2025 Workshop Handout Bundle-W21RTA NCS Pitfalls

W21RTA NCS Pitfalls - Bassam
Pdf Summary
The document "NCS Pitfalls" by Dr. Bassam A. Bassam focuses on common technical and physiological pitfalls in nerve conduction studies (NCS) and offers guidance to avoid diagnostic errors. NCS—used to evaluate motor and sensory nerve function—appear straightforward, but various factors can cause artifacts that lead to incorrect interpretations.<br /><br />Instrumentation issues include improper amplifier settings, filters, and electrode placement. Incorrect amplifier sensitivity and filter frequencies can distort nerve action potentials (SNAPs and CMAPs), affecting amplitude, latency, and waveform shape. Optimal active and reference electrode placement is vital: sensory studies typically use a 3-4 cm interelectrode distance to maximize signal and avoid phase cancellation; motor studies require positioning the active electrode over the muscle motor point to ensure accurate latency and amplitude recordings. Electrode instability can introduce artifacts, affecting amplitude and waveform shape, especially during repetitive stimulation.<br /><br />Stimulating electrode errors involve excessive stimulus intensity causing activation of adjacent nerves or enlarging the nerve depolarization zone, leading to abnormal latencies or false negative/positive findings. Stimulus artifact, a large electrical disturbance from stimulation, can interfere with recordings if not minimized by proper skin preparation, electrode arrangement, and anode rotation.<br /><br />NCS determinations must consider amplitude variability due to distance and physiological differences, importance of measuring distances accurately (favoring longer interstimulus distances), and the need to replicate normative data collection parameters for valid comparisons. Anomalies such as Martin-Gruber and accessory deep peroneal nerve communications can mimic pathology and must be recognized.<br /><br />Physiologic factors significantly influence NCS. Temperature is critical: cooling prolongs latencies, lowers conduction velocity, and alters amplitudes, potentially leading to misdiagnosis. Limb warming is essential before testing. Age affects nerve conduction velocity and amplitudes, particularly after age 60. Gender and height have minor or debated influences. Central nervous system facilitation modulates reflexes like the H-reflex, affecting amplitude but not latency, so facilitation maneuvers may be needed to avoid false-negatives.<br /><br />In conclusion, the article emphasizes that meticulous attention to technical setup, electrode placement, patient physiology, and awareness of anatomical variants are crucial for reliable NCS interpretation and accurate diagnosis in neuromuscular disorders.
Keywords
Nerve Conduction Studies
ncs
NCS Pitfalls
Electrode Placement
Amplifier Settings
Stimulus Artifact
Physiological Factors
Temperature Effects
Anatomical Variants
Diagnostic Errors
Neuromuscular Disorders