- Are smaller in amplitude and shorter in duration
- Represent spontaneous discharge of an entire motor unit (Correct answer)
- Occur only in denervated muscle fibers
- Are always pathological
Correct answer: Represent spontaneous discharge of an entire motor unit
Fasciculation potentials represent the spontaneous, involuntary discharge of an entire motor unit, appearing as complex polyphasic potentials of larger amplitude.
Question 4: Which EMG finding is most characteristic of chronic denervation with reinnervation?
- Small, short-duration polyphasic MUPs
- Large amplitude, long-duration polyphasic MUPs with reduced recruitment (Correct answer)
- Fibrillations with normal MUP morphology
- Early recruitment with normal MUP size
Correct answer: Large amplitude, long-duration polyphasic MUPs with reduced recruitment
Chronic denervation with reinnervation produces large-amplitude, long-duration polyphasic MUPs due to collateral sprouting and motor unit enlargement.
Question 5: The recruitment pattern in a myopathic process typically shows:
- Reduced recruitment with large MUPs
- Early recruitment with small, short-duration MUPs (Correct answer)
- Discrete pattern at maximal effort
- Absent voluntary activity
Correct answer: Early recruitment with small, short-duration MUPs
Myopathies reduce the force-generating capacity of individual muscle fibers, requiring more motor units to fire early to compensate, producing early recruitment of small MUPs.
Question 6: Complex repetitive discharges (CRDs) on EMG are best described as:
- Normal activity seen in healthy muscle at rest
- Uniform repetitive discharges with abrupt onset and cessation, indicating chronic muscle denervation or myopathy (Correct answer)
- Bursts of activity seen only during voluntary contraction
- High-amplitude potentials specific to ALS
Correct answer: Uniform repetitive discharges with abrupt onset and cessation, indicating chronic muscle denervation or myopathy
CRDs are uniform repetitive discharges with machine-gun-like quality that start and stop abruptly; they indicate chronicity in either neurogenic or myopathic conditions.
EDT EDT EMG Waveform Analysis 1
Fibrillation potentials on needle EMG represent: