Chronic Deep Brain Stimulation in Parkinson’s Disease
abstract & commentary
Source: Haberler C, et al. No tissue damage by chronic deep brain stimulation in Parkinson’s disease. Ann Neurol 2000; 48:372-376.
Over the last five years, there has been an exponential increase in the number of patients with Parkinson’s disease undergoing implantation of deep brain stimulators. Three main targets are available for stimulation: the thalamic ventral intermediate nucleus (VIM), the subthalamic nucleus (STN), and the internal globus pallidus. Currently, the VIM is the only target approved by the Food and Drug Administration (FDA) for implantation. However, as discussed previously in Neurology Alert (Frucht S. Neurol Alert 1999;18:15-16), the STN is increasingly being accessed as the target of choice, as chronic stimulation of this nucleus improves all of the cardinal features of dopa-responsive parkinsonism, including tremor.
Commentary
Deep brain stimulation (DBS) was serendipitously discovered to produce clinical benefit when early stereotactic neurosurgeons stimulated potential targets prior to creating a surgical lesion. DBS offers several advantages to ablative surgery. The effects of stimulation are reversible, and DBS offers the opportunity to adjust the patient’s stimulation parameters in order to obtain the maximum clinical benefit. DBS can be performed on both sides of the brain, whereas the risks of neurological or cognitive deficits from bilateral thalamotomy or pallidotomy are unacceptable. There may also be a slightly reduced surgical risk with DBS compared to surgery in which lesions are placed.
The mechanism by which DBS produces functional benefit is unknown. Application of electrical current has been postulated to interfere with or change the functional circuitry of the target nuclei and its connections. One major concern is that chronic DBS might injure or permanently damage the target nuclei. In this important paper, Haberler and colleagues report on eight Parkinson’s disease patients who were implanted with DBS devices. Four patients underwent bilateral stimulation; in six, the VIM was targeted, and two underwent STN implantation. Stimulation was performed for up to 70 months. In all cases, death was unrelated to stimulation.
After removal of the stimulating electrodes, all brains were formalin-fixed, and the electrode tract and target nuclei were closely examined for evidence of gliosis, inflammatory reaction or neuronal loss. There was no evidence of damage to brain parenchyma in any patient.
These results are especially important given the number of patients who are likely to undergo implantation in the next decade. It should be noted, however, that only two STN patients were included in this series. It will be important to extend these observations in future studies to a larger cohort of STN patients. For now, though, DBS appears not only to be a superior alternative to ablative lesioning for patients with Parkinson’s disease, but also to be safe as well. —Steven Frucht
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