Electron microscopy of tissue adherent to explanted electrodes in dystonia and Parkinson's disease

Deep brain stimulation (DBS) is used to treat a variety of severe medically intractable movement disorders, including Parkinson's disease, tremor and dystonia. There have been few studies examining the effect of chronic DBS on the brains of Parkinson's disease patients. Most of these post mortem studies concluded that chronic DBS caused mild gliosis around the lead track and did not damage brain tissue. There have been no similar histopathological studies on brains from dystonic patients who have undergone DBS. In this study, our objective was to discover whether tissue would be attached to DBS electrodes removed from patients for routine clinical reasons. We hoped that by examining explanted DBS electrodes using scanning (SEM) and/or transmission (TEM) electron microscopy we might visualize any attached tissue and thus understand the electrode-human brain tissue interaction more accurately. Initially, SEM was performed on one control DBS electrode that had not been implanted. Then 21 (one subthalamic nucleus and 20 globus pallidus internus) explanted DBS electrodes were prepared, after fixation in 3% glutaraldehyde, for SEM (n = 9) or TEM (n = 10), or both (n = 2), according to departmental protocol. The electrodes were sourced from two patients with Parkinson's disease, one with myoclonic dystonia, two with cervical dystonia and five with primary generalized dystonia, and had been in situ for 11 and 31 months (Parkinson's disease), 16 months (myoclonic dystonia), 14 and 24 months (cervical dystonia) and 3-24 months (primary generalized dystonia). Our results showed that a foreign body multinucleate giant cell-type reaction was present in all TEM samples and in SEM samples, prewashed to remove surface blood and fibrin, regardless of the diagnosis. Some of the giant cells were >100 microm in diameter and might have originated from either fusion of parenchymal microglia, resident perivascular macrophage precursors and/or monocytes/macrophages invading from the blood stream. The presence of mononuclear macrophages containing lysosomes and sometimes having conspicuous filopodia was detected by TEM. Both types of cell contained highly electron-dense inclusions, which probably represent phagocytosed material. Similar material, the exact nature of which is unknown, was also seen in the vicinity of these cells. This reaction was present irrespective of the duration of implantation and may be a response to the polyurethane component of the electrodes' surface coat. These findings may be relevant to our understanding of the time course of the clinical response to DBS in Parkinson's disease and various forms of dystonia, as well as contributing to the design characteristics of future DBS electrodes.