Dystonia

INDEX

 

Cervical dystonia is a form of focal dystonia in the neck muscles, and is also called torticollis.
A wide variety of abnormal positions of the head and neck can be present, and there is often a mixed picture.  Cervical muscles have a redundant organization
Each head and neck movement can be generated by more than one muscle or muscle combinations. Phenomenology alsone is frequently insufficient to determine injection site.

  1. Rotation if the chin is turned to the left or right
  2. Laterocollis the ear is moved towards the shoulder.
  3. With an antecollis there is forward flexion of the head, that is, the chin is moved towards the chest. At one
  4. Retrocollis there is a backward position of the head, with the head in the neck
  5. High riding shoulder
  6. Combination type:  this is commonly a combination of extension, rotation and tilt1.

Muscle Selection

About a third of patients with cervical dystonia are reported to have a poor response. In part, the reason for this may be an oversimplistic approach, limited to the forms of dystonia associated with the superficial muscles of the neck. Superficial muscles (Splenius, Sternocleidomastoid, Trapezius) are easy to inject but are not universally responsible for the abnormalities of head posture. Certain patients may have dystonia of deep muscles, such as obliquus capitis inferior (OCI), longissimus capitis, and the scalene muscles. There are multiple neck muscles with overlapping functions, which may generate the same movement, although different combinations of muscles are involved. The commonest reason for failure of botulinum toxin treatment is that the correct muscles have not been identified, or that accurate injection of a desired muscle has not been achieved.

A critical question in cervical dystonia is the site of action of the dystonic muscles: primarily related to muscle attachment to the skull, or to the neck. As an example, the sternocleidomastoid muscle, inserted on the mastoid process, is only able to act on the head, and the semispinalis cervicis muscle, inserted on the cervico-thoracic spine, can only exercise action on the neck. Distinguishing between caput and collis has improved results as measured by the TWSTRS2.

The C2/C3 vertebra can be regarded as a fixed point.  This is related to the numerous muscles which insert at the spinous process of C2 (obliquus capitis inferior, rectus capitis major, semispinalis cervicis, multifidus)3.

Figure 1. Deep posterior neck muscles


Computed tomography has shown that approximately half of the neck rotation occurs at the C1-C2 (atlanto-axial) level, centred around the odontoid process. Following that, the midcervical region shows the greatest amount of rotation (approximately 5 degrees) and the C7-T1 segment the least.  There is virtually no rotation occurring between occiput and atlas: the ellipsoid form of the atlanto-axial joints allows for flexion-extension, and to a lesser extent, for lateroflexion4.

Atlas and Axis

There are therefore two groups, caput (head) and collis (neck):

 

Muscles may also be divided on the basis of their function, and relationship to how the abnormal head posture is produced:

Figure 2.  Example of compensatory muscle limiting the degree of laterocollis.


Example of shoulder elevation affecting lateroflexion; when the shoulder elevation on the left is corrected, a laterocollis to the left is revealed

From:  Reichel G. Cervical dystonia: A new phenomenological classification for botulinum toxin therapy. Basal Ganglia 2011; 1: 5–12.

Figure 3.  Anatomy underlying the col-cap concept, and showing the important structures of the posterior triangle of the neck.

 

Note that the col-cap approach is used for dystonic postures, but not for the fast or jerky component that contributes to dystonic movements.

  Example of right lateroflexion:

  1. Right paravertebral muscles (splenius, semispinalis) are dystonic.

  2. Left trapezius is antagonistic, passively tensed by abnormal movement.

  3. Right Levator scapulae is compensatory.

 

 

From: Tatu L, Jost WH. Anatomy and cervical dystonia: “Dysfunction follows form”. J Neural Transm 2017; 124: 237–43.

