Effects of low frequency filtering on distal compound muscle action potential duration for diagnosis of CIDP: A Japanese–European multicenter prospective study

• The duration of the distal compound muscle action potential (DCMAP) largely depends on low frequency filter settings.
• The effects of low frequency filters on DCMAP duration have been systematically studied in a large number of healthy subjects and typical CIDP patients.
• We have provided the reference data of DCMAP duration using different low frequency filters, as widely available for most EMG laboratories.

ObjectiveThe duration of the distal compound muscle action potential (DCMAP) is a useful index to detect demyelination in the distal nerve segments. However in published electrodiagnostic criteria for chronic inflammatory demyelinating polyneuropathy (CIDP), the cut-off values of DCMAP duration are defined using an EMG low frequency filter of only 20 Hz. We aimed to provide widely-available reference data using several low cut filters.MethodsIn 13 Japanese and European tertiary centers, DCMAP duration data using 2, 5, 10, and 20 Hz low frequency filters were prospectively collected from 147 normal controls, 59 patients with typical CIDP, and 100 with diabetic polyneuropathy. Optimal cut-off values were calculated with receiver-operating characteristic curves, offering 100% specificity versus normal controls.ResultsThe higher low frequency filter was associated with significantly shorter DCMAP duration in all groups. For CIDP diagnosis, the calculated cut-off values had a sensitivity ranging from 51% to 66%, and a specificity versus diabetic neuropathy from 96% to 98%.ConclusionsOur results show that DCMAP duration is largely dependent on low frequency filter settings, but is a useful index for CIDP diagnosis when the cut-off values are properly determined at each filter setting.SignificanceOur data provide the systematic reference values of DCMAP duration for CIDP diagnosis available for most EMG laboratories.