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.

Cerebral palsy (CP) is the common diagnostic cause of the upper motor neurone (UMN) syndrome in childhood, a syndrome characterised by positive features and negative features. In CP, spasticity has both neurophysiological and musculoskeletal components. While traditional clinical evaluation of spasticity include symptoms and signs together with examination of muscle tone, range of movement (ROM), and functional impact, assessment also include validated quantitative and qualitative instruments. Oral medications affect muscles involved to varying degrees of spasticity, including both the target muscles and those for which loss of tone and/or function is undesirable. Combination treatment, such as botulinum toxin A (BoNT-A) or orthopaedic surgery, physical therapy and oral baclofen are used in clinical practice with anecdotal benefit, but the results of further scientific studies to prove the extra benefit are awaited. While selective dorsal rhizotomy (SDR) reduces spasticity, it has no effect on selective motor control (SMC), balance or fixed deformities.