The double-chin posture: Posterior sagittal shift in cervical dystonia
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.181543
Source of Support: None, Conflict of Interest: None
Idiopathic cervical dystonia is the most common form of adult-onset focal dystonia worldwide and is defined as 'involuntary twisting and turning of the neck due to abnormal involuntary muscle contractions.' Traditionally, cervical dystonia has been classified as rotatory torticollis, laterocollis, retrocollis, and anterocollis. Recently, a combination of complex cervical dystonias have been classified depending on the involvement of the movement at the neck (collis) and the head (caput). Besides these, there may also be sagittal or lateral deviation of the base of the neck from the midline. One such rare combination is the posterior sagittal shift causing the characteristic double-chin posture. This posture is characterized by anterocaput and retrocollis causing posterior sagittal shift of the head. Similarly, the patients may also have retrocaput and anterocollis causing anterior sagittal shift, resulting in a gooseneck posture. Selection of muscles for injection of botulinum toxin in such patients is difficult and requires ultrasound (US) and electromyography (EMG) guidance.
We are reporting a patient with posterior sagittal shift type of cervical dystonia having a double-chin posture. She had an excellent response following US- and EMG-guided botulinum toxin injection.
A 50-year-old female patient presented with an abnormal neck posture for 4 years, which used to get exaggerated during walking. She got some relief by holding and applying pressure with her hand over the back of her neck [Video 1]. On examination, she had a dystonic posturing of the head and neck with a double-chin appearance [Figure 1]. Her magnetic resonance imaging (MRI) of the brain and cervical spine was normal. She was injected with 220 units of onabotulinum toxin in bilateral suprahyoid, sternocleidomastoid (SCM), and longus colli muscles under US and EMG guidance. At 1-month follow-up, her cervical dystonia had improved significantly and the double-chin posture had disappeared [Video 1].
Complex cervical dystonias should be recognized and categorized accurately so that the basic defect is identified at the structural level and based on this, the proper muscle can be selected in which botulinum toxin may be injected. In 1953, Hassler described the basic dystonic movements of the neck, but newer classifications incorporated different combinations of movements, as most of the times, complex dystonias have a simultaneous blending of different movements in different planes. It was found that in patients with cervical dystonia, dystonic nodding movements, rotatory movements, and lateral flexion can originate from the occipitocervical joints or from the joints of the cervical spine. The combination of nodding movements of the occipitocervical joints with the rotatory movements of the intercervical joints can result in movements in all the three spatial planes. Camargo et al., illustrated that these dystonic movement disorders occur in a majority of the patients in two planes (50%), less commonly in one plane (approximately 35%), and rarely, in three planes (11%).
The longus colli, the posterior cervical muscles, and the levator scapulae maintain the normal position of the head, which is aligned horizontally with the cervical spine. In the double-chin posture, this alignment is disturbed by the activation of the suprahyoid muscles leading to flexion of the head on the cervical spine resulting in posterior sagittal shift. Over-contraction of the longus colli muscle causes a loss of normal lordosis of the cervical spine resulting in more flexion of the head on the cervical spine. Richel classified 78 patients with cervical dystonia patients into the neck and head types. He performed a clinical evaluation assessing the position of the neck and head in lateral tilt, rotation, and forward or backward flexion. He also performed a computerized tomography (CT) scan and magnetic resonance imaging (MRI) of the neck and classified the patients depending on the movement at the caput or the collis; however, none of the patients had a combination of anterocaput and retrocollis (double-chin posture).
In another study of 95 patients (55 female, 40 male) with established primary cervical dystonia, the authors showed that majority of the patients (78%; n = 73) experienced lateral flexion followed by rotation (61%; n = 57), forward flexion (20%; n = 19), backward flexion (15%; n = 14), and less frequently, lateral shift (9%; n = 8), and sagittal shift (5%; n = 5). They found that the most frequent form of complex cervical dystonia was lateral flexion with rotation (34%; n = 32) and the least common was posterior sagittal shift (1%; n = 1). The authors conducted this large, noninterventional study using clinical examination, CT, and MRI, with the overall aim of elucidating a more precise method of differentiating the different forms of head and neck postures in patients with cervical dystonia.
However, in a recent study by Flowers et al., 11 patients with primary dystonic anteroposterior sagittal shift as a focal cervical dystonia or as part of a craniocervical dystonia (e.g. Meige syndrome) were described prospectively. Of them, 4 patients had a double-chin posture and 7 patients, a gooseneck posture. They showed that the needle EMG recording of the cervical muscles of patients with a double-chin posture had hyperactivity in the suprahyoid muscles; this activity disappeared when patients were asked to correct the posture by moving the head forward. They performed intraoral and percutaneous longus colli muscle recording in the two most severely affected patients who had not responded to suprahyoid injection alone and found a marked increase in the resting activity in association with the double-chin posture. They treated all patients with a double-chin posture initially with bilateral suprahyoid injection, which was supplemented 3 months later by injections not only of the suprahyoid muscles but also of the SCMs and eventually, of the longus colli, if the patient benefit was <50%. With this protocol, he found the mean subjective improvement to be around 67.5% (range, 50–80%). They concluded that EMG, along with a knowledge of functional anatomy, is important in guiding the selection of muscles for botulinum toxin injection. In our group of 56 cervical dystonia patients, the patient described in this article was the only patient with a posterior sagittal shift, which again suggests the rarity of occurrence of this complex cervical dystonia in the general population.
To ocnclude, an analysis of the movement patterns of cervical dystonia to distinguish between the neck and head types of dystonia is necessary before deciding the pattern in which injections need to be administered.,
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