Vestibular hyperreactivity in patients with idiopathic spasmodic torticollis

The effect of cognitive task on postural stability in cervical dystonia

BACKGROUND

Cervical dystonia (CD) is the most common form of focal dystonia. It is not known exactly whether abnormal head postures in cervical dystonia cause balance problems. Dual-tasking is a common every-day life situation.

OBJECTIVE

We aimed to evaluate postural stability (PS) in patients with CD and the effect of cognitive task on PS. As a secondary aim, we evaluated the effect of onabotulinum toxin A (BoNT) injection on PS.

METHODS

A total of 24 patients with CD who were on BoNT treatment for at least one year and 23 healthy controls were included. Posturographic analyses were carried out in all the subjects on static posturography platform under four different conditions: eyes open, eyes closed, tandem stance and cognitive task. In patients, posturographic analysis was carried out just before the BoNT injections and was repeated four weeks later.

RESULTS

Before treatment, the anterior-posterior sway was significantly higher in CD patients with the eyes open condition compared to the controls (p=0.03). Cognitive task significantly affected several sway velocities. Tandem stance significantly affected many sway parameters, whereas the eyes closed condition did not. After treatment, only two parameters in tandem stance and one in cognitive task improved within the patient group, in a pairwise comparison.

CONCLUSIONS

Postural control is impaired in CD patients probably due to the impaired proprioceptive and sensorimotor integration. In reference to dual task theories possibly due to divided attention and task prioritization, cognitive dual-task and harder postural task disturbes the PS in these patients.

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.

Dystonia

This chapter presents a review of the literature for falls and abnormalities of balance and gait in isolated dystonia syndromes. Balance appears to be relatively preserved in primary and focal dystonias, except when postural abnormalities significantly displace the center of gravity of the body. Gait can be affected by abnormal dystonic movements and limb deformities, and is commonly abnormal in generalized dystonia. Impairment of gait can also be seen in patients with cervical dystonia when it results in abnormal posturing, and severe cases of blepharospasm leading to functional blindness. Gait abnormalities have also been described in dystonia associated with dopa-responsive dystonia (DRD) and Wilson disease. The data on dystonia and falls are scarce but it has been described as one of the main symptoms of DRD. Local field potential recordings point to abnormal synchronization activity in the pallidum as the main pathophysiologic finding. Cerebellar dysfunction has been reported in patients with primary dystonia and some forms of focal dystonia. While contradictory data have been published on the association between vestibular dysfunction and cervical dystonia, abnormal neck proprioception appears to be present in the latter. Treatment of the dystonia can improve balance and gait, as well as reduce the frequency of falls.

Cervical dystonia: disease profile and clinical management

Cervical dystonia, the most common focal dystonia, frequently results in cervical pain and disability as well as impairments affecting postural control. The predominant treatment for cervical dystonia is provided by physicians, and treatment can vary from pharmacological to surgical. Little literature examining more conservative approaches, such as physical therapy, exists. This article reviews the etiology and pathophysiology of the disease as well as medical and physical therapist management for people with cervical dystonia.

Secondary cervical dystonia associated with structural lesions of the central nervous system

We tested the hypothesis that structural lesions of the central nervous system (CNS) associated with cervical dystonia more commonly involve the cerebellum and its primary afferent pathways than basal ganglia structures. Cervical dystonia is the most common focal dystonia, the majority of cases are idiopathic, and only a small percentage of patients have a family history of dystonia or other movement disorders. Pathophysiological mechanisms operative in solely or predominantly appendicular dystonias such as writer's cramp and Oppenheim's dystonia, respectively, may not be directly applicable to axial dystonias. The localization of structural lesions of the CNS associated with secondary cervical dystonia may provide some insight into the neural structures potentially involved in primary cervical dystonia. The National Library of Medicine Gateway (from 1960) and a clinical database maintained by the senior author (from 1999) were searched for cases of secondary cervical dystonia associated with structural lesions of the CNS. Search terms included one or more of the following: dystonia, torticollis, cervical, secondary, and symptomatic. Lesion localization and type, patient age, patient gender, head position, occurrence of sensory tricks, and associated neurological findings were tabulated for each case. Structural lesions associated with cervical dystonia were most commonly localized to the brainstem and cerebellum. The remaining cases were equally divided between the cervical spinal cord and basal ganglia. Although inconsistent, head rotation tended to be contralateral to lesion localization. Additional neurological abnormalities were present in the majority of patients with secondary cervical dystonia. The relative paucity of basal ganglia pathology and concentration of lesions in the brainstem, cerebellum, and cervical spinal cord in patients with secondary cervical dystonia suggests that dysfunction of cerebellar afferent pathways may be important to the pathophysiology of primary cervical dystonia.

