Effects of intrathecal baclofen on voluntary motor control in spastic paresis.

Intrathecal baclofen injections were given to six patients with long-standing spastic paresis resistant to any nondestructive treatment, including oral baclofen. Attempts by the patients at voluntary muscle activation before intrathecal administration of baclofen led to considerable uncontrolled coactivation of antagonist and distant muscles. After the injection, dramatic suppression of the spastic signs was accompanied by more selective voluntary muscle activation. Tonic coactivation of the antagonists and distant muscle groups during voluntary contractions was decreased while the agonist level on electromyography (EMG) was not affected (three cases) or only slightly reduced (three cases). Furthermore, in one patient with sufficient residual motor control function, there was a considerable increase in the speed of fast isotonic movements, accompanied by the emergence of the ability to generate phasic muscle bursts on EMG that were characteristic of normal motor patterns. The results suggest that baclofen exerts different effects upon reflex pathways and descending motor pathways. This therapy appears to be a promising way for improving residual motor control in patients with increased muscle tone and/or reflexes.