Transcranial stimulation of motor cortex in upper motor neurone syndrome: its relation to the motor deficit

The purpose of this investigation was to clarify the functional significance of the fastest cortico-motoneuronal connections in chronic upper motor neurone syndromes. Using magneto-electrical stimulation of motor cortex the intactness of cortico-motoneuronal connections was assessed in 51 patients presenting with variable degrees of impairment. There was a gross correlation between clinical impairment of the patient and the degree of pathology of cortico-motoneuronal efferents. Covariation of clinical data with transcranial stimulation was better than covariation with the size of lesion on CT scans. In some patients, however, definite clinical impairment, especially affecting distal fractionated movements, was associated with completely normal responses. There was no evidence of response abnormality in distal muscles ipsilateral to the hemispheric lesion. The data indicate that motor deficit can exist in the presence of normal cortico-motoneuronal conduction times, showing that intactness of these connections is not a sufficient condition for preservation of voluntary motor activities. This underlines the importance of other pathways for the pathogenesis of upper motor neurone syndromes.