ABEM (EDX) common mistakes
ABEM (EDX) · Understand the traps and how to avoid them.
On motor nerve conduction studies, accepting the first acceptable-looking waveform without confirming supramaximal stimulation and correct active/reference electrode placement, then reporting latency and amplitude from a submaximal or volume-conducted response.
Surface landmarks and color conventions are trusted, and a stable-looking waveform is assumed to be physiologic.
What to do instead
Increase stimulator output until CMAP amplitude no longer rises, verify an initial negative deflection with the active electrode over the motor point, and recheck the montage before measuring.
Reporting slowed conduction velocity or prolonged distal latency as demyelination without measuring skin temperature and warming a cool limb.
Cool limbs slow conduction and prolong latencies, yet temperature is often omitted from routine NCS workflow.
What to do instead
Measure skin temperature at the tested limb, warm to at least 32°C, document the value, and reinterpret the study after warming using temperature-appropriate reference values.
Starting voluntary activation immediately after needle insertion and skipping assessment of insertional and spontaneous activity at rest in each muscle.
Time pressure and focus on MUAP recruitment encourage moving directly to active contraction.
What to do instead
At each site, observe insertional activity, then allow the muscle to rest long enough to screen for fibrillations and fasciculations before asking for activation; sample multiple sites per muscle.
Diagnosing ulnar neuropathy at the elbow from a slowed across-elbow velocity alone without screening for Martin-Gruber anastomosis, ulnar sensory sparing, or conduction block.
Pattern recognition replaces a systematic check for anomalous innervation and focal demyelination.
What to do instead
Compare ulnar sensory versus dorsal cutaneous responses, ADM versus FDI, perform a median-ulnar anastomosis check, and use short-segment inching when across-elbow slowing is suspected.
Diagnosing cervical or lumbar radiculopathy from limb needle findings without paraspinal EMG or myotomal mapping, missing a plexopathy or generalized neuropathy.
Incomplete needle sampling and overreliance on one abnormal limb muscle create a false localizing pattern.
What to do instead
Include paraspinal muscles and test muscles sharing a root but innervated by different peripheral nerves; correlate with NCS and expected myotomal distribution.
Using a single conduction velocity cutoff to diagnose demyelination while ignoring conduction block, temporal dispersion, prolonged distal latency, or F-wave minimum latency.
Memorized cutoff values are easier than applying multiple parameters, and axonal loss can also reduce velocity.
What to do instead
Apply formal demyelinating criteria across multiple parameters and nerve segments, including proximal stimulation and F-waves, and avoid labeling purely axonal slowing as demyelination.
Leaving default filter settings unchanged so that low-frequency filters clip the CMAP or high-frequency filters obscure fibrillation potentials.
Default machine settings are assumed to be appropriate for every nerve and muscle study.
What to do instead
Know standard NCS and EMG filter settings, adjust them for the specific study, verify waveform reproducibility and noise, and document any nonstandard settings.
Judging MUAP duration, amplitude, and phases from a single strong contraction rather than isolating individual units at low effort.
High effort produces an interference pattern with overlapping units that cannot be measured reliably.
What to do instead
Ask for gentle contraction, isolate single MUAPs, measure duration, amplitude, and phases/turns, then assess recruitment frequency and interference pattern separately.
Inserting needle EMG into chest, neck, or paraspinal muscles without reviewing danger zones for pleura, lung, or major vessels.
Attention is on muscle localization rather than cross-sectional anatomy and procedural risk.
What to do instead
Review cross-sectional anatomy before sampling high-risk regions, use bony landmarks, avoid deep blind insertion near the pleura, and use ultrasound guidance when anatomy is uncertain.
Issuing an EDX report whose conclusions are unsupported by documented technical details, reference values, temperature, and study limitations.
Copy-paste templates and focus on the impression lead to incomplete documentation.
What to do instead
Use a structured report that records technical parameters, temperature, reference values, limitations, and explicit correlation with the clinical question, and submit it for quality review.