Impaired afferent control in patients with spastic hemiplegia at different recovery stages: contribution to gait disorder.

The cerebral somatosensory potentials (SEP) evoked by electrical stimulation of the tibial nerve on the affected and unaffected limbs during stance and gait were recorded in 50 patients with spastic hemiplegia. On the unaffected side, the onset of the cortical activation during gait was 15 to 20ms later, and the amplitude was about 50% smaller than that recorded during stance condition. This was attributed to blocking of Ia afferent fibers during gait. SEPs recorded on the affected side during gait were, in general, of smaller amplitude and appeared with a shorter latency than in the unaffected side. During gait, 22 affected limbs showed a "Ia" blocking pattern of SEPs whereas another 28 showed a nonblocking pattern. The behavior of SEPs was analyzed with respect to three clinical identifiable recovery stages of voluntary movements in the spastic limbs (namely synergistic, isolated, and useful movements). The blocking pattern during gait was usually present in good functioning limbs, whereas the nonblocking pattern was usually present in poorly functioning limbs. It is concluded that the change in the gait pattern of hemiparetic patients represents a shift from good relevant functioning group II-afferent system to a predominance of functionally ineffective group I-afferent system.