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.