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DEEP BRAIN STIMULATION IN PARKINSON''S DISEASE¹
Parkinson's disease is a degenerative neurological disorder that primarily affects the dopamine neurones of the locus niger characterised by rest tremor, bradykinesia and rigidity. The estimated number of patients in France is approximately 100,000. This disease has major social and economic implications; the medical costs it entails are estimated to be in the region of the € 472 million per year.
The limitations of levodopa therapy have led to a renewed interest in the surgical approach to treating the disease. DBS involves a stereotactic neurosurgical operation during which an electrode is placed in the deep brain structures, often on both sides, and preferentially in the subthalamic nuclei. These electrodes are connected to a stimulator delivering a high-frequency current, which is placed in the subclavian region. This therapeutic option can have spectacular results but today is applied only to patients facing a therapeutic impasse, i.e., those who experience uncontrollable complications deriving from levodopa therapy (motor fluctuations and dyskinesia). DBS can potentially generate severe complications (1 to 3% permanent neurological complications in the case of the best-trained medical teams), but nonetheless a positive benefit to risk ratio in favour of this technology is generally acknowledged in the literature. The emphasis is placed on the importance of very carefully selecting the patients (PD at the stage of severe motor complications, sensitivity to levodopa, age under 75 years, good overall condition, absence of cognitive disorders or progressive psychiatric disorders). There is currently some discussion about possibly extending the indication to less seriously affected PD patients.
DBS is a complex operation and requires multi-disciplinary management (neurology, neuroradiology, neurosurgery, neurophysiology and neuropsychology). The medical teams must have a very high level of expertise that cannot be improvised. Specialised equipment is required to accurately target the position of the electrodes. The complexity of the procedure and its follow-up makes heavy demands on the medical team, in particular the neurologists, and as such limits the acceptable number of procedures one centre can perform per year (ideally 25 procedures, maximum 50, minimum 12 to maintain the level of expertise).
The CEDIT file describes the organisation of patient management together with the procedures for quality care. It is recommended that a patient registry be established for monitoring the results of the treatment, in particular for analysing severe short-term complications (mortality, disability etc) and long-term developments. The elements described in the file make up the specifications for DBS centres. Additionally, it is suggested that the long-term follow up of implanted patients be performed by a network of specially trained neurologists.
The high cost of DBS surgery (in the region of € 33,000, more than 50 per cent of which relates to the implantable devices) and subsequent medical follow-up (additional cost of stimulator replacement € 12,000 every five to seven years, not counting the medical attention required for equipment adjustment and possible complications) must be compared with the long-term benefits arising from reduced treatment with drugs and fewer hospital stays, enhanced quality of life for patients (autonomy with regard to routine tasks , restored family and social life and possible return to work ). The provisional results of the SPARK study are in favour of surgery: the average six-monthly medical costs for a patient receiving surgery are € 6,840 prior to surgery and € 2,280 after surgery i.e., a figure close to the average six-monthly cost for treating PD patients regardless of the stage reached (€ 2,350).
France is the leading European country in terms of patient access to this new technology. So far, 16 centres in France perform DBS for Parkinson's disease. The number of PD patients who have undergone surgery in France has increased significantly: on December 31st, 1998, the total number of patients that had been implanted was 124 and was up to 959 by 30th June, 2002. It is worth noting that five of these centres began this type of activity well ahead of the others and perform two thirds of all the operations of this type in France (Grenoble University Hospital - the initiator of the technology -, Lille University Hospital, Marseilles University Hospital, Pitié-Salpêtrière Hospital in Paris, Henri Mondor Hospital in Créteil).
Extrapolating from available data to obtain the rate of activity for the whole of 2002 (the latest survey results pertained to the first half of 2002) produces a figure of 350 patients. On 30th June 2000 there was 757-patient waiting list in France as compared to 640 on 30th June 2002.
An epidemiological survey was carried out in the northern region of France (Nord-Pas de Calais) to assess the number of patients suffering from Parkinson's disease for whom DBS would be appropriate.
Extrapolating from the results for this region to the whole of France, the INSERM 360 team (director: Annick Alpérovitch) came to the following conclusions (on the basis of the current 11 criteria for DBS eligibility): the annual number of DBS indications (new cases) is estimated to be in the region of 150 in France (medium hypothesis), ranging between 104 cases (lower hypothesis) and 192 cases (upper hypothesis). Since access to DBS has so far been limited, the potential number of patients is estimated to be approximately 2300. Furthermore, a variation analysis for the eligibility criteria shows a very strong impact since by introducing maximum flexibility for selection purposes (with only five criteria), the number of patients liable to undergo thorough investigations for the purpose of validating the indication is multiplied by a factor of six.
By drawing together the theoretical data on activity with the data deriving from the activity estimate as well as the results of the epidemiological survey, the available capacity in France can be assessed as follows:
- The present rate of activity (of the order of 350 patients in 2002) is not very far removed from the ideal theoretical level for about 15 centres - an average rate of 25 operations per year per centre would come to 375 patients;
- This theoretical value for capacity is more than sufficient in terms of accommodating incidental cases if we refer to current eligibility criteria. However, were indications to be extended to patients less seriously affected by Parkinson's disease, or to treatment of other diseases, the situation would have to be reassessed;
- Concerning the management of prevalent cases (in the region of 2300 patients), the mismatch between the potential and actual waiting list (2300 vs. 640) can be explained on the basis of two assumptions: 1) by definition, an epidemiological survey of this type detects cases that had not been identified by the health care network 2) it is believed that a sort of "self-censorship" is exercised by medical teams to avoid excessive build-up on waiting lists. Managing the "stock" of prevalent indications is a different matter from managing incidental indications for DBS. This stock comprises some 640 patients that are known to be waiting for DBS, no doubt a conservative figure as noted above. These patients are currently considered to have an indication for DBS and should, ideally, undergo surgery in the very short term. In the present state of knowledge, we cannot establish for how many of those patients, the DBS indication will eventually disappear (in view of co-morbidity, worsening of PD, etc), nor when, but it is likely that in five years time some of those patients will no longer be able to benefit from DBS.
This suggests that an immediate effort should be made to provide these PD patients with this innovative treatment and attempt to absorb current waiting lists while rapidly providing for incidental indications.
RECOMMENDATION
* Patient management throughout the therapeutic chain - establishing the indication, surgery itself, follow up of patients - requires a stringent approach and faultless organisation.
* The possibility of extending DBS indications to less seriously affected PD patients and to other diseases is critical in view of the impact thereof on capacity.
* One DBS centre per region, concentrating the highest level of expertise for these procedures, would appear to be a reasonable objective. This notion should of course be adjusted according to population density so that these centres are evenly distributed throughout France. Long-term monitoring of patients with DBS implants should be designed on the basis of a network of skills.
* Supervisory authorities should make arrangements for the specifications to be validated and subsequently monitored so as to guarantee the quality of the DBS centres.
¹ The CEDIT report disregards other diseases for which DBS is performed - dystonia, essential tremor - as well as DBS conducted under research protocols relating to epilepsy, Tourette Syndrome, obsessive-compulsive neurosis.
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