Clinical aspects of DBS

Deep brain stimulation is a neuro-surgical technique where a 'pacemaker', originally modelled on the cardiac pacemaker, is implanted to apply electrical pulses to a deep, subcortical brain region. This is primarily being used for movement disorders such as Parkinson's, essential tremor, multiple sclerosis and dystonia, though other uses are emerging. When placed in areas of the thalamus or basal ganglia, a high frequency stimulation can relieve dyskinetic symptoms. It is a relatively recent addition to the clinician's arsenal, and is slowly gathering momentum as an acceptable, safe and efficious intervention.

Such techniques are only available for severe, refractory disorders. The use of such major surgery in controlling a disease is usually the last line of treament. Due to the intesive work required by a team of surgeons, neurologists and radiographers, such operations are costly and avoided if possible. There is a risk to the patient, who is likely to be in a bad state anyway, and who may not even benefit from the surgery. Brain haemorrhages occur in every few patients, and adverse reactions to implants also arise. Thus only patients in dire circumstances are elegible for DBS.

DBS for Parkinson's Disease

The efficacy of DBS in movement disorders has been generally accepted, and is clear to see - press on, and the tremor stops. When comparing test scores for 'activities of daily living' there is usually a distinct improvement for patients, starting immediately and lasting for years. The need for L-Dopa, the standard drug therapy for Parkinson's, is also reduced.

The patient's wellbeing is often overlooked, as it is an inherently chaotic variable, but still crucial when considering how appropriate DBS is in treating Parkinson's. Improvements in the quality of life of patients has been addressed by very few studies. Results in those few are still promising, showing general improvements, which likely originate from the ability to better perform daily tasks and live independently. [Diamond & Jankovic,2005]

When treating Parkinson's the sub-thalamic nucleus is the current preferred site for DBS, although the internal globus pallidus and the ventromedial nucleus of the thalamus are also effective. Each has its own distinct benefits, however there is no direct comparitive work assessing stimulation of these different areas. [Patel et al,2003]

Targets for DBS in treating movement disorders-

Thalamus: tremor
Globus pallidus: rigidity, bradykinesia, dyskinesia, dystonia
Subthalamic Nucleus: rigidity, bradykinesia, dyskinesia, tremor postural instability

DBS in the subthalamic nucleus has some curious side-effects, including an impaired ability to interpret certain facially expressed emotional cues. Naturally this will have an impact on the patient's social life. Other chronic changes may occur, and their prevalance should be weighed up against benefits of the treatment, requiring further studies into the effects of DBS in the many sites it is applied to.
[Dujardin et al, 2004]

Applying DBS to other disorders

DBS has been applied to severe cases of migraine and cluster headaches, obsessive-compulsive disorder, epilepsy and neuropathic pain of specific origin.
[Schlaepfer,2005]

Cluster headache can be a devastating affliction in those who don't respond to drug therapies. DBS to the ipsilateral ventroposterior hypothalamus has been shown to dramatically reduce symptoms in patients with otherwise refractory cluster headaches. In some, repeated adjustments to the stimulation parameters over several months were needed to obtain relief. In addition after 1 month of stimulation, nitroglycerin, a classical trigger for attacks, was unable to provoke an attack in patients for whom DBS had relieved their symptoms.. This suggests that the hypothalamic stimulation had induced remission.

The best target for effective DBS in cluster headache remains to be determined. Activation of various central
structures belonging to the pain network was reported, which could be in line with the observations of general analgesia observed after hypothalamic stimulation in animals and humans. However it is likely that other actions contribute to the overall effect, as shown by the ineffectiveness of nitroglycerin after prolonged treatment.
[Schoenen et al,2005]