Drilling holes through the skull to embed electrodes in areas deep within the brain that control movement may strike many as an extreme procedure but, for more than 100,000 people worldwide suffering from advanced movement disorders, this surgical treatment has been life-transforming.

Deep brain stimulation (DBS) is an adjustable, reversible and non-destructive intervention using a surgically placed medical device to deliver electrical stimulation to precisely targeted areas in the brain. Essentially, it is a pacemaker for the brain. 

A thin wire lead with four contacts (electrodes) at the tips is implanted into one or both sides of the brain, connected to a neurostimulator located near the collarbone, which is then programmed with a remote, handheld controller to block abnormal nerve signals that cause the disabling motor symptoms of Parkinson’s disease (PD), essential tremor and idiopathic dystonia. 

The procedure is most commonly recommended for patients who fail to achieve satisfactory control with medications. DBS does not replace medication but it often allows their dosage to be reduced; the combination provides better muscle and movement control than drugs alone. Research has demonstrated motor function improvements of up to 72% within a year of DBS surgery. 

DBS and Irish patients

With such marked and well-established improvements in debilitating symptoms and quality of life for these patients, a multidisciplinary expert advisory group was set up by the Health Information and Quality Authority (HIQA) in Ireland earlier this year to examine the costs, demand and clinical effectiveness associated with providing a national DBS service.

Requested by the HSE, the assessment is focusing on developing a standard for the provision of a high-quality service in Ireland, including staffing, equipment and other resources, and will evaluate the associated costs. These data will then be compared with the current practice where eligible patients are referred, under the Treatment Abroad Scheme, to centres outside of Ireland for the surgery.

Modern Medicine understands that approximately 20 to 30 patients travel from Ireland to the UK for this operation each year at a cost of £44,000 sterling, with further costs arising from travel and follow-up visits. Mr Pat O’Rourke, chairman of the Parkinson’s Association of Ireland, maintains that up to 1,200 of Ireland’s 8,000 Parkinson’s patients would benefit from DBS therapy – but only a small number are even aware of it as an option. 

“Irish patients considered suitable for DBS surgery are usually referred by the HSE to specialist centres abroad, mainly in the UK. By estimating the resources required and their associated costs, this health technology assessment (HTA) will evaluate the feasibility of establishing a national service in Ireland,” said Martin Flattery, Head of HTA Research and Planning at HIQA.

There is no timeframe yet available for publication of the assessment but it is expected that the HTA will be concluded later in the year. The completed evaluation will be submitted to the HSE and to the Minister for Health.

Prof Tim Lynch – a HSE-nominated member of the HTA group and consultant neurologist at the Mater Misericordiae University and Beaumont hospitals – was the first to propose bringing DBS therapy to Ireland and has advocated for years for public funding to establish a national service.

In 2008, following two years of planning and extensive consultation with experts in the UK, Prof Lynch and colleagues in the Mater and Beaumont hospitals succeeded in setting up the first DBS programme in Ireland at the Mater Private Hospital, in conjunction with the Dublin Neurological Institute. Later that year, the first DBS surgery was carried out on a 60-year-old man with PD at the Mater Private Hospital, which also funded the eight-hour surgery. 

“We have now established a DBS programme for Ireland and in time would hope that it would be available to all patients based on clinical need rather than ability to pay,” remarked Mr Fergus Clancy, chief executive of the Mater Private Hospital. To date, three patients have had this surgery successfully performed at the Mater Private. 

How does it work?

Careful patient selection is the most important step when considering DBS. A neurologist, on a case-by-case basis, may recommend the surgery after a rigorous pre-operative assessment. In the case of PD, for example, the best surgical candidates generally have idiopathic PD (having no specific known cause), tend to be younger, are medically refractory to therapy (wearing off, on-off fluctuations, dyskinesias, etc), and have no or mild/well-controlled cognitive dysfunction. In short, about 10-15% of Parkinson’s patients are good candidates for DBS. 

The lengthy surgery is performed by a specialised team, which includes a neurosurgeon, a neurologist and a highly trained neurophysiologist. DBS is a one or two-stage procedure under both local and general anaesthesia. The first stage begins with the attachment of a stereotactic head frame to the skull to keep the patient’s head still during surgery. 

The neurosurgeon uses special imaging techniques, such as magnetic resonance imaging (MRI) or computerised tomography (CT), to map the brain and locate the site to be stimulated. Patients are sedated for the beginning of the procedure, while the surgical team is opening the skin and drilling the opening in the skull for placement of the wire lead. The patient is awakened for placement of the electrode, so that they can give feedback regarding the sensations and side-effects they experience as the surgeon establishes the exact site for the implant. As the brain itself has no pain receptors this is not painful, although the lengthy surgery can be demanding and tiring.

Many teams worldwide also rely on the use of intra-operative microelectrode recording, which involves a small wire that monitors the activity of nerve cells in the target area, allowing them to effectively ‘listen’ to patterns of electrical activity in the brain. This helps to more specifically identify the precise brain target that will be stimulated. Once the correct target has been located, the electrode is left in place and anchored to a plastic clip that has been attached to the skull opening. The wound is then closed. In stage two of the operation, the patient receives general anaesthesia for the placement of the neurostimulator – usually under the skin near the collarbone – and the positioning of the extension – an insulated wire that is passed under the skin of the head, neck, and shoulder, connecting the electrode to the neurostimulator (or ‘battery pack’). 

It may take a few weeks until the neurostimulators and medications are adjusted sufficiently for patients receive adequate symptom relief. On average the batteries last three to five years, but will require replacement over time. Some patients turn off the system at night to extend the life of the battery. 

Overall, DBS causes very few side-effects, however, as with any surgery, the procedure is not entirely risk-free. There is approximately a 2-3% chance of brain haemorrhage that may have no significant impact, or that may cause paralysis, stroke, speech impairment or other major problems. 

A revolution in neurological treatment?

There is no doubt that DBS has developed during the past 20 years as a tremendous treatment option for several different disorders. This life-changing surgery is currently approved by the European Commission for the treatment of essential tremor, advanced PD and dystonia, as well as obsessive-compulsive disorder and more recently as an adjunctive (add-on) treatment for partial-onset seizures in adults with refractory epilepsy. The success of these procedures has led to international investigation of DBS in multiple other debilitating conditions such as depression, Tourette syndrome, addictions, autism, chronic pain and restless legs syndrome.

Research published in May indicated that DBS could offer hope for people with Alzheimer disease. The small Canadian study found that an electrode delivering low-grade electrical pulse close to the fornix – a key nerve tract in brain memory circuits – appeared to increase neuronal activity. Findings were published in the Archives of Neurology. 

Another study published in January in the Archives of General Psychiatry reported that, after two years of DBS, 92% of the 17 patients reported significant relief from their major depression or bipolar disorder and more than half were in remission, with no manic side-effects.

Though larger studies still need to be done, many researchers believe this remarkable concept – of a pacemaker for the brain – may well mark the beginning of a revolution in psychiatric and neurological treatment.