Oculomotor functions in focal dystonias: A systematic review

Focal Dystonia (FD) is a chronic neurological disorder, which causes twisting and repetitive movements and abnormal postures induced by involuntary sustained contractions of agonist and antagonist muscles. Based on the hypothesis that several dystonia-related brain regions, including cerebellum, are implicated in oculomotor disturbances (OCD), a number of studies investigated oculomotor function in patients with dystonia. However, conceptual clarity with respect to the used assessment tools and interpretation of the findings is lacking in the literature. This is the first article to systematically review studies that assessed oculomotor function in patients with FD. In total, 329 publications, published until September 1, 2019, were identified through MEDLINE search. Twenty out of 329 studies, involving 232 subjects in total, met the inclusion criteria. Most of the studies reported oculomotor disturbances in patients with FD. Abnormalities included asymmetry in vestibulo-ocular reflex (VOR), disturbances in saccadic functions, and prolonged latencies of eye motion. Discrepancies in the results could be explained, at least partially, by the long period of time over which the reviewed studies were published, the different methods used for testing the eye movements, and the limited number of patients assessed since the majority of data derived from case reports or small-scale studies. Further prospective studies with larger subject numbers are needed, using advanced tools for the assessment of oculomotor function in focal dystonia.

Reduced vision-related quality of life in people living with dystonia

Purpose: Dystonia is a neurological movement disorder with negative impact on function and quality of life. It is currently unclear whether vision-related quality of life is affected. The aim of this study was to determine whether vision-related quality of life is reduced by dystonia.Materials and methods: A vision-related quality of life questionnaire was delivered online to probe visual function in people living with dystonia. Scores for each of six domains were compared to normative data of 819 healthy participants using one sample t-tests. Respondents were divided into two groups based on whether they had botulinum toxin injections and compared using independent samples t-tests.Results: There were 42 completed responses. There was a difference from norm for two domains; ocular symptoms (t(41) = 2.31, p = 0.026) and role performance (t(41) = 2.85, p = 0.007). There was variation in responses for all six domains. No difference in scores for the botulinum toxin injection group was found for either domain (both p > 0.74).Conclusions: Some people with dystonia experience reduced vision-related quality of life, which has potential to contribute to their disability. Health professionals should be aware of vision-related issues when managing people with dystonia and consider appropriate rehabilitative interventions to reduce disability and enhance quality of life.Implications for rehabilitationDystonia is a neurological movement disorder resulting in abnormal postures and movements.Vision-related quality of life is reduced by dystonia which may contribute to disability and reduced function.Strategies to improve vision-related quality of life should be included in rehabilitation programmes for people living with dystonia.

Is perception of visual verticality intact in patients with idiopathic cervical dystonia?

Idiopathic cervical dystonia (CD) is a focal dystonia characterized by an abnormal tilted or twisted head position. This abnormal head position could lead to a distorted perception of the visual vertical and spatial orientation. The aim of this cross-sectional study was to investigate whether the perception of the visual vertical is impaired in patients with CD. The subjective visual vertical test (SVV) was measured in 24 patients with CD and 30 controls. The SVV test is conducted in a completely darkened room. A laser bar is projected on an opposing white wall, which is deviated from the earth's gravitational vertical. Participants were seated with their head unrestrained and were instructed to position this bar vertically. The deviations in degrees (°) are corrected for the side of laterocollis in order to measure the E-effect. We found that patients were able to position the laser bar as equally close to the earth's gravitational vertical as controls (+ 0.67° SD ± 2.12 vs + 0.29° SD ± 1.08, p = 0.43). No E-effect was measured. Notwithstanding the abnormal position of the head, the perception of the visual vertical in patients with idiopathic CD is intact, possibly because of central neural compensatory mechanisms.

