Deep brain stimulation in dystonia: The current status
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.217985
Source of Support: None, Conflict of Interest: None
Generalised dystonia can be quite devastating with significant morbidity and mortality. The medical options are not very effective and do not provide significant relief except in dopamine responsive dystonia. Botulinum toxin is useful in focal dystonia but is difficult to use in generalized dystonia. In carefully selected patients, deep brain stimulation (DBS) can significantly improve the outcome and should be considered.
In this issue, Manjunath et al., present their 6-year experience with DBS in dystonia at their center. The results reveal that most patients, especially those with primary dystonia, benefitted from DBS of bilateral globus pallidi interna (GPi). The study emphasizes that DBS is an underutilized therapy for providing benefit to these patients.
Factors influencing outcome
The response to DBS in patients with dystonia is variable depending upon the underlying etiology. Evidence is also scant regarding the role of DBS in many types of dystonias, ranging from class I evidence for primary generalized dystonias to class IV evidence for secondary and heredodegenerative dystonias.
Previous reports have suggested various factors that might influence the therapeutic response to deep brain stimulation., A younger age, less severe symptoms at surgery, and a shorter duration of disease predicted the best outcome. Patients with primary generalized dystonias, and especially those with TOR1A mutation of torsion dystonia type 1 (DYT1) gene had better response rates. Those with a longer duration of symptoms and fixed contractures did not respond well. Most of the studies were open label, but the overall improvement rates in blinded studies have ranged from 40% to 60%.
The treatment effect in secondary dystonias and dystonia plus syndromes (heredodegenerative dystonis) has not been as predictable or as good as seen in primary generalized dystonias.
Among the secondary dystonias, patients with tardive dystonia have shown the most consistent response. Patients with post-encephalitic dystonia and cerebral palsy did not benefit much from deep brain stimulation although there was improvement in the quality of life scores. Neurodegeneration with brain iron accumulation (NBIA) is the most studied form among the degenerative dystonias. However the improvement is not consistent in all the studies and has ranged from 20% to 91%, when assessed on the Burke- Fahn-Marsden dystonia rating scale (BFMDRS). The reason for less than optimal response in secondary dystonia may be the presence of other factors contributing to disability like spasticity and ataxia, which do not respond to deep brain stimulation.
Patients with focal and segmental dystonia, like those suffering from spasmodic torticollis or Meige's syndrome, also appear to respond well to DBS. While improvement in the range of 28%-70.2% (when assessed by the Toronto- Western spasmodic torticollis rating scale) was reported in primary cervical dystonia, 53%-85% improvement was noted in patients with Meige's syndrome with bilateral pallidal stimulation.,
In the study in this issue, the authors have treated 5 patients each with primary dystonia and secondary dystonia. While their overall improvement has been in the range of the figures reported previously (around 50% on the BFMDRS disability scale and the dystonia subscores at 1 year), they have not analyzed their results in the secondary dystonia group separately. It is surprising that despite inclusion of patients with secondary dystonia in the analysis, the final outcome was not influenced; their results were similar to that reported in the previous studies on primary generalized dystonia. It is important to emphasize that DBS in heredodegenerative dystonia should be performed after careful consideration and with modest expectations.
Target of DBS
The best target for DBS in dystonia is still unknown. Globus pallidus interna is the most studied target. Sub- thalamic nucleus stimulation has also shown a good response rate. In a prospective double-blind crossover study, 12 patients with dystonia had electrodes implanted in bilateral GPi and the subthalamic nucleus (STN). They were then randomized to 6 months of stimulation of either STN or GPi followed by 6 months of stimulation of the other nuclei. The results showed an equal response from stimulation of both the targets although STN –DBS was tolerated better. We also have had a similar experience [Figure 1]a and [Figure 1]b.
Battery consumption may be less with STN DBS but the occurrence of transient dyskinesia, worsening depression, weight gain and cognitive decline are the limiting factors. Other targets under exploration are various nuclei of the ventrolateral thalamus. The ventral oral anterior and ventral oral posterior nuclei have been the targets of thalamotomy for focal dystonia and in the writer's cramp. Presently, there is insignificant data on thalamic stimulation.,
Duration of benefit
Few studies exist that report on the long-term benefits of DBS on dystonia but in these, the response persisted for 7 to 10 years. Battery replacement may be required at 2-4 years as the energy consumption rates are high. This phenomenon has also been seen with a patient in the current study.
This study is noteworthy as it is the first study reporting the results of DBS in dystonia from India with good results. This should prompt clinicians to consider DBS in medically refractory primary generalized dystonia.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.