Intrathecal baclofen, or baclofen delivered directly into the CSF, has been found to be of use in the treatment of both limb spasticity and limb spasms.
Spasticity is defined the tightening of muscles in response to their movement. A feature of this condition is a progressive tightening in the muscle (and thus an increasing resistance to its movement) in response to repetitive stretching of the muscle. A simple example is the progressive loss in range of movement and ease of movement in a leg that is repetitively bent and then straightened at the knee. This phenomenon is amplified when the velocity of the movement or stretching is increased.
Spasms are involuntary tightening of muscles or muscle groups. They typically occur either randomly or in response to some environmental stimulus such as a loud noise. They can occur during sleep and are commonly painful.
Intrathecal baclofen is also under investigation for the treatment of other forms of muscle hypertonia (increased tone in a muscle), as seen in children with cerebral palsy (e.g., dystonic cerebral palsy). These uses are not currently approved by the Food and Drug Administration (FDA) unless as a part of an authorized investigation. Consequently, if the drug is to be used intrathecally for these other forms of hypertonia, it must either be off label (use not indicated by manufacturer or government) or part of an approved, experimental study. This should not be as risky as it sounds at first blush because the drug's use in children has been investigated and the potential side effects and complications are well known. What may not be as well known is the potential for the drug's use to result in the desired outcome in these situations.
Most centers using this treatment favor its use when a more permanent treatment is not indicated, because of either risk to limb function or an inability to tolerate a major operation. In some centers it is also employed to treat children with mixed cerebral palsy (several forms of hypertonia are present). Not uncommonly, if a child is felt to be a candidate for intrathecal baclofen, a drug trial is carried out. A dose of the drug is injected into the CSF space in the lower back via a spinal tap, and the effect on the hypertonia in the legs is then evaluated over the remainder of the day. If a desirable diminution in the leg tone occurs without undesirable side effects, the child is felt to be a candidate for implantation of a pump for the chronic delivery of the drug. If the injection is ineffective in dealing with the leg hypertonia, a higher dose of the medication may be tried on a different day.