Deep brain stimulation for Parkinson's disease and other movement disorders: an evidence-based analysis.
OBJECTIVE
To determine the effectiveness and adverse effects of deep brain stimulation (DBS) in the treatment of symptoms of idiopathic Parkinson's disease, essential tremor, and primary dystonia and to do an economic analysis if evidence for effectiveness is established.


METHODS
Deep brain stimulation (DBS) is a surgical procedure indicated in the relief of motor function symptoms of Parkinson's disease, essential tremor and dystonia. It involves the surgical implantation of the DBS device, which include the implantable pulse generator or stimulator, the extension, and the lead. The electric impulse is produced within the stimulator component, and transmitted to the brain site by the extension and the lead(s). DBS surgery can be either unilateral or bilateral. The laterality of the surgery and target area for brain stimulation may vary with the type of symptom or spectrum of symptoms, and such decisions are made on a case-by-case basis. Advantages of DBS over ablative surgery is that it is comparatively less invasive, it is reversible, and it allows for stimulation of both sides of the brain. Ablative surgery, which is not practiced in Ontario, results in a non-reversible lesion and is often not conducted on both sides. Thus far, DBS has been considered as an adjunct to drug therapy.


METHODS
The standard Medical Advisory Secretariat search strategy was conducted to identify international health technology assessments and English language journal articles published from January 1, 2001 onwards. Documents were reviewed separately for Parkinson's disease, essential tremor and primary dystonia.


RESULTS
There is level 1b evidence that bilateral DBS of the subthalamic nucleus is effective in the short-term control of advanced parkinsonian symptoms, and there is level 3a evidence that the effect is sustained for at least 5 years. There is Level 3a evidence that DBS of the thalamus is effective in the control of tremor in patients with essential tremor and PD for at least 6 years. There is level 3a evidence that bilateral DBS of the globus pallidus is effective in the control of symptoms of primary dystonia for at least 1 year.


CONCLUSIONS
According to the estimates of prevalence and evidence of effectiveness, there is a shortfall in the numbers of DBS currently done in Ontario for drug-resistant PD, essential tremor, and primary dystonia.Since complication rates are lower if DBS is performed in specialized centres, the number of sites should be limited.The cost per procedure to institutions with the expertise to undertake DBS and the human resource considerations are likely to be limiting factors in the further diffusion of DBS.