METHOD: Two children (3%) received unilateral DBS for hemidystonia and were excluded and five (7%) developed
infections requiring part-DBS removal within 6 months, leaving 63 children (90%) undergoing bilateral DBS for follow-up (34 males, 29 females; mean age at surgery for the whole group 10y 4mo, SD 4y 2mo, range 1-14y). Seventeen children were classified with
primary dystonia: mean age 12 years 11 months, SD 4 years 6 months range 4 years 6 months to 17 years 3 months; 28 as having secondary-static
dystonia: mean age 10 years 2 months, SD 4 years 9 months (range 3y 3mo-20y); five as having secondary-progressive
dystonia: mean age 8 years 11 months, SD 3 years 9 months (range 5y 5mo-13y 1mo); and 13 as having NBIA
dystonia: mean age 10 years 2 months, SD 3 years 11 months (range 1-14y). Children with
primary dystonias demonstrated greater improvements in BFMDRS motor score than those in the other aetiological categories (Kruskal-Wallis test, p<0.001), which correlated negatively with
dystonia duration and more strongly still against the ratio of
dystonia duration normalized to age at surgery (DD/AS ratio) at 1 year (Spearman's rank correlation coefficient 0.4752 and -0.599 respectively). A similar significant negative correlation was found in the secondary-static
dystonia group between outcome at 1 year and DD/AS ratio (-0.461). Poorer outcome in
secondary dystonia coincided with the absence of a period of normal motor development in comparison with the
primary dystonia group. A significant improvement in BFMDRS motor score was seen in the NBIA group at 6, but not 12 months (Wilcoxon signed rank test p=0.028, p=0.85 respectively). No reduction in efficacy was seen in children with a musculoskeletal
deformity at the time of surgery.
CONCLUSION: Response to pallidal DBS in the treatment of
dystonia declines with the proportion of life lived with
dystonia in primary and
secondary dystonia. Other intrinsic factors reduce the median magnitude of reduction in
secondary dystonia after DBS. DBS should be offered early, preferably within 5 years of onset, to maximize benefits and reduce the childhood experience of
dystonia, including musculoskeletal
deformity. Other multidimensional assessments are required to understand how DBS improves the lives of children with
dystonia.