Towards early diagnosis of amyotrophic lateral sclerosis using near fibre EMG

Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of motor neurons and diagnosis is usually delayed several months. The continuous denervation and reinnervation associated with ALS are manifest in EMG signals as changes in motor unit potential (MUP) size, temporal dispersion and instability. Near Fibre EMG is a novel method to assess early changes in MUP temporal dispersion and instability using routinely recorded EMG signals in a semi-automated manner.

Near Fibre EMG values from 2318 MUs, retrospectively sampled at the time of ALS diagnosis, from 96 muscles of 15 patients were compared with values from 3954 MUs sampled from 109 muscles of 84 reference subjects.

30.1% and 46.1% of ALS MUs had MUPs with increased complexity or instability, respectively, and 17.4% had both. The potential importance and heightened sensitivity of NFEMG was highlighted when analyzing normal-sized motor units; as many as 24% of the normal-sized MUPs actually had significant instability, while 14% had increased complexity, and 7.4% had both.

Near Fibre EMG can characterize motor unit electrophysiological status and hence help quantify the degree, and course of denervation and reinnervation.

Near-Fiber EMG offers the potential to facilitate earlier ALS diagnosis, which, as promising therapies become available, can be consequential.