Longitudinal study of central motor conduction time following stroke. 1. Natural history of central motor conduction.

A 12 month longitudinal study has been performed on 118 subjects following first-ever stroke to determine changes in central motor conduction time (CMCT) to upper limb muscles. The responses to electromagnetic stimulation of the motor cortex and cervical motor roots were recorded bilaterally in the surface electromyograms of pectoralis major, biceps and triceps brachii and thenar muscles. The CMCTs obtained from these recordings in stroke patients have been compared with those obtained in 53 normal healthy subjects of a similar age. The first measurements were made within the immediate post-stroke period (12-72 h of the onset of symptoms) and repeated at set time intervals over 12 months. The first assessment of CMCT identified three groups: those with normal responses, delayed responses and absent responses. During the first 12 months following stroke various changes in CMCT occurred. Central motor conduction time may remain unchanged, delayed CMCT may return to normal and previously absent responses may reappear and be delayed or normal. Using electromagnetic stimulation of the motor cortex the thresholds for motor evoked responses in the different muscles were initially high and fell over 12 months.