M Lai, M Baker, S Jaiser, L Vico-Pardo – Newcastle upon Tyne; C Fisher – Middlesborough; J Burge-KCL; S Catania, D Falla – NHNN; N Kane, A Oware – Bristol; A Michel- Cambridge; V Leach, A Malik – Glasgow; C Shirley- Birmingham, S Jefferson-Liverpool, G Lekwuwa-Preston, S Baker, K Wilson Newcastle University

The morphology of the Poincare plot of the rising slope of the compound muscle action potential which at times appears ragged in demyelinating neuropathy differs to that of normal. Metrics of the Poincare plot have been developed to quantify the differences. In this study a comparison between the visual assessment of the raggedness and these metrics has been made to see whether the Poincare plot metric reflects the visual impression of the raggedness. In addition the inter-rater agreement of the raggedness has been assessed.
Findings:
Fifteen experienced consultant clinical neurophysiologists assessed the compound muscle action potential acquired by stimulation of the median nerve at the wrist and the elbow of thirty-five median nerves in patients with a demyelinating neuropathy, 2 electrophysiologically normal nerves and 3 median nerves with electrophysiological evidence of median nerve pathology at the wrist. The assessment was based upon a 10 point Likert scale from no raggedness (score zero) to severe raggedness with a score of 9. The rank correlation between the score of the visual analysis and the Poincare plot metric ranged from 0.762 to 0.916. All the correlations were statistically significant.
The inter-rater agreement between the scorers as assessed by a Fleiss’ kappa was poor for each of the 10 categories of severity of raggedness with an overall agreement. However the agreement as assessed by a Kendall’s coefficient of concordance was high with a value of 0.87 (p < 0.001).
Conclusions 
These findings suggest that the Poincare metric reflects the impression of raggedness as assessed visually. This lends support that the Poincare metric is “meaningful” and further consideration could be made to uss this as a further assessment of the raggedness of the CMAP, a feature of “dispersion”.
The poor Fleiss’ kappa statistic but good Kendall’s coefficient of concordance has been interpreted as suggesting that the agreement between scorers of the absolute severity is poor, but the agreement of the rank of relative severity, ie the rank of severity is good. This may suggest that an objective value of raggedness (together with CMAP duration) may be useful in the assessment CMAP dispersion.