Dynamic balance function in phasic cervical dystonia following Botulinum toxin therapy

Previous research by our group revealed normal dynamic balance function in pure tonic cervical dystonia (CD) with impaired equilibrium in phasic CD patients investigated at least 3 months following Botulinum toxin (BtxA) treatment. The current study was performed to determine whether impaired dynamic equilibrium in phasic CD is influenced by symptomatic treatment with BtxA. Dynamic balance was tested in 20 patients with phasic CD on a dynamic platform with a cylindrical curved base (stabilometer) 4 weeks following BtxA treatment. Balance was assessed by the linear displacement of the platform and the maximum amplitude of platform displacement with open and closed eyes and compared with pre-BtxA data. Despite a clinically significant BtxA-induced reduction of phasic head movements, none of the platform measures improved significantly. In addition, there was no correlation between the BtxA-induced clinical improvement and changes in any of the dynamic balance measures pre- vs. post-BtxA. In conclusion, the persistent dynamic balance impairment after effective BtxA therapy may indicate that disequilibrium in phasic CD does not simply reflect disturbed vestibular input from repetitive head oscillations, but argues in favour of different sensorimotor processing in tonic and phasic CD.

Abnormal interaction between vestibular and voluntary head control in patients with spasmodic torticollis

The functional status of vestibulo-collic reflexes in the sternocleidomastoid (SCM) muscles was investigated in 24 patients with spasmodic torticollis using small, abrupt 'drops' of the head. None had been treated with botulinum toxin injections during at least 4 months preceding the study. Eight of the patients, four of whom had been studied before surgery, were also studied after selective peripheral denervation of neck muscles. The reflex was of normal latency and duration in the 'passive drop' condition, in which subjects were instructed not to oppose the fall of the head. To study voluntary interaction with the reflex response, subjects were then asked to flex the neck as quickly as possible after onset of the head drop ('active drop'). In this condition, voluntary responses in patients were delayed, smaller and less effective in counteracting the head fall than in normal subjects. The same abnormalities were also found in patients after surgery when the head posture was improved. Somatosensory/auditory voluntary reaction times in SCM were normal, as was the latency of the startle reflex. We conclude that voluntary interaction with the vestibulo-collic reflex is disrupted in patients with spasmodic torticollis, a finding which corroborates the patients' aggravation of their symptoms by head or body perturbations. Lack of effective interaction between two major systems controlling head position may contribute to torticollis.

Static and dynamic balance function in spasmodic torticollis

The consequences of abnormal head posture on static and dynamic balance skill were studied in a group of 10 patients with idiopathic spasmodic torticollis (ST). In static conditions, body sway was assessed using a conventional force platform with eyes open and with eyes closed. Standardized dynamic balance conditions were produced using a rocking platform; lateral and anteroposterior dynamic balance skills were assessed by measuring linear displacement both of the body base and of the head. Dynamic tests were repeated 6 weeks after botulinum toxin treatment in all patients. Patients' results were compared with those obtained from 10 control subjects. In static conditions, ST patients did not differ from control subjects, but in dynamic conditions, balance parameters were greater in the patient group than in the control group. This was true for the lateral direction and for dynamic balance parameters recorded both before and after botulinum toxin treatment. Eye closure significantly increased dynamic balance parameters in both groups. However, the effect of eye closure was greater in the patient group than the control group, especially for lateral sway, suggesting that patients used vision to compensate for the dynamic balance disturbance induced by the spasmodic torticollis. Despite a significant improvement of head posture in all patients after botulinum toxin treatment, no significant changes in dynamic balance parameters were observed between the first and second test. The possible origins of the dynamic balance disturbance observed in ST patients are discussed.

