Effects of Baclofen on Muscle Strength in Cerebral Palsy

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Cerebral palsy (CP) is the most prevalent physical disability originating in childhood of which spasticity and weakness are primary clinical signs. Spasticity management in this population has changed dramatically in the past two decades, first with the introduction of selective dorsal rhizotomy (SDR) and most recently with the introduction of intrathecal baclofen (ITB) pump implantation. ITB is efficacious for persons with spasticity of spinal origin; however, the clinical results in CP, while generally positive, are less well-established, reduction in spasticity is typically less marked, and functional gains are less impressive or even equivocal. Reported positive effects of ITB include a relaxation in spasms and spasticity which may reduce associated discomfort and improve ease of movement. A major unresolved question is whether muscle weakness is a direct effect of ITB or whether only an apparent weakness occurs due to elimination of spasticity, as seen after SDR. Exacerbation of weakness could prove problematic in these patients who are already significantly weak. The Specific Aims of this project are to:(1) quantify the changes in voluntary torque production, spasticity and selective control as a result of ITB; and (2) determine the interplay of these clinical changes on functional motor outcomes so as to improve clinical application of this therapy in CP. The following hypotheses will be tested: a) ITB will have a negative effect on isometric and eccentric peak torque production of eight (8) major lower extremity and two (2) representative upper extremity muscle groups in a dose-dependent manner; b) Isolated control of muscles opposing spastic agonists during movement tasks and gait will be conversely improved in a dose-dependent manner; c) Functional gains, including changes in gait temporal-spatial parameters and the Global Function Scale of the PODCI, will not be dose-related. Alternatively, these will depend on the individual's underlying motor capabilities, the amount of change in spasticity and strength produced by ITB, and how these changes interact to alter functional performance. Our long term goal is to improve spasticity management in CP by more precise patient selection and dosage adjustment, and greater consideration of adjunct therapies such as strength training post-operatively.