Objectives: To assess changes in electrical impedance myography (EIM) parameters in amyotrophic lateral sclerosis (ALS).
Methods: Ten patients with ALS and a cohort of normal subjects underwent EIM testing of tibialis anterior. Montages using voltage and current electrodes placed at a distance (far) and in close proximity (near) were compared. The EIM parameters, resistance (R), reactance (X), and phase (theta) in the patients with ALS, were compared with normal values.
Results: theta measured at 50 kHz using the near montage was most sensitive to the presence of ALS, with 9 of 10 patients with ALS having smaller theta values than the calculated lower limit of normal. theta using the far montage and X using both the near and far montages were also sensitive to disease, whereas R did not seem to be useful.
Conclusion: EIM is sensitive to muscle abnormalities in ALS, with theta measured with near montages providing the best results.