R.NCS.T common mistakes
R.NCS.T · Understand the traps and how to avoid them.
Reporting a sensory nerve action potential amplitude without correcting for the fact that the active and reference electrodes are close together, so the recorded amplitude is smaller than the true nerve response, and then calling a normal study abnormal.
Candidates memorize raw amplitude cutoffs from textbooks and forget that surface near-nerve recording attenuates SNAP amplitude relative to the true nerve potential; they also forget that SNAP amplitudes vary with age and temperature.
What to do instead
Always record limb temperature, apply a temperature correction or warm the limb to a standard value, and interpret SNAP amplitude against the laboratory's own normative values for that nerve, technique, and age band rather than a single remembered cutoff.
Onset latency is marked at the first deflection of the waveform rather than at the true takeoff, or peak latency is used interchangeably with onset latency when calculating conduction velocity.
Candidates rush cursor placement on low-amplitude or noisy traces, and they confuse onset latency (used for conduction velocity) with peak latency (used for comparison to normative peak values).
What to do instead
Use a consistent, reproducible cursor rule: place the onset cursor at the first reproducible departure from baseline on an averaged, low-noise trace, and state explicitly which latency type is being reported for each measurement.
Interpreting an absent or reduced sensory response in an older patient as definite pathology without checking the age-adjusted normative limit and without confirming the response is truly absent versus technically inadequate.
Candidates apply young-adult normative values to elderly patients, and they do not verify electrode placement, gain, and averaging before declaring a response absent.
What to do instead
Before calling a response absent, confirm electrode placement and impedance, increase averaging, and check the age-matched normative range; document the technical adequacy of the study alongside the interpretation.
Confusing the F-wave with a true motor conduction measure and reporting an F-wave latency as if it directly reflects proximal conduction velocity.
Candidates memorize that F-waves assess proximal segments but do not understand that F-wave latency reflects the entire round-trip pathway and is strongly influenced by limb length and height.
What to do instead
Report F-wave minimum latency and chronodispersion against height-adjusted normative values, and describe it as an index of proximal conduction rather than a direct velocity measurement; pair it with other proximal measures when possible.
Setting SEP stimulation intensity or averaging parameters identically across all patients without adjusting for limb size, skin impedance, or noise level, then interpreting a poorly formed waveform as abnormal.
Candidates copy a standard protocol and do not appreciate that SEP waveform quality depends heavily on stimulation intensity relative to motor threshold, electrode impedance, and number of averages.
What to do instead
Verify supramaximal or adequate stimulation, keep impedances low, and increase the number of averages until the waveform is reproducible on repeat runs before interpreting latency or amplitude.
Interpreting an absent cortical SEP as a definite abnormality without confirming that the peripheral and subcortical components are present and that the study is technically adequate.
Candidates focus on the final cortical response and skip the stepwise check of peripheral, plexus, and subcortical peaks that would reveal a technical or peripheral cause.
What to do instead
Analyze SEPs in a stepwise fashion from peripheral to cortical, and only attribute an absent cortical response to central pathology when all proximal components are present and reproducible.
Performing or interpreting transcranial magnetic stimulation without screening for contraindications such as implanted devices, metal hardware near the head, or a history of seizures.
Candidates treat TMS as a routine test and skip the safety checklist, or they assume a screening form completed once is sufficient for all sessions.
What to do instead
Complete a structured contraindication screen before every TMS session, document the screen, and have a written seizure-management protocol in place before stimulation begins.
Confusing the roles of the resting motor threshold and the stimulation intensity used for motor evoked potential amplitude, and reporting an MEP amplitude without stating the stimulation intensity relative to threshold.
Candidates learn that motor threshold is determined by the lowest intensity producing a response but do not connect that threshold to how subsequent MEP amplitudes must be normalized.
What to do instead
Determine resting motor threshold with a defined criterion, report all MEP amplitudes as a function of stimulus intensity expressed relative to threshold, and keep stimulation parameters consistent across serial studies.
Misidentifying which nerve root or plexus element is being studied because the candidate relies on electrode placement alone and does not verify the expected innervation pattern and response characteristics.
Candidates memorize electrode locations without understanding the underlying anatomy, so a misplaced electrode or an anomalous innervation pattern goes unrecognized.
What to do instead
For every study, state the expected innervation, verify the response is consistent with that nerve, and check for common anatomic variants (for example, Martin-Gruber or accessory nerve connections) before interpreting.
Failing to document informed consent, patient identification, and the specific study performed, or documenting results in a way that cannot be reproduced by another technologist.
Candidates focus on the technical procedure and treat documentation as an afterthought, and they may not know the professional standard for what a nerve conduction report must contain.
What to do instead
Use a structured report template that captures patient identification, consent, limb temperature, electrode sites, stimulation parameters, raw values, and interpretation, and review it against the laboratory's documentation standard before signing.