Ming Lai (1,3), Boubker Zaami (2), Stephan Jaiser (1,3), Ian Schofield (1,3), Mark Baker (1,3), Kevin Wilson (3), Stuart Baker (3)
1.Royal Victoria Infirmary, 2.Aston University, Birmingham, 3.Newcastle University

Introduction
In a previous presentation, we had proposed two novel metrics to describe the Poincaré plot. These were the Poincaré ratio and the “crossings” metric. The Poincaré ratio was defined as the line length of the Poincaré plot divided by the length of the spread of the Poincaré plot on the line of identity (i.e. the line representing y=x). The “crossings” metric was the number of times that the Poincaré plot crossed the line of identity. Both the Poincaré ratio and the “crossings” metric were increased in median nerves affected by demyelinating neuropathy. In addition, the Poincaré ratio and the “crossings” metric were strongly correlated to the visual impression of the “raggedness” of the compound muscle action potential.
Question
The question arises whether these Poincaré metrics provide more information than established descriptors of the CMAP, i.e. the distal motor latency and the amplitude.
Method
The relationship between the Poincaré metrics  and the distal motor latency, and the amplitude of the CMAP was examined for demyelinating neuropathy, median nerve pathology at the wrist and motor neurone disease. These relationships were compared between these three conditions. This was  achieved by comparison of fitted regression lines and by comparing the Poincaré metrics within ranges of the distal motor latency and amplitudes of the CMAP in the different conditions.
Findings
For both distal motor latency and amplitude, the relationship between both these two standard descriptors and the Poincaré plot metrics differed between demyelinating neuropathy and non-demyelinating neuropathy and motor neurone disease. For any given distal motor latency and amplitude there was a significant tendency for the Poincaré metrics to be greater in the median nerves affected by a demyelinating neuropathy. This remained true for the different strategies of analysing the data.
Conclusions:
Poincaré plot metrics are more abnormal in median nerves with a demyelinating neuropathy than in median nerves with focal pathology at the wrist relative to the distal motor latency and the amplitude, and in motor neurone disease, relative to the amplitude.
Poincaré plot metrics provide more information over and above the  distal motor latency and amplitude alone and could be analysed in conjunction with these established metrics.