A European multicentre reappraisal of distal compound muscle action potential duration in chronic inflammatory demyelinating polyneuropathy

Background: The electrodiagnostic value of distal compound muscle action potential duration (DCMAPD) has been studied rarely in chronic inflammatory demyelinating polyneuropathy (CIDP). Cut‐offs proposed have not been widely evaluated. The influence of low‐cut EMG filter settings ≤ 10 Hz as used in Europe is uncertain. Methods: We retrospectively reviewed records of 110 patients with typical, treatment‐responsive CIDP, from Leicester, U.K., Paris and Angers, France. All fulfilled revised European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS) clinical and electrodiagnostic criteria for typical CIDP (2010), before consideration of DCMAPD prolongation. Results were compared with those of 110 controls with chronic sensory/sensory‐motor axonal neuropathy. We constructed receiver operating characteristic (ROC) curves for each nerve and derived cut‐offs for DCMAPD prolongation, offering specificity of ≥ 98% vs. controls. Results: DCMAPD was significantly greater in all nerves for CIDP patients, compared with controls (P < 0.001). ROC curves allowed derivation of cut‐offs of sensitivities ranging from 27.1% (ulnar nerve) to 60% (tibial nerve). Using these cut‐offs to define DCMAPD prolongation in any studied motor nerve offered a sensitivity of 69.1% for CIDP and specificity of 97.3% vs. controls. Conclusion: Cut‐offs for DCMAPD are dependent on EMG filter settings. DCMAPD prolongation in any motor nerve, using our derived cut‐offs, represents a sensitive and specific marker of CIDP in patients studied with EMG equipment with low‐cut filter settings ≤ 10 Hz. Appropriate use of this parameter appears an essential criterion to consider in assessing suspected CIDP, which may be helpful in limiting extensiveness and duration of electrophysiological testing, thereby reducing patient discomfort.