Up to 16% of chronic inflammatory demyelinating polyneuropathy (CIDP) patients may present acutely. We performed a retrospective chart review on 30 acute inflammatory demyelinating polyneuropathy (AIDP) and 15 acute-onset CIDP (A-CIDP) patients looking for any clinical or electrophysiological parameters that might differentiate AIDP from acutely presenting CIDP. A-CIDP patients were significantly more likely to have prominent sensory signs. They were significantly less likely to have autonomic nervous system involvement, facial weakness, a preceding infectious illness, or need for mechanical ventilation. With regard to electrophysiological features, neither sural-sparing pattern, sensory ratio >1, nor the presence of A-waves was different between the two groups. This study suggests that patients presenting acutely with a demyelinating polyneuropathy and the aforementioned clinical features should be closely monitored as they may be more likely to have CIDP at follow-up.

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To determine the optimal recording site for phrenic nerve conduction studies, six different recording techniques were compared in 11 healthy volunteers (22 phrenic nerves). The mean diaphragm compound muscle action potential (CMAP) amplitude, side-to-side difference, and the number of studies with a false-positive result (CMAP amplitude <0.30 mV) were compared for each technique. The largest amplitude (0.65 +/- 0.23 mV, range 0.30-1.2 mV) with good right-left agreement (mean difference 0.15 mV) and no false positives was obtained using technique 1, where the G1 electrode was positioned 5 cm above the xiphoid process and G2 16 cm from G1 along the costal margin. This was also the easiest technique to perform. It does not require rib counting, which may be difficult and inaccurate, especially in overweight patients. At least one false positive occurred with each of the remaining five techniques.