Chronaxie and accommodation index in the diagnosis of muscle denervation

OBJECTIVE: To determine the sensitivity of the combined measurement of chronaxie and the accommodation index in the qualitative diagnosis of muscle denervation with needle electromyography and to compare quantitative diagnoses. DESIGN: Ninety-three neurogenic muscles diagnosed by needle electromyography were consecutively included for measurement of chronaxie and the accommodation index in this prospective study. The sensitivity of qualitative diagnosis was assessed for all muscles, separately for the acute and subacute-chronic denervation phase and for the complete and partial denervation. RESULTS: The combined measurement of chronaxie and the accommodation index showed a 90% sensitivity to needle electromyography for qualitative diagnosis of muscle denervation for all muscles. A 100% sensitivity was found for the acute denervation phase and for complete denervation. The subacute-chronic denervation phase revealed a 86% sensitivity, and partial denervation had a 88% sensitivity. The kappa coefficients did not show satisfactory agreement in quantitative diagnosis, and Bowker's test revealed a statistically significant underestimation of muscle denervation for measurement of chronaxie. CONCLUSION: The combined measurement of chronaxie and the accommodation index can be recommended for the screening of neurogenic lesions in the acute denervation phase.