Refining Electrophysiological Criteria in CIDP and MMN : Toward a Unified Definition of Motor Conduction Block and Proximal Temporal Dispersion

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BACKGROUND: The definition of motor conduction block (CB) and proximal temporal dispersion (TD) for the diagnosis of CIDP and MMN remains debated, particularly regarding whether CB should be based on amplitude or area reduction, and whether proximal TD is best assessed using negative peak or total CMAP duration. METHODS: Nerve conduction waveforms from 106 CIDP, 87 MMN, and 234 controls were analyzed. Motor CB was defined by ≥ 30%, ≥ 40%, or ≥ 50% amplitude or area reduction. Proximal TD was defined as a ≥ 30% increase in negative peak duration, total CMAP duration, or either criterion. Sensitivity, specificity, and inter-rater reliability were analyzed. RESULTS: Across both CIDP and MMN, a ≥ 30% reduction in CMAP amplitude showed diagnostic performance comparable to area-based CB definitions and outperformed higher cutoff values. Requiring CB in multiple nerves increased specificity but reduced sensitivity. For proximal TD, negative peak duration was the most robust single parameter. Total CMAP duration identified additional abnormalities and, when combined with negative peak duration, improved diagnostic sensitivity in both disorders while maintaining high specificity. Total CMAP duration demonstrated good inter-rater agreement at the patient level. CMAP morphology showed substantial overlap between CIDP and MMN and limited discriminatory value. CONCLUSIONS: A ≥ 30% reduction in CMAP amplitude can be used as a universal definition of motor CB in both CIDP and MMN, providing diagnostic performance comparable to area-based criteria with greater simplicity. In addition, proximal TD assessed using total CMAP duration may represent a complementary electrophysiological criterion in both disorders.

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