Treatment of complex cervical dystonia with botulinum toxin: Involvement of deep-cervical muscles may contribute to suboptimal responses

Complex cervical dystonia is a subgroup of cervical dystonia (CD) characterised by a combination of head deviations in more than one plane. In addition to superficial neck muscles, deep-cervical muscles contribute to a broad range of neck movements. These deep muscles include prevertebral muscles for primary neck flexion, lateral vertebral muscles for shoulder elevation and head tilt and a posterior group of muscles for neck extension. The authors describe three cases of complex deviations of the neck including anterocollis, retrocollis and lateral or sagittal shifts with involvement of deep-cervical muscles, which are not easily accessible by routine botulinum toxin (BoNT) therapy. Incomplete muscle selection may be one of the causes of treatment failures with BoNT in patients with complex CD, and targeting of deep-cervical muscles should be considered when patients exhibit complex deviations involving anterocollis, retrocollis, lateral or sagittal shifts.