Vestibular hyperreactivity and hyperventilation after whiplash injury

Vestibular, oculomotor and respiratory tests were performed on 32 patients after whiplash injury caused by a rear-end car collision. Oculomotor functions were generally normal. The cervico-ocular reflex was usually absent or displayed the low gain typical of normal subjects. There was no nystagmic response to static neck torsion. The vestibulo-ocular reflex showed vestibular hyperreactivity (VH) in a significantly large number of cases (n = 17; 53%). The respiratory test results were also typical of the hyperventilation syndrome (HVS) in a significantly large number of cases (n = 12; 38%). The findings of VH and the HVS were not significantly correlated within the patient group. However, the combination of VH and the HVS occurred significantly more often (n = 7; 22%) than could be accounted for by combined false positivity. Most of the significant findings were due to high relative frequencies in the women: 11 out of the 17 women (65%) showed VH, 8 (47%) had the HVS and 5 (29%) showed a combination of VH and the HVS. The findings were not correlated with the patient's age or the time interval between the accident and the examination. VH might have been the result of plastic adaptation to limited head mobility secondary to neck pain. Behavioural and emotional distress might offer alternative explanations for both VH and the HVS.

Click-evoked vestibulocollic reflexes in torticollis

A total of 26 patients with torticollis were studied using a recently developed technique for recording vestibulocollic reflexes from the sternocleidomastoid muscles in addition to conventional caloric tests of vestibular function. Previous reports of abnormalities of vestibulo-ocular reflexes in these patients were confirmed with just fewer than half having significant canal pareses or directional preponderances (nine of 20 tested). In addition, there was a high incidence of abnormal click-evoked vestibulocollic reflexes (17 of 26 tested), which were not simply the result of prior treatment with botulinum toxin, nor due to unequal levels of muscle activation. In patients never previously treated with botulinum toxin (14 patients), the effect almost always consisted of suppressed responses in the sternocleidomastoid muscle ipsilateral to the direction of head turning. Because responses were not abnormal in all patients tested, and more commonly so in those with a history of torticollis of > or = 5 years (eight of nine patients) than in de novo patients, we suggest that the changes are more likely to be compensatory than causal.

Microvascular decompression for spasmodic torticollis

Twenty patients with spasmodic torticollis (ST) were treated by microvascular decompression (MVD) of the spinal accessory nerves, the upper cervical nerve roots and the brainstem. Thirteen were female and seven male. Median age was 47 years (range 39 to 70 years). Median duration of symptoms was 5 years (range 4 months to 17 years). Ten had right horizontal; nine, left horizontal; and one, retrocollis ST. Twenty-two operations were performed on twenty patients, suboccipital craniectomy and C1 laminectomy in 18 and retromastoid craniectomy in 4 operations. The most common compressing blood vessels were the vertebral artery and/or the posterior inferior cerebellar artery. No nerve section was performed. Three patients died of unrelated conditions, 3, 5 1/2, and 6 years postoperatively, respectively. Minimum follow-up period in the rest of the cases is 5 years (range 5 to 10 years). Thirteen (65%) were cured, four (20%) improved with minimal spasm, one (5%) improved with moderate spasm, and two (10%) improved minimally or unchanged. In most cases the cure or improvement was noticed gradually over 6 months to two years following the operation. There was no operative mortality. Postoperative morbidities included transient cerebrospinal fluid leakage through the surgical incision in one case and an apparent multiple small vessel stroke involving periventricular white matter in one reoperation case with full recovery. MVD for ST is a nondestructive benign procedure with high probability of cure or significant improvement.

Hyperactive VOR and hyperventilation after whiplash injury

Otoneurological and respiratory tests were performed on 32 patients after whiplash injury caused by a rear-end car collision. Oculomotor and cervico-ocular test results were generally normal. In a significantly large number of case, the vestibulo-ocular reflex (VOR) was hyperactive (n = 17; 53%) and the respiratory test results were typical of the hyperventilation syndrome (HVS) (n = 12; 38%). Hyperactive VOR and the HVS occurred significantly more often in combination (n = 7; 22%) than could be accounted for by combined false positivity. Most of the significant findings were due to high relative frequencies in the women. The hyperactive VOR might have been the result of plastic adaptation to limited head mobility secondary to neck pain. Behavioural and emotional distress might offer alternative explanations for both the hyperactive VOR and HVS.

Cervico-ocular function in patients with spasmodic torticollis

The cervico-ocular (COR) and active and passive vestibulo-ocular reflexes (VOR) were measured in seven patients with spasmodic torticollis (ST) and six normal controls. The COR was found to be weak or absent in both groups. The VOR gain was similar in the two groups but five patients had a significant asymmetry of the response. There was no evidence of abnormal cervico-vestibular interaction during active head rotation. The study suggests that the VOR asymmetry frequently found in ST cannot be explained on the basis of an abnormal cervical input.