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The Role Of Conduction Block In Ulnar Neuropathy At The Elbow
Kevin C. Chung, MD, MS1, Matthew M. Florczynski, MD, MS
2, Sandra L. Hearn, MD
1, Hyungjin M. Kim, ScD
1, Patricia B. Burns, MPH
1, for the SUN Study Group, MD
1;
1University of Michigan, Ann Arbor, MI, USA,
2University of Cincinnati, Cincinnati, OH, USA
Purpose: Ulnar neuropathy at the elbow (UNE) is characterized by progressive sensory and motor abnormalities. Patients with clinically evident weakness generally have advanced disease and suboptimal surgical outcomes. We aimed to better elucidate the electrophysiologic underpinnings of weakness in UNE and its association with disease severity.
Methods: We analyzed baseline electrodiagnostic tests (EDX), patient-reported outcomes and motor and sensory measurements from 177 patients enrolled in the 10-center, National Institutes of Health-funded, Surgery of the Ulnar Nerve (SUN) randomized controlled trial comparing in-situ decompression versus transposition procedures.
Results: Seventy-eight patients had normal distal compound muscle action potential (CMAP) amplitudes, 63 patients had decreased CMAP amplitudes with axonal loss (AL) only, and 36 patients had conduction block (CB) with or without AL. Compared to patients with normal CMAP amplitudes, patients with CB reported a significantly shorter duration of disease. Patients with AL only or CB had significantly decreased pinch strength. Patients with AL only had significantly decreased 2-point discrimination and Michigan Hand Outcomes Questionnaire scores.
Conclusions: Patients with CB demonstrate objective motor weakness comparable to patients with AL. Patients with AL demonstrate a longer duration of disease and worse baseline sensory and patient-reported parameters, which could reflect a more advanced or global lesion of the ulnar nerve. Patients with CB may represent an intermediate stage of disease severity with a favorable response to treatment.
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