Postural control and the relation with cervical sensorimotor control in patients with idiopathic adult-onset cervical dystonia

Cervical dystonia (CD) is a movement disorder characterized by involuntary muscle contractions leading to an abnormal head posture or movements of the neck. Dysfunctions in somatosensory integration are present and previous data showed enlarged postural sway in stance. Postural control during quiet sitting and the correlation with cervical sensorimotor control were investigated. Postural control during quiet sitting was measured via body sway parameters in 23 patients with CD, regularly receiving botulinum toxin treatment and compared with 36 healthy controls. Amplitude and velocity of displacements of the center of pressure (CoP) were measured by two embedded force plates at 1000 Hz. Three samples of 30 s were recorded with the eyes open and closed. Disease-specific characteristics were obtained in all patients by the Tsui scale, Cervical Dystonia Impact Profile (CDIP-58) and Toronto Western Spasmodic Rating Scale (TWSTRS). Cervical sensorimotor control was assessed with an infrared Vicon system during a head repositioning task. Body sway amplitude and velocity were increased in patients with CD compared to healthy controls. CoP displacements were doubled in patients without head tremor and tripled in patients with a dystonic head tremor. Impairments in cervical sensorimotor control were correlated with larger CoP displacements (r_s ranged from 0.608 to 0.748). Postural control is impaired and correlates with dysfunction in cervical sensorimotor control in patients with CD. Treatment is currently focused on the cervical area. Further research towards the potential value of postural control exercises is recommended.

Interactions between voluntary head control and neck proprioceptive reflexes in cervical dystonia

BACKGROUND

To investigate deficiencies in mechanisms of sensorimotor processing and reflexive-voluntary interactions leading to the impaired head position control in primary cervical dystonia.

METHODS

Thirteen patients and 23 healthy controls were subjected to transient, low amplitude, low velocity head-on-trunk, trunk-under-head and whole-body rotations in the horizontal plane. With the instruction not to resist the imposed displacements, resistance to horizontal neck deflections was evaluated.

RESULTS

Patients exhibited a torque offset (bias) in the direction of torticollis before stimulus application. While controls reduced and occasionally eliminated completely the initial resistance to head-to-trunk rotations, torque in patients increased throughout displacements. Change of resistance relative to baseline in patients was, however, symmetrical, i.e. independent of torticollis direction. Spontaneous torque fluctuations were significantly larger in patients. Strong correlations existed among these abnormal findings.

CONCLUSIONS

Patients' ability to manipulate normal postural reactions to head-trunk rotations is impaired. The deficit is bilateral and correlates with the degree of abnormal posture. The present study extends previous work on reflexive-voluntary interactions and provides evidence that malfunctioning proprioceptive feedback may contribute to the pathophysiology of cervical dystonia.

The role of the trigeminal sensory nuclear complex in the pathophysiology of craniocervical dystonia

Isolated focal dystonia is a neurological disorder that manifests as repetitive involuntary spasms and/or aberrant postures of the affected body part. Craniocervical dystonia involves muscles of the eye, jaw, larynx, or neck. The pathophysiology is unclear, and effective therapies are limited. One mechanism for increased muscle activity in craniocervical dystonia is loss of inhibition involving the trigeminal sensory nuclear complex (TSNC). The TSNC is tightly integrated into functionally connected regions subserving sensorimotor control of the neck and face. It mediates both excitatory and inhibitory reflexes of the jaw, face, and neck. These reflexes are often aberrant in craniocervical dystonia, leading to our hypothesis that the TSNC may play a central role in these particular focal dystonias. In this review, we present a hypothetical extended brain network model that includes the TSNC in describing the pathophysiology of craniocervical dystonia. Our model suggests the TSNC may become hyperexcitable due to loss of tonic inhibition by functionally connected motor nuclei such as the motor cortex, basal ganglia, and cerebellum. Disordered sensory input from trigeminal nerve afferents, such as aberrant feedback from dystonic muscles, may continue to potentiate brainstem circuits subserving craniocervical muscle control. We suggest that potentiation of the TSNC may also contribute to disordered sensorimotor control of face and neck muscles via ascending and cortical descending projections. Better understanding of the role of the TSNC within the extended neural network contributing to the pathophysiology of craniocervical dystonia may facilitate the development of new therapies such as noninvasive brain stimulation.