The effect of botulinum toxin A on gastrocnemius length: magnitude and duration of response

Thirty-nine ambulant children (22 with hemiplegia, lr with diplegia) with s pastic cerebral palsy receiving isolated gastrocnemius muscle injection wit h botulinum toxin A mere studied prospectively. The children had a mean age of 6 years (range 3 to 13 years). Measurement of gastrocnemius muscle leng th was used to estimate the dynamic component of each child's spasticity an d to quantify the response. There was a strong correlation between the dyna mic component of spasticity before injection and the corresponding magnitud e of the response after injection. Children undergoing repeated injections showed similar correlations. A strong correlation was found between the dur ation of response and the dynamic component. Children with hemiplegia showe d twice the duration for a given dynamic component compared with those with diplegia when injected with the same total dose per unit body weight. Long -term lengthening did not occur for the cohort, although some patients show ed a response at a 12-month follow-up. By delaying shortening, the injectio ns may have a role in delaying the need for surgery. Injections were well t olerated with few side effects.