Changes in voluntary motor control induced by intrathecal baclofen in patients with spasticity of different etiology.

We studied the effects of intrathecal baclofen upon voluntary movements. Eleven patients with spasticity of different etiology and one patient with idiopathic dystonia were studied. Six patients participated in a double-blind trial. Kinematic/dynamic and electromyographic (EMG) patterns were recorded during attempts at single-joint elbow or ankle voluntary movements and isometric contractions. Reflex responses were also recorded. Baclofen suppressed spastic signs in 10 patients: it eliminated clonus and decreased the co-contraction of antagonist and distant muscle groups. Baclofen could induce weakness, particularly in patients with cerebral palsy (CP). Patients with hemi-syndromes did not notice any effects of baclofen in their 'unaffected' limbs. Intrathecal baclofen could improve voluntary movements in some patients with spasticity resulting in better walking and usage of arms. We hypothesize that spasticity induces an adaptive reaction at a segmental level that includes an increase in the number and/or affinity of GABA-sensitive receptors.