The effects of botulinum toxin (BTX-A) on spasticity of the lower limb and on gait in cerebral palsy.

943 Spasticity in cerebral palsy stems from a net disinhibition of spinal reflexes because of a primary non-progressive cere-bral lesion. The resulting hyperactive reflexes and increased muscle tone create a dynamic, shortening deformity which is exacerbated by longitudinal skeletal growth in the growing child. This makes the management of dynamic deformities such as an equinus gait by physiotherapy and orthoses, particularly difficult during growth spurts. The objectives of management in spasticity are to opti-mise functional movement and prevent fixed deformity such as joint contracture and bony torsion. Botulinum toxin (BTX-A) has been used since the early nineties in the management of focal spasticity in cerebral palsy. 1 It is a clostrid-ial neurotoxin which achieves a reduction in tone and spasticity in a targeted muscle by temporary disruption of acetylcholine exocytosis at the motor endplate. The resulting reduction of overactivity seen in an injected muscle facilitates the function of its antagonists, allowing a change in muscle balance which may make joint movement easier. Of the seven serotypes (A-G) of botulinum toxin, sero-types A, B and F have been used in clinical practice. BTX-A has the longest duration of action, the greatest potency and is the most relevant serotype. There are significant differences between Botox the two commercially available preparations of type-A botulinum toxin, in terms of potency and therefore dosage, total protein load and antigenicity. 2 Recovery of muscle weakness after injection of BTX-A occurs in two stages. First, functional sprouts appear at the motor nerve terminal which re-establish nerve conduction. This is followed by resumption of exocytosis at the original endplate and an eventual return of the motor endplate to its preinjection state, 3 with a clinical return of spasticity at from 12 to 16 weeks in most patients. Indication The indication for the use of BTX-A injection is a dynamic spasticity, interfering with function, in the absence of fixed deformity. 4 Passive correction of the deformity should give a range of movement of a joint which will allow relatively normal gait. A failure to respond to a tone-reducing cast or an inability to gain orthotic control over the deformity strengthens this indication further. This usually follows the growth spurt at around five years of age when skeletal growth outstrips that of the resisting soft tissues. The improvement of a dynamic deviation of gait to injection of BTX-A depends on the proportion of spastic deformity to fixed deformity. In general, …