Historical aspects for muscle selection

Examination features for muscle selection:

Ideally the patient is seated parallel to the observer on a chair without a backrest

Inspection

Palpation

  • Dystonic postures (slow postural component)
  • Dystonic movements (fast, jerky component)
  • Muscle hypertrophy
  • Muscle hypertrophy
  • Passive range of motion
  • Evoked pain
  • Deep muscles are not accessible, whereas superficial layers may be both inspected and palpated, and muscles in the intermedite layer may be palpated.
Examination protocol
  1. Standing at rest: Eyes open and shut (eyes closed to remove visuospatial integration which can lead to compensation and correction of position)
  2. Standing with arms oustretched in different directions
  3. Walking normally (as a distracting manouevre)
  4. Walking with arms outstretched (as a distracting manouevre)
  5. Sitting at rest, also with eyes closed
  6. Allowing movements to occur without opposition: this helps to distinguish the primary abnormal posture due to dystonia from compensatory postures and movements.
  7. Fixation of shoulder if shoulder elevated (requires additional examiner)
  8. Use of sensory tricks
  9. Consider adding examination of postures while patient is writing PMID32285434 

Inspection:

EMG

EMG is useful for identifying muscles which are dystonic, and for ensuring that the toxin is delivered to the correct muscle. An important issue is that abnormal neck positions may be caused by different combinations of dystonic activity, and that this may only be resolved with EMG. A particular issue with use of EMG is the difficulty of distinguishing a dystonic muscle from one which is compensatory.

Alternative approaches might be to use ultrasound or MRI to assess muscle hypertrophy.

- Use of a Rating Scale may be of value.

- Videotaping may be of value for comparison subsequently with the initial presentation.

Major Side Effects

Note that adverse events decline after initial treatment sessions7,8.  It appears likely that the degree of spread from the site of injection to adjacent muscles may vary depending on the product used.

  1. Swallowing difficulties. It is agreed that the highest risk of swallowing difficult arises from injection of the lower third of the sternocleidomastoid muscle, especially if bilateral.
  2. Weakness of neck extensors is also a common side effect, typically associated with injections of semispinalis capitis.
     
 
Table 1. Forms of cervical dystonia

 

From: Reichel G. Dystonias of the Neck: Clinico-Radiologic Correlations. In: Dystonia - The Many Facets. InTech, 2012. DOI:10.5772/27896.

 

Figure 4. The four groups of collis and caput conditions

 

Note relationship of surface markings:

1. Sternal notch and Larynx: deviated from one another in the case of torticollis, but not torticaput.

2. The relationship of the external auditory meatus to the clavicle. In the case of ante- and retrocollis, the meatus is displaced anteriorly or posteriorly. In the case of caput conditions, the meatus lies over the clavicle.

From: Tatu L, Jost WH. Anatomy and cervical dystonia: “Dysfunction follows form”. J Neural Transm 2017; 124: 237–43.

Figure 4. Motor phenomenology

The spectrum of involuntary movements or abnormal postures of the head and neck is very varied with respect to speed, amplitude, rhythmicity, duration and direction of movements. Smaller amplitude, higher frequency movements may be superimposed on the large amplitude movements. These may be horizontal, vertical or mixed tremulous oscillations.
Patients may have:

 

 

Phenomenology Posture dominant subtype: few dystonic movements (which mainly occur with voluntary head repositioning) Tremor Dominant subtype 

(vv)MDS3.mp4(tt)
Head rotation: towards the right, mild tilt to the left

Dystonic Postures: present

Dystonic Movements: none

Active Range of Head Motion: to left and right

Pain: none

Left Sternocleidomastoid: hypertrophic and hyperactive

Head movements with eyes open and closed

Reduced attempts to compensate head/neck alignment based on environmental landmarks

(vv)MDS4.mp4(tt)
Prevalent phenotype:Tremulous, mainly NO-NO phenotype; jerky component varying in frequency and direction

Dystonic Postures: A sagittal shift with mild retrocollis

Dystonic Movements: Variable head tremor:

                                  At rest with open eyes

                                  Disappearing with closed eyes

                                  Attenuating during head rotation to either side

                                  Increasing with walking or raising arms

Active Range of Head Motion: limited bilaterally

Muscle Selection
  • Head Rotation: left sternocleidomastoid, right splenius, right Obliquus Capitis Inferior (OCI)
  • Lateral tilt: left levator scapulae
  • NO-NO Tremor: Left and right splenius and left and right Obliquus Capitis Inferior (OCI)
  • Round and Round Tremor: Left and right levator scapulae muscles; particularly if their palpation causes pain.
Phenomenology Mobile Postural subtype Jerky and Postural Subtype: evenly weighted degree of postures and movements

(vv)MDS1.mp4(tt)
Prevalent phenotype: a variety of mobile postures (slow or fast), with some tremor.

