Is total duration of distal compound muscle action potential better than negative peak duration in the diagnosis of chronic inflammatory demyelinating polyneuropathy?



Introduction: The diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) is difficult, and the role of electrophysiology is crucial. Distal compound muscle action potential (CMAP) duration is a useful tool that is assessed by measuring negative peak duration (NP). The value of total distal CMAP duration (T), which seems more precise from a physiological standpoint, has not been studied. Methods: We reviewed retrospectively the records of 50 patients with CIDP and 50 controls with chronic axonal neuropathy. We constructed ROC curves for NP and T. Results: Comparison of AUC for T vs. NP showed an advantage for the former (P = 0.026 for the fibular nerve). Our derived cut-offs offered a sensitivity of 42.3% for T vs. 35.3% for NP. Conclusion: This study suggests a slight advantage for T over NP duration of the distal CMAP in the diagnosis of CIDP. However, the clinical relevance of this result must be weighed against the feasibility of this measurement. Muscle Nerve 49: 895–899, 2014