2024 Workshop Handout Bundle-W23RFC Unusual NCS Robinson

W23RFC Unusual NCS Robinson

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Sensory nerve conduction studies (NCS) are crucial in the electrodiagnostic evaluation of limb conditions, especially for identifying peripheral nerve lesions that affect only the sensory components. Sensory conduction studies are sensitive to pathophysiological changes and can localize injuries, making them essential for accurate diagnosis. Differences in sensory conduction parameters can pinpoint the severity and specific location of nerve injuries, such as those seen in carpal tunnel syndrome (CTS) or polyneuropathies.<br /><br />Technical factors affecting the accuracy of sensory NCS include limb temperature and the physical state of the nerves, like edema or obesity, which can distort results. Consistency in technique—whether ortho- or antidromic stimulation—is key to obtaining reliable data. Signal averaging capabilities on modern electromyographs also play a significant role in distinguishing true nerve action potentials from background noise.<br /><br />Specific nerve studies covered include the dorsal cutaneous branch of the ulnar nerve, the superficial radial nerve, the medial antebrachial cutaneous nerve, the lateral antebrachial cutaneous nerve, the posterior antebrachial cutaneous nerve, the medial and lateral plantar nerves, and the superficial peroneal nerve.<br /><br />The AANEM meeting also detailed advanced techniques for diagnosing CTS, emphasizing that electrodiagnostic tests help confirm clinical diagnoses and differentiate between CTS and other diffuse neuropathies. Techniques such as median-ulnar mixed nerve latency difference, median-radial sensory latency difference to the thumb, and others, help increase diagnostic sensitivity. These methods cross-verify results and reduce false positives.<br /><br />Specific techniques include:<br />1. <strong>Median-ulnar mixed nerve palm latency</strong> - sensitive and quantitative for diagnosing CTS.<br />2. <strong>Median-radial sensory latency difference</strong> - accuracy hinges on precise measurement setup.<br />3. <strong>Median-ulnar sensory latency difference to the ring finger</strong> - useful unless there is abnormal innervation of the ring finger.<br />4. <strong>Short Segment Sensory Stimulation across the carpal tunnel</strong> - detects focal nerve compressions within the carpal tunnel.<br />5. <strong>Composite Sensory Index (CSI)</strong> - combines several latency differences to improve diagnostic accuracy.<br />6. <strong>Median-Lumbrical to Ulnar-Interossei Latency Difference (LILD)</strong> - identifies severe cases of CTS.<br />7. <strong>Median-Thenar to Ulnar-Thenar Latency Difference</strong> - an additional technique for complex diagnostic cases.<br /><br />Through these advanced methodologies, sensory NCS can achieve higher accuracy in diagnosing CTS and other neuropathies, enhancing the clinician's ability to provide effective treatment.

Keywords

Sensory Nerve Conduction Studies

Peripheral Nerve Lesions

Carpal Tunnel Syndrome

CTS

Polyneuropathies

Electrodiagnostic Evaluation

Technical Factors

Median-Ulnar Mixed Nerve Latency

Composite Sensory Index

Short Segment Sensory Stimulation

Advanced Diagnostic Techniques

CTS

carpal tunnel syndrome