Clinical application of a noninvasive multi-electrode array EMG for the recording of single motor unit activity

Using a recently developed noninvasive EMG recording technique with multi-electrode arrays we investigated the pattern and distribution of motor unit action potentials (MUAP) following maximal voluntary contraction of the musculus abductor pollicis brevis. An additional parameter, i.e. muscular conduction velocity (CV) in single motor units, was calculated from the multi-electrode array EMG recordings. From 63 healthy children of various age the normal EMG pattern and CV were derived and compared to the EMG of diagnosed patients known to suffer from Duchenne muscular dystrophy and from spinal muscular atrophy. In normal individuals the muscular CV in neonates was lowest at 1-2 m/s and gradually reached a plateau of 2.9-4 m/s from the age of 4 years onwards. The EMG in 31 children with Duchenne muscular dystrophy showed an abnormal pattern with low amplitude action potentials. In 30 out of 31 patients a significantly lower muscular CV was found. In 10 children with spinal muscular atrophy the EMG showed action potentials of abnormally large amplitude and a reduced recruitment of firing motor units. The muscular CV remained within the normal range. Compared to classical needle EMG the application of this new noninvasive EMG technique in children is painless and offers an easy-to-handle diagnostic tool to differentiate between neuromuscular diseases of denervating or of myopathic origin.