Spontaneously changing muscular activation pattern in patients with cervical dystonia

The objective of this study was to determine stability of the neck muscle a ctivation pattern in a given dystonic head position in patients with cervic al dystonia (CD). We assessed 26 patients with CD and botulinum toxin (BT) treatment failure before surgical denervation. None of them had received BT injections for at least 4 months. To relate dystonic head position to unde rlying neck muscle activity, we used synchronised video and poly-electromyo graphic (EMG) recording over a period of 10 minutes. The muscle activation pattern during constant ("stable") maximal dystonic excursions was analysed . EMG data of nine patients was excluded from the analysis, as these patien ts had a constantly changing head position or marked head tremor. In the re maining 17 patients, who had a fairly stable dystonic position, muscular ac tivation patterns during the recording spontaneously changed in nine (Group A) while in eight it remained stable (Group B). There was no significant d ifference in demographic variables between the two groups other than a male predominance in Group A. However, the retrospectively determined initial r esponse to BT treatment (before BT treatment failure had occurred) was sign ificantly worse in Group A as compared with Group B. Neck muscle activation patterns can spontaneously change in CD patients despite constant dystonic head position, implying an inherent variability of the underlying central motor program in some patients. This should be considered when BT treatment response is unsatisfactory, and should also be taken into account when int erpreting results of EMG recordings of neck muscles in these patients. (C) 2001 Movement Disorder Society.