EDT EDT Special Populations & Considerations 2 — Questions and Answers
Question 1: When performing EDX studies in a patient with suspected acute Guillain-Barré syndrome within the first week of symptom onset, results may be:
- Always dramatically abnormal from day one
- Initially normal or show only subtle F-wave abnormalities, as demyelination evolves over days to weeks (Correct answer)
- Consistent with a pure axonal pattern immediately
- Show marked denervation on needle EMG within 24 hours
Correct answer: Initially normal or show only subtle F-wave abnormalities, as demyelination evolves over days to weeks
In early GBS, EDX changes lag behind clinical presentation; absent or prolonged F-waves may be the only early finding, with full demyelinating pattern emerging over 1–4 weeks.
Question 2: In a patient with end-stage renal disease on hemodialysis, expected EDX findings include:
- Focal entrapment neuropathies only
- Length-dependent axonal sensorimotor polyneuropathy (uremic neuropathy) (Correct answer)
- Pure demyelinating neuropathy
- Normal EDX in all patients on dialysis
Correct answer: Length-dependent axonal sensorimotor polyneuropathy (uremic neuropathy)
Uremic neuropathy is a length-dependent axonal sensorimotor polyneuropathy caused by accumulation of uremic toxins, with distal sensory nerves affected earliest.
Question 3: In evaluating a patient with chemotherapy-induced peripheral neuropathy (CIPN), EDX typically shows:
- Proximal demyelinating polyneuropathy
- Length-dependent axonal sensory-predominant polyneuropathy affecting distal SNAP amplitudes earliest (Correct answer)
- Normal NCS with myopathic EMG
- Multifocal motor neuropathy
Correct answer: Length-dependent axonal sensory-predominant polyneuropathy affecting distal SNAP amplitudes earliest
Most chemotherapy agents (taxanes, platinum compounds, vinca alkaloids) cause length-dependent axonal sensory-predominant neuropathy, with sural SNAP amplitude reduction being an early and sensitive finding.
Question 4: For EDX evaluation of a patient with obesity (BMI >40), a key technical adjustment is:
- Decreasing stimulus intensity to prevent discomfort
- Increasing stimulus intensity and potentially needle electrode placement for NCS to achieve supramaximal stimulation through thick tissue (Correct answer)
- Avoiding all sensory nerve studies
- Using only bipolar surface electrodes for EMG
Correct answer: Increasing stimulus intensity and potentially needle electrode placement for NCS to achieve supramaximal stimulation through thick tissue
Increased subcutaneous fat in obese patients attenuates electrical stimulation; higher intensities are needed to depolarize deep nerves, and near-nerve needle stimulation may be necessary.
Question 5: EDX evaluation of a patient with bilateral carpal tunnel syndrome superimposed on diabetic polyneuropathy is challenging because:
- Carpal tunnel syndrome does not occur with diabetes
- Diabetic neuropathy may reduce baseline sensory amplitudes and slow conduction, making superimposed CTS difficult to isolate without comparison studies (Correct answer)
- Diabetes accelerates NCS conduction velocities
- Needle EMG is contraindicated in diabetics
Correct answer: Diabetic neuropathy may reduce baseline sensory amplitudes and slow conduction, making superimposed CTS difficult to isolate without comparison studies
Diabetic polyneuropathy reduces baseline SNAP amplitudes and mildly slows conduction; identifying additional focal slowing at the wrist (CTS) requires careful comparison of median versus ulnar responses.
Question 6: In a patient with bilateral lower extremity amputations, evaluation of peripheral neuropathy EDX strategy should include:
- Upper extremity NCS only, which is sufficient to diagnose polyneuropathy
- Upper extremity NCS (median, ulnar, radial sensory and motor), sural at the stump if accessible, and EMG of residual limb muscles (Correct answer)
- Only H-reflexes at the knee level
- No EDX is possible in amputees
Correct answer: Upper extremity NCS (median, ulnar, radial sensory and motor), sural at the stump if accessible, and EMG of residual limb muscles
Upper extremity NCS can diagnose polyneuropathy and assess severity; if stump is accessible, residual nerve studies and EMG of residual limb muscles can provide additional information.
EDT EDT Special Populations & Considerations 2
When performing EDX studies in a patient with suspected acute Guillain-Barré syndrome within the first week of symptom onset, results may be: