Checkpoint: Basic NCS and Anomalous Innervations-Session recording

Video Transcription

Video Summary

Dr. Dan Simmons, a neurologist, presents an in-depth lecture on nerve conduction studies, focusing on nerve physiology, nerve injuries, and anomalous innervations to improve understanding and troubleshooting in clinical neurophysiology. He is joined by Dr. Morgan Jordan, who introduces the basics of nerve conduction, describing axons, myelin, nerve fascicles, and how signals travel along motor and sensory nerves. They explain that axonal injuries lead to uniform amplitude reduction in nerve conduction potentials after Wallerian degeneration (taking 3-10 days), with largely normal conduction velocity and latency, though mild slowing can occur due to loss of the fastest fibers. In contrast, demyelinating injuries cause slowing of conduction velocity and prolonged latencies, localizable by comparing stimulation sites, sometimes leading to conduction block—failure of signal transmission despite intact axons at the lesion.<br /><br />They then explore anomalous innervations, particularly the common Martin-Gruber anastomosis (MGA), a median-to-ulnar motor fiber crossover in the forearm found in 15-30% of people. MGA can mimic conduction block or neuropathy patterns, so recognizing it prevents misdiagnosis. The lecture details various MGA permutations based on muscles involved, stimulation, and recording sites, explaining how to confirm MGA presence electrodiagnostically to differentiate it from pathology. Other anomalous innervations covered include the accessory peroneal nerve and the Riche-Cannieu anastomosis (ulnar-to-median motor crossover in the hand).<br /><br />The session includes clinical case discussions demonstrating application of these concepts in diagnosing and localizing neuropathies, differentiating axonal loss from demyelination, recognizing conduction block, and detecting anomalous innervation patterns. Practical points such as stimulation distances, limb temperature effects, and interpretation pitfalls are emphasized. The overall goal is fostering a deeper physiologic understanding to improve interpretation beyond rote algorithms in nerve conduction studies.

Keywords

nerve conduction studies

ncs

nerve physiology

nerve injuries

anomalous innervations

clinical neurophysiology

axonal injuries

Wallerian degeneration

demyelinating injuries

conduction velocity

conduction block

Martin-Gruber anastomosis

accessory peroneal nerve

Riche-Cannieu anastomosis