EDT EDT Special Populations & Considerations 1 — Questions and Answers
Question 1: When performing nerve conduction studies in neonates and infants, conduction velocities are expected to be:
- Similar to adult values due to full myelination at birth
- Approximately half of adult values, reaching adult levels by age 3–5 years (Correct answer)
- Faster than adult values due to smaller nerve diameter
- Highly variable and cannot be interpreted
Correct answer: Approximately half of adult values, reaching adult levels by age 3–5 years
Myelination is incomplete at birth; neonatal conduction velocities are approximately 50% of adult values and reach adult levels by age 3–5 years as myelination completes.
Question 2: In elderly patients, age-related changes in NCS include:
- Increased SNAP amplitudes and faster conduction velocities
- Reduced SNAP amplitudes, slightly slowed conduction velocities, and prolonged distal latencies (Correct answer)
- Absent CMAP responses bilaterally
- Markedly prolonged F-wave latencies with normal distal latencies
Correct answer: Reduced SNAP amplitudes, slightly slowed conduction velocities, and prolonged distal latencies
Normal aging causes gradual axonal loss and mild myelin changes, resulting in decreased SNAP amplitudes, mildly reduced conduction velocities, and slightly prolonged latencies.
Question 3: Which safety precaution is essential before performing nerve conduction studies in a patient with an implanted cardiac pacemaker?
- Pacemaker patients cannot have NCS under any circumstances
- Consult with cardiology and avoid stimulation over the chest or neck; keep currents distal and away from the pacemaker leads (Correct answer)
- Only perform sensory NCS and avoid all motor studies
- Increase stimulus intensity to achieve supramaximal stimulation quickly
Correct answer: Consult with cardiology and avoid stimulation over the chest or neck; keep currents distal and away from the pacemaker leads
NCS can be performed safely in pacemaker patients if stimulation is kept in the extremities, away from the pacemaker generator and leads, and with prior cardiology consultation if uncertain.
Question 4: In patients with lymphedema following mastectomy, EDX of the ipsilateral upper extremity requires caution because:
- NCS results will always show false-positive demyelination
- There is risk of introducing infection or worsening lymphedema with needle insertion; surface techniques are preferred (Correct answer)
- Conduction velocities are always faster in lymphedematous limbs
- All NCS responses will be absent
Correct answer: There is risk of introducing infection or worsening lymphedema with needle insertion; surface techniques are preferred
Needle EMG in a lymphedematous extremity post-mastectomy carries infection risk; the referring clinician should be consulted and non-invasive techniques prioritized where possible.
Question 5: EDX studies in pediatric patients may require sedation because:
- Nerve conduction velocities cannot be measured without sedation
- Movement and poor cooperation can produce artifact and make needle EMG technically unreliable (Correct answer)
- Sedation increases SNAP amplitudes in children
- Pediatric patients have absolute contraindications to awake NCS
Correct answer: Movement and poor cooperation can produce artifact and make needle EMG technically unreliable
Children may not cooperate with voluntary relaxation or contraction needed for EMG; movement artifact and lack of cooperation can significantly compromise study quality.
Question 6: In patients receiving anticoagulation therapy (e.g., warfarin), the primary concern with needle EMG is:
- Altered nerve conduction velocities due to medication
- Risk of bleeding, hematoma, or compartment syndrome, particularly in deep muscles (Correct answer)
- Complete inability to perform the study
- Electrical interference from the medication
Correct answer: Risk of bleeding, hematoma, or compartment syndrome, particularly in deep muscles
Anticoagulated patients have increased bleeding risk with needle EMG; deep muscles (paraspinals, iliopsoas) carry higher hematoma risk and should be approached cautiously.
EDT EDT Special Populations & Considerations 1
When performing nerve conduction studies in neonates and infants, conduction velocities are expected to be: