SURGICAL-TREATMENT OF PARKINSONS-DISEASE

At present, there are three major surgical approaches to Parkinson's d isease (PD): (1) Ablative surgery (i.e. pallidotomy, thalamotomy); (2) deep brain stimulation (DBS) of the thalamus, internal globus pallidu s (GPi) and subthalamic nucleus (STN); and (3) grafting fetal mesencep halic cells into the striatum. As a result of increasing understanding of the pathophysiology of the basal ganglia and the demonstration of surgical alleviation of experimental parkinsonism, surgery has regaine d a paramount importance in the management of PD. The aim of pallidoto my and is to reduce the excessive inhibitory output from the GPi and s ubstantia nigra reticulata (SNr). Pallidotomy and DBS of the STN or GP i aim to reverse the pathophysiological consequences of dopamine defic iency in PD, and should be considered entirely symptomatic treatments. The ideal candidates for pallidotomy are young patients in good gener al health in whom dyskinesias are the main reasons for disability. Pat ients with severe bilateral problems uncontrollable with present pharm acological tools are candidates for DBS. As yet, there are no formal d ata to help decide how to choose between GPi and STN stimulation. In o ur practice, patients are allocated to GPi stimulation when 'on' dyski nesias are extremely severe. In most other instances, we prefer to per form STN stimulation. At present there is almost no reason to decide f or the thalamic stimulation since tremor is equally arrested by STN st imulation, which in addition improves all other features of PD. Equall y the only indication for thalamotomy would be a patient with long-sta nding tremor as the main clinical manifestation, which can not be cont rolled with drugs. The proportion of patients in whom the thalamus wil l be the preferable target for either DBS or thalamotomy is small (les s than 5%). Grafting aims to repair the nigrostriatal pathway and rest ore dopaminergic function in the striatum. In the future implants cont aining not only dopaminergic cells but also growth factors and a varie ty of other substances could become a method to not only functionally compensate the biochemical abnormalities of PD but also to arrest its progression. This technique is limited to a few centres around the wor ld owing to the technical, logistical and ethical problems of obtainin g and handling embryonic cells. At present, grafting of dopaminergic c ells is perhaps best suited for patients with young-onset PD (less tha n 45 years old) who are at high risk of developing complications withi n a short time of beginning pharmacological treatment and in whom the idea of making lesions or implanting electrodes into the brain for dec ades seems less appealing. Consideration of surgery in any given patie nt should be weighed against the risks (about 1% mortality and 2-6% of severe morbidity-hemiplegia, cognitive deficit, speech problems, etc. ) associated with these techniques. The development of better imaging methods and the growing expertise of multidisciplinary teams will undo ubtedly make surgery for PD safer and more effective in the future.