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Published on: June 15, 2018
Variability of Sural SNAP and Peroneal CMAP Amplitudes Limits Consistent Electrodiagnosis of Chronic Axonal
Gerjan M van der Star1, Ruben P A van Eijk1, H Stephan Goedee1
1Department of Neurology and Neurosurgery, UMC Utrecht Brain Center, University Medical Center, Utrecht, the Netherlands.
Introduction/Aims:
Current consensus guidelines for the electrodiagnosis of polyneuropathy derive from highly standardized investigations performed in specialist centers, raising the question of whether they are equally applicable in everyday general neurology outpatient settings. This multicenter study evaluated the consistency of electrodiagnostic findings in chronic axonal polyneuropathy across different clinics.
Methods:
We retrospectively collected sural sensory nerve action potential (SNAP) and peroneal compound muscle action potential (CMAP) amplitude data from 62 patients with cryptogenic axonal polyneuropathy. Recordings were obtained both in general neurology outpatient clinics and in a specialized neuromuscular center in the Netherlands. After excluding technically inadequate waveforms, we assessed agreement and inter-center variability using Bland-Altman plots, standard error of measurement (SEM), intraclass correlation coefficients (ICC), relative inter-trial variation (RIV), concordance rates, and Krippendorff's α.
Results:
In quality review, 22% of sural and 2% of peroneal recordings from general neurology clinics were either reclassified or excluded because of a technically inadequate waveform. Inter-center variability was substantial for sural SNAP (ICC 0.49; RIV -200% to 200%; SEM 81%) and peroneal CMAP amplitudes (ICC 0.82; RIV -78% to 110%; SEM 37%). Agreement was poor for the classification of sural SNAP (concordance rate 69%; Krippendorff's α 0.36) and peroneal CMAP (concordance rate 73%; Krippendorff's α 0.45) as normal/abnormal, and for the electrodiagnosis of polyneuropathy (concordance rate 71%; Krippendorff's α -0.15).
Discussion:
In everyday clinical practice, substantial variability in sural SNAP and peroneal CMAP amplitudes limits consistent electrodiagnosis of polyneuropathy. Our findings underscore the necessity of rigorous quality control during nerve conduction studies.
