NCS Perils and Pitfalls-Dr. Guo - NCS Perils and Pitfalls

Dr. Guo - NCS Perils and Pitfalls

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In this document, the author discusses the use of nerve conduction studies (NCS) to localize lesions in peripheral nerves and brachial plexopathies. When using NCS to localize lesions in peripheral nerves, the basic principle is to move along the path of a nerve at different stimulation sites to detect focal slowing or conduction block, which indicates a lesion. It is recommended to study short segments along the nerve, known as "inching," to improve detection on NCS. An example is provided of a patient with numbness in the right 4th and 5th finger, where the lesion is localized along the ulnar nerve.<br /><br />The document also covers the criteria for determining conduction block and focal slowing. A drop of over 20% in amplitude or over 50% in area from one stimulation site to another indicates conduction block. Focal slowing is identified by an abrupt drop of over 10m/s in conduction velocity. The author also highlights the perils and pitfalls of using NCS for localization, such as the inability to detect conduction block or focal slowing in cases of axonotmesis and neurotmesis due to Wallerian degeneration.<br /><br />In regards to localizing lesions in the brachial plexus, abnormal sensory nerve action potentials (SNAPs) can help differentiate between root and plexus involvement. The document provides a breakdown of the nerves associated with each segment of the brachial plexus and suggests conducting more than the usual standard sensory nerve conduction studies based on the suspected location of the lesion. Motor studies are not as helpful for localizing brachial plexus lesions, but they can aid in excluding conditions that mimic a plexopathy. The author emphasizes the importance of comparing results to the contralateral side and considering the clinical context and additional EMG information when interpreting NCS findings.<br /><br />Overall, this document provides a comprehensive overview of using NCS to localize lesions in peripheral nerves and brachial plexopathies, including the basic principles, examples, perils, and pitfalls associated with these techniques.

Keywords

nerve conduction studies

localize lesions

peripheral nerves

brachial plexopathies

focal slowing

conduction block

axonotmesis

neurotmesis

brachial plexus

sensory nerve action potentials

ncs