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Science News: Compound Muscle Action Potential Amplitude Predicts the Severity of Cubital Tunnel Syndrome

9/18/2019
 
Submitted by Elliot Bodofsky, MD
Edited by Nandita Keole, MD


Power HA, Sharma K, El-Haj M, et al, Compound Muscle Action Potential Amplitude Predicts the Severity of Cubital Tunnel Syndrome. J Bone Joint Surg Am, 2019; 101:730-38.
 

Cubital Tunnel Syndrome is the second most common peripheral nerve compression. There can be demyelination at the ulnar groove, axonal loss, or both.  The most commonly diagnostic parameter is Ulnar motor conduction velocity across the elbow. However, loss of Ulnar motor amplitude might correlate better with functional deficits (loss of grip or pinch strength). This was a retrospective study of 83 patients that underwent Cubital Tunnel surgery by a single surgeon between 2013 and 2017.  All included patients had a recent NCS at the same teaching institution, and had no other EMG/NCS diagnoses other than Cubital and Carpal Tunnel Syndrome.
 
Only the First Dorsal Interosseous motor amplitude correlated with preoperative pinch and grip strength. Neither slowing of the Ulnar motor NCV across the elbow, Abductor Digiti Minimi amplitude, nor needle EMG findings correlated with strength. The First Dorsal Interosseous motor amplitude should receive more attention in determining Cubital Tunnel Syndrome severity.      

Comments: This article looks at the electrodiagnosis of Cubital Tunnel Syndrome from a surgeon’s perspective, arguing that surgery should be performed for objective evidence of weakness. First dorsal interosseous amplitude correlates with grip and to a greater degree, pinch strength, while Ulnar motor NCV across the elbow does not. It is, however, a retrospective study and does not look at patient symptoms.  



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