Cervical dystonia: A new phenomenological classification for botulinum toxin therapy

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ABSTRACT Background Cervical dystonia (CD) is the most frequent form of focal dystonia. Over the last years botulinum toxin has been the treatment of choice, but a significant proportion of patients do not respond adequately to the preparation. It is this problem that has led to this analysis of the clinical forms of CD using additional CT and MRI examinations. Patients and Methods 78 patients were investigated whose primary CD was confirmed by the first diagnostic procedures. The position of the neck and head in lateral tilt, rotation and flexion backwards or forwards was clinically evaluated. All patients underwent CT of the soft tissues of the neck using slices at levels C1 to C7 and the bone window from the base of the skull to C7. The cervical spine and the soft tissues of the neck were examined in T1 and T2-weighted magnetic resonance imaging using a slice thickness of 2 mm, as well as in T1-weighting tilted towards the deep muscles of the neck. For comparison, the MRI data were subsequently analysed of 50 patients who did not have CD. The greatest diameter was measured and the form described of all the muscles able to be captured in the neck region, including the small neck muscles, and the positions of the cervical vertebra relative to each other were noted. Only the results of the clinical and CT bone window examinations are analysed here. Results It was found that, concerning lateral flexion and rotation, in 20% of the patients the disorder affected muscles that act on the atlanto-occipital joints (producing laterocaput and/or torticaput), and in a further 20%, only affected muscles that act on the cervical spine (producing laterocollis and/or torticollis). 60% exhibited both types of disorders, although with different degrees of head (-caput) and neck (-collis) involvement. This produced a ratio consequently for these forms of the disorder of 1:1:3. The position of C1, C2 and C3 to each other and to the base of the skull was captured in the CT bone window in angle degrees, and permitted torticollis (all 4 levels show the same angle of rotation) to be differentiated from torticaput (the base of skull and C1 levels show the same angle of rotation but at C2 and C3 this angle is different). Obviously the obliquus capitis inferior muscle has a particular role in torticaput: in 73% of the patients with CD it was clearly different on each side. Conclusions 1. It is necessary to distinguish between neck and head types (-collis and -caput) to establish the treatment strategy with Btx, since different groups of muscles are affected. 2. Visual analysis of the clinical picture is usually sufficient for differentiating dystonia involving muscles that have their origin or insertion on the cervical spine from the disorder involving muscles that have their origin or insertion on the skull. Imaging (CT bone window) is only useful in addition to clinical evaluation for assessing rotation of the head. 3. Lateral shift always occurs when there is laterocollis on one side and laterocaput on the other. A sagittal shift forwards, as a combination of anterocollis and retrocaput, is usually caused by bilateral dystonia of the sternocleidomastoid muscles. 4. Anterocollis can be differentiated from anterocaput by clinical lateral observation of the angle between the cervical spine and the thoracic spine and/or between the cervical spine and the base of the skull. The same applies to differentiating retrocollis from retrocaput. 5. The term ‘cervical dystonia’ should be understood as a generic term that encompasses both CD in the narrower meaning (where the muscles acting on the cervical spine are dystonic) and cranial dystonia (where it is the muscles acting on the skull that are dystonic). 6. If the classification of CD proposed here is taken into account, injections of Btx into muscles that are not involved in the dystonia can be avoided.