NCS Perils and Pitfalls-Dr. Narayanswami

Dr. Narayanswami - NCS Perils and Pitfalls

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This document provides a summary of a presentation on using nerve conduction studies (NCS) to characterize peripheral polyneuropathies. Peripheral neuropathy refers to a disorder of the peripheral nerves and can affect a single nerve (mononeuropathy), multiple non-contiguous nerves (mononeuropathy multiplex), or multiple contiguous nerves (polyneuropathy). Polyneuropathy can be further classified based on distribution (distal, symmetrical, length-dependent; glove and stocking; patchy, asymmetric, UE predominant, or diffuse), fibers affected (sensory, motor, sensorimotor), fiber types affected (large fiber neuropathy, small fiber neuropathy), pathophysiology (axonal or demyelinating), and time course (acute or chronic). NCS provide objective evidence of neuropathy, determine the distribution, assess the pathophysiological basis, evaluate the severity, and monitor response to treatment.<br /><br />NCS components measure the integrity of axons and myelin sheath. Abnormalities in conduction time and compound motor action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes can indicate peripheral nerve disease. Planning NCS involves assessing the history and physical exam findings, as well as considering the type of neuropathy. Specific NCS assessments are recommended for distal symmetric polyneuropathy (DSP) and non-length dependent polyneuropathy. Sural NCS is commonly used to evaluate DSP, and the sural-to-radial amplitude ratio (SRAR) can help differentiate between abnormal and normal findings.<br /><br />NCS abnormalities differ based on the pathophysiology of the neuropathy. Axonal degeneration is characterized by reduced SNAP and CMAP amplitudes, with the SNAP amplitude being more sensitive. Demyelinating neuropathies show prolonged distal latency, slowed conduction velocity, and preserved CMAP and SNAP amplitudes. Mixed neuropathies exhibit reduced CMAP and SNAP amplitudes, moderate conduction velocity slowing, and can be caused by factors such as temperature changes. Criteria for acquired and hereditary demyelination, as well as for immune-mediated neuropathies, are provided.<br /><br />It is important to be aware of pitfalls and potential confounding factors in NCS interpretation. Treatment options differ depending on the type of neuropathy, with axonal neuropathies generally lacking specific treatments, while demyelinating neuropathies can be managed with interventions such as IVIG, steroids, plasmapheresis, and immunosuppression. Understanding the criteria for different neuropathies can assist in appropriate patient management.

Keywords

nerve conduction studies

peripheral polyneuropathies

mononeuropathy

mononeuropathy multiplex

polyneuropathy

distal symmetrical polyneuropathy

glove and stocking neuropathy

large fiber neuropathy

small fiber neuropathy

axonal neuropathy

ncs