Dystonic Postures: Left head rotation and right head tilt

Dystonic Movements: Occasional left head tilt and left shoulder elevation (requires verification by instrumented assessment)

Raising arms or walking activating abnormal postures and movements

Head Range of Motion: Limited, particularly to the right.

(vv)MDS2.mp4(tt)
Prevalent phenotype: Segmental dystonia with cranial and cervical involvement.

Dystonic Movements: Predominantly jerks at rest with eyes closed and when attempting to turn her head to the right

Diminishing jerky movements and predominant postures with complete head rotation to the right

Muscle Selection
  • Mobile Dystonia: left splenius, right sternocleidomastoid, left levator scapulae, left posterior scalene, and right trapezius (superior branch)
  • Tremulous Component: longissimus capitis, bilaterally
  • Right sternocleidomastoid, left splenius, left levator scapulae, and left obliquus Capitis Inferior (OCI)

 

 

Figure 4. Important anatomical structures

A. The posterior triangle of the neck is delineated by the posterior edge of the sternocleidomastoid muscle and the anterior edge of the trapezius muscle. The base of the triangle is the middle third of the clavicula, and the apex of the triangle, behind the mastoid process, is a narrow area where sternocleidomastoid and trapezius muscles meet.

The following muscles are found in the triangle:

Synergy of action is found in the following, due to identical muscle fibre orientation:

 Sternocleidomastoid + Trapezius

 Splenius + Levator scapulae

B. The important flexor muscles of the neck (longus colli and longus capitis) are shown.

A B

 

Insertions of important cervical muscles: skull base and cross sections at C2, C5 and C7 levels

 

Suboccipital deep uscles (within triangle) lie deep to splenius capitis, and are mainly responsible for extension and rotation. 
The anterior deep muscles flex the neck and head.

Dystoni


ANTERIOR

Longus capitis

Longus colli
 


LATERAL 

SCM

Levator scapulae

Scalenus anterior

Scalenus medius

Scalenus posterior
 


POSTERIOR

Superficial

Trapezius

Intermediate

Splenius capitis

Splenius cervicis

Deep

Obliquus capitis inferior

Rectus capitis major

Longissimus capitis

Semispinalis cervicis

Semispinalis capitis


 

 

References

1             Marion MH, Humberstone M, Grunewald R, Wimalaratna S. British neurotoxin network recommendations for managing cervical dystonia in patients with a poor response to botulinum toxin. Pract Neurol 2016; 16: 288–95.

2            Jost WH. Torticaput versus torticollis: Clinical effects with modified classification and muscle selection. Tremor and Other Hyperkinetic Movements 2019; 9: 1–4.

3            Tatu L, Jost WH. Anatomy and cervical dystonia: “Dysfunction follows form”. J Neural Transm 2017; 124: 237–43.

4            Penning L, Wilmink JT. Rotation of the cervical spine: A CT study in normal subjects. Spine (Phila. Pa. 1976). 1987; 12: 732–8.

5            Reichel G. Dystonias of the Neck: Clinico-Radiologic Correlations. In: Dystonia - The Many Facets. InTech, 2012. DOI:10.5772/27896.

6            Castagna A, Albanese A. Management of cervical dystonia with botulinum neurotoxins and EMG/ultrasound guidance. Neurol Clin Pract 2019; 9: 64–73.

7            Brin MF, Comella CL, Jankovic J, et al. Long-term treatment with botulinum toxin type A in cervical dystonia has low immunogenicity by mouse protection assay. Mov Disord 2008; 23: 1353–60.

8            Jinnah HA, Comella CL, Perlmutter J, Lungu C, Hallett M. Longitudinal studies of botulinum toxin in cervical dystonia: Why do patients discontinue therapy? Toxicon 2018; 147: 89–95.

9              Reichel G. Cervical dystonia: A new phenomenological classification for botulinum toxin therapy. Basal Ganglia 2011; 1: 5–12.