Diagnostic value of satellite potentials in clinical EMG

Complex motor unit potentials (CMUPs) with satellites were recorded and analysed in 231 electromyograms of patients with spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), Duchenne muscular dystrophy (DMD) and a healthy control group. In the control adult group only few CMUPs with satellites were found; no CMUP were found in children. In SMA and DMD patients the CMUPs were present with similar frequency but their morphology, i.e. shape, duration, amplitude of the main and satellite spike components and number of satellites was different. In ALS patients a significant difference between severely involved interosseous muscle and proximal muscles was found. The pathomechanism of CMUPs with satellites is different in myopathic and neurogenic processes, in both however they reflect remodelling of the motor unit. In myopathy they reflect muscle fiber diameter variability and distribution of preserved muscle fibers within the motor unit under study. In neurogenic lesion the CMUPs with satellites are the result of increasing desynchronisation during progressive de- and reinnervation.