Anterocollis may be caused by dystonic contractions of superficial and deep cervical muscles. Scalene, digastric, omohyoid muscles and platysma are supposed to be main players in anterocollis. Longus colli, longus capitis and sternocleidomastoid muscles have also been implicated in that difficult to treat form of cervical dystonia. Bilateral BoNT-A injection of sternocleidomastoids, however, is often ineffective and may be complicated by dysphagia. Therefore individual anatomical and biomechanical contributions of the anterior cervical muscles to the complex dystonic action in anterocollis need to be evaluated in detail prior to any BoNT-A injection therapy. Physiologically, the sternocleidomastoid muscles cross the coronary cervicospinal plane. Thus, in a neutral position their bilateral contraction usually leads to a retroflexion of the head and an anterior shift of the chin. By contrast, if a dystonic anterior shift is present, the trajectory of the sternocleidomastoid muscles is shifted ventrally. In this position, their bilateral contraction may contribute to an anteversion of the head. Conversely, the longus colli muscles connect the transverse processes of the cervical vertebrae with the ventral facet of the atlas, thereby exerting an anteflexion of the cervical spine and anteversion of the head independently of the sagittal head position.
We present four patients with distinct patterns of anterocollis as the main symptom of cervical dystonia. Two patients showed anterocollis with (A), two patients without anterior shift (B).
Cervical CT scan revealed asymmetric hypertrophy of longus colli muscle in (B) but not in (A). In (A), EMG-guided bilateral BoNT-A injection of the proximal and distal parts of sternocleidomastoid and anterior scalene muscles led to a significant amelioration of dystonia. In (B) repeatedly adapted BoNT-A injections of superficial cervical muscles including bilateral sternocleidomastoids, did not sufficiently improve anterocollis component, while minor torticollis components responded well. In these patients, CT-guided injection of longus colli muscles led to a sustained and functionally relevant improvement of the disabling anterocollis component.
We conclude that in anterocollis with anterior shift, sternocleidomastoid muscles should be treated bilaterally aided by EMG, whereas in anterocollis without anterior shift, CT-guided uni- or bilateral injection of hypertrophic longus colli muscle is essential for a successful treatment.
