Electrical impedance myography correlates with standard measures of ALS severity.

Background: Electrical impedance myography (EIM) can be used to assess amyotrophic lateral sclerosis (ALS) progression. The relationship between EIM values and standard assessment measures, however, is unknown.

Methods: EIM 50 kHz phase data from 60 subjects who participated in a longitudinal natural history study of ALS were correlated with handheld dynamometry (HHD), the ALS Functional Rating Scale-Revised (ALSFRS-R) score, and motor unit number estimation (MUNE).

Results: Moderate strength correlations between EIM parameters and HHD were observed for both whole-body and individual upper and lower extremity values. Similarly, moderate strength correlations were observed between EIM and ALSFRS-R upper and lower extremity subscores, but not total ALSFRS-R scores. MUNE correlated significantly with single muscle EIM data but not with whole body or upper or lower extremity values.

Conclusions: These results support the concept that EIM can serve as a meaningful measure of disease severity in ALS.