Medical treatment for the effects of cerebral palsy
Spasticity is a major issue for the majority of children with cerebral palsy. In a population-based cohort of children with bilateral CP, 89% had signs of spasticity in their legs. A number of medical treatments are now available for treating spasticity, each with varying degrees of success:
- motor point injections including phenol, alcohol and botulinum toxin
- intrathecal baclofen
- oral medications, including baclofen, dantrolene and diazepam
The past few years has seen major advances in the medications available for treating muscle spasticity in children and adults with cerebral palsy. In particular, botulinum toxin can be given intramuscularly into spastic muscles at 4-6 monthly intervals. It prevents the release of acetylcholine from vesicles at the motor end plate and thereby chemically denervates the muscle temporarily until new nerve end terminals are sprouted. The effect of botulinum toxin on muscle tone usually lasts 3-4 months.
The short term action of the toxin is to reduce spasticity but at the same time it may increase weakness. It is possible that treatment with botulinum toxin may prevent the development of contractures and delay the need for corrective surgery.
There appears to be a dose dependent effect, but this needs further research. The toxin is most effective in dynamic spasticity rather than muscles with fixed contractures. Therefore, better results are achieved in young children who, in addition, can re-learn gait patterns more easily and have a greater carry over effect when the spasticity has recurred. The effect of botulinum toxin can be variable and it is essential to observe the results closely in each child, particularly with gait analysis where appropriate.
Most clinicians do not exceed 30-35 units per kilogram of body weight of botulinum toxin type A ('Dysport') at one session, to avoid generalised muscle weakness. (Two types of botulinum toxin A are commercially available - Dysport and BoTox. Potency differences make it important to maintain continuity for patients. Typically 1 unit of BoTox is equivalent to 3-4 units of Dysport).
This is divided between as few muscle groups as possible in the lower limb (1-2 each side), although more muscle groups may be injected in the smaller muscles of the upper limb.
This can be done in an outpatient setting under local anaesthetic with the use of topical anaesthetic creams. Midazolam 0.5mg/kg can be given orally 20 minutes before injection. Several injections into each muscle are optimal and higher concentrations with lower volume are less painful.
Electromyography is useful to locate some muscles, especially in the upper limb. General anaesthesia may occasionally be needed for deep muscles such as tibialis posterior in some children. It has been suggested that electrical stimulation of the injected muscle for periods afterwards may enhance the effect, but this can be painful.
There is the possibility of drug resistance with long-term usage of botulinum toxin in large doses in CP; this has been observed in some adults treated for torticollis. It is known that antibodies can be formed against botulinum toxin, but their significance is unknown. It has been suggested that injections should not be given less than 9 weeks apart to avoid the possibility of resistance developing.
Use with physiotherapy
Passive stretching of muscle becomes much easier after botulinum toxin treatment. For maximal effect additional physiotherapy should be given in the period following injections.
Evaluating the effect of botulinum toxin is essential to define its place in the management of CP. Research is needed into all aspects of this treatment, with careful evaluation of the results. Laboratory gait analysis, the Gross Motor Function Measure, joint range of motion at rest and functional scales are useful outcome measures.
It is hoped that botulinum toxin will be an effective treatment for spasticity when started in the young infant, maintaining mobility and function. Orthopaedic surgery can then be considered around the age of seven years or even later.
Baclofen is a GABA-agonist acting on spinal nerve synapses and reducing spasticity. It crosses the blood brain barrier poorly and this limits its use orally.
It can be given as a continuous infusion into the spinal theca through a catheter connected to a pump located in a subcutaneous pouch in the abdomen. The spasticity in the lower limbs can be significantly reduced in this way, with some effect also in the upper limbs.
There are a number of problems associated with this technique, including infection, catheter problems and CSF leakage, and the children need close monitoring by an experienced team.
It is also expensive, costing four times the amount for selective dorsal rhizotomy in the first year. It could find major usage in severely disabled individuals in whom spasticity reduction may improve nursing care.
This is a good antispastic agent for use post-operatively and in severely physically impaired people. However, its sedative effects limit its use.