Penn and Kroin first described the benefits reporting the treatment of six patients with severe continuing spasticity and spasms resulting from spinal injury or multiple sclerosis. Baclofen is hydrophilic and crosses the blood-brain barrier poorly. Spinal intrathecal administration bypasses the blood-brain barrier, allowing effective treatment of spasticity with a dose range that is 100 to 1000 times smaller than that required for oral treatment. The plasma levels of baclofen in patients undergoing intrathecal infusion have been found to be vanishingly low. Intrathecal baclofen (ITB) reduces spasticity, as clinically assessed using the Ashworth scale. Flexion or extension spasms, more common in the lower limbs, may occur spontaneously or in response to cutaneous stimuli in association with spasticity. The threshold of the electrically induced flexion reflex in the lower limb has been found to be reduced in spinal spasticity and the response amplitude to be increased.