Dispersion of the distal compound muscle action potential as a diagnostic criterion for chronic inflammatory demyelinating polyneuropathy

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Abstract
Objective: To assess distal compound muscle action potential (DCMAP) duration as a diagnostic criterion for chronic inflammatory demyelinating polyneuropathy (CIDP). Background: Current electrodiagnostic criteria for CIDP have high specificity but limited sensitivity. Prolonged DCMAP duration has been reported in acute inflammatory demyelinating polyneuropathy. The authors have compared DCMAP duration in patients with CIDP, diabetic polyneuropathy (DP), ALS, and musculoskeletal pain syndrome (MSP) to determine whether it enhances the sensitivity of electrodiagnostic criteria for CIDP. Methods: Data from 23 CIDP, 34 DP, 34 ALS, and 54 MSP patients were reviewed. The time interval between onset of the first negative peak and return to baseline of the last negative peak of the DCMAP was calculated for each nerve. To distinguish CIDP from DP, ALS, and MSP, optimal cutoff values for DCMAP duration were achieved with receiver-operating characteristic curves. The sensitivity and specificity of these cutoff values were compared with each of four sets of electrodiagnostic criteria for CIDP. Results: Mean DCMAP duration in CIDP was significantly longer than in DP, ALS, and MSP. The sensitivity of existing electrodiagnostic criteria for CIDP ranged between 0.43 and 0.61. Their specificity vs DP or ALS was 0.91 to 1. Using DCMAP duration of ≥9 milliseconds for any of four motor nerves yielded a sensitivity of 0.78 for CIDP and specificity of 0.94 vs DP or ALS. Adding DCMAP duration criteria to any one of the three accepted criteria enhanced their sensitivity with little sacrifice of specificity. Conclusion: Quantitation of DCMAP dispersion shows promise as a sensitive and specific adjunctive electrodiagnostic criterion for CIDP.