DIVERSE ABNORMALITIES OF CORTICOMOTONEURONAL PROJECTIONS IN INDIVIDUAL PATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS

Using peristimulus time histograms (PSTHs), abnormalities of composite excitatory postsynaptic potentials (EPSPs) induced by transcranial ma gnetic stimulation were studied in multiple motor units from individua ls with amyotrophic lateral sclerosis (ALS) and normal subjects. We st udied 97 motor units in the extensor digitorum communis muscle of 22 p atients with sporadic ALS and 47 motor units of 10 healthy control sub jects. Four or five motor units were studied in each patient and norma l subject. For each unit, macro motor unit potentials (Macro-MUPs) wer e simultaneously recorded from a surface electrode after spike-trigger ed averaging. The composite EPSPs in ALS showed a generally bi-directi onal deviation from the normal curve, with small EPSPs at one end, and larger amplitude EPSPs with a prolonged rise time at the other end. T he variability of EPSPs from adjacent motor units in the same individu al was significantly larger in ALS than in controls. In normal subject s there is a significant negative correlation between the amplitude of composite EPSPs and the Macro-MUPs. In ALS, the trend is reversed (po sitive) suggesting that the abnormalities of composite EPSPs are supra spinal in origin. A combination of partial attrition of the corticomot oneuronal core and hyper-excitability of surviving corticomotoneurons projecting to a given spinal motoneuron pool best explains the diversi ty of the composite EPSP in individuals with ALS. (C) 1997 Elsevier Sc ience Ireland Ltd.