The clinical definition of infection due to hardware of DBS system was purulence or erythema identified from any DBS incision site (cranial, retro-auricular, or IPG), which was subsequently confirmed with a positive culture . In neurosurgery and other surgical areas, DM has been noted as an independent risk factor for the development of postoperative surgical infection [4, 5]. To diagnose an infection, at least one of the following is required: (1) purulent drainage, (2) organisms isolated from an aseptically-obtained culture, (3) at least one of the following signs or symptoms of infection: pain or tenderness, localized swelling, erythema or heat, fever (>38°C), or spontaneous dehiscence, (4) an abscess or other evidence of infection that is detected on gross anatomical or histopathological exam or on an imaging test, (5) diagnosis of an surgical site infection(SSI) by a surgeon, attending physician, or other designee [6, 7]. Our patient met all criteria other than fever. The main differential diagnosis is allergic reactions with symptom onset usually occurred between eight days and three years after implantation. The most commonly reported presentation of hypersensitivity was skin changes over the site of the IPG. Although hypersensitivity reactions are rare, implanting physicians should remember the distinguishing features of an allergic reaction, such as a normothermic body temperature, blood tests (white blood cell count, erythrocyte sedimentation rate and inflammatory markers such as C-reactive protein) within normal limits, negative bacterial cultures, and no response to antibiotics .
The sites of infection tend to be around the IPG, connector in retro-auricular site or cranial burr hole, while intracerebral infection seems to be rare. A study retrospectively analysed complications after the first month postoperatively in 249 patients treated with DBS for a period of 16 years. The results showed that infection was the most common delayed complication, while IPG was the most common involving location . Most infections seemed to arise from the IPG within 2 months of implantation, with the majority caused by Staphylococcus species. Each patient underwent 1–5 salvage procedures. Another study involved 13 patients who underwent a total of 32 incisions and drainage procedures for the hardware salvage prior to the final resection. Of the cranial and connecting site infection, more than half occur in the retro-auricular connector site . Staphylococcus species are the most common offending organism. Obtaining intraoperative cultures in all cases of infection in order to dictate appropriate antibiotic management was recommended .
In cases of infection all attempt should be made to salvage the DBS leads. Infection at the IPG site and/or extension lead connector would likely necessitate hardware removal of everything except for the DBS leads and treatment with a six weeks course of intravenous antibiotics. Skin erosion or infection at the cranial wound would be treated with debridement, change of stimlock base plates and six weeks of intravenous antibiotics. Exposed lead wire without infection would require wound revision, antibiotic irrigation, and isolation of the lead from the skin incision . Fortunately, most of the infections responded to antibiotic therapy and/or surgical debridement. Only a fraction of these patients had intractable infection or inflammation that made removal of hardware components inevitable . In DBS related SSI, there has been a policy to try a conservative approach to avoid unnecessary hardware removal. Our case suggests prompt local hardware removal and long-term antibiotic treatment when an infection caused by Staphylococcus aureus was suspected. Decolonization has been shown to be effective in reducing the risk of intracranial infection, especially for the deep SSI.
If infection recur, then most experience is that complete removal of the hardware is inevitable even after prolonged antibiotic treatment, although we acknowledge that others had reported success with partial removal of the hardware and prolonged (up to six weeks) intravenous antibiotics. A total of 362 patients underwent 530 electrode placements by three neurosurgeons in a study period. Of these, 16 (4.4%) underwent ≥ 1 DBS revision surgical procedures due to infection. Despite hardware salvage attempts, 15 of the 16 infected patients (93.8%) subsequently underwent complete device explantation due to recurrent infection. Seven patients (53.8%) underwent DBS reimplantation after explantation and resolution of infection. The mean length of time between explantation and reimplantation was 5.7 ± 3.0 months. Rates of complete and partial hardware salvage success are estimated to be only 30% and 21% respectively, and complete DBS system explantation is frequently needed . The clinical benefits provided by DBS are significant, while hardware explantation may lead to loss of efficacy and exacerbation of symptoms . This is particularly problematic for PD patients, who are at significant risk of developing life-threatening DBS withdrawal syndrome when stimulation continues for several years [14, 15].
In a cross-sectional study using individual-level data provided by the Australian Government, they evaluated 1849 patients identified as having PD and implanted with DBS over a 15-year period. 51.4% of patients required repeat hardware surgery. 11.3% of patients had repeat intracranial electrode surgery. 47.6% of patients had repeat IPG/extension-cable surgery including for presumed battery depletion. Repeated hardware procedures, including those for intracranial leads, are therefore common . A retrospective, single-centre analysis of 123 consecutive patients treated with DBS was conducted. Four patients (3.3%) had their IPG removed due to infection .
In one study, researchers present there outcomes after revision or reimplantation surgery in patients with infections, device failure, or unsatisfactory results after DBS surgery for PD. Reimplantation after surgical infection seems feasible and overall safe . When they analyzed patients who had the device removed and reimplanted due to infection, they did not notice significant differences in outcome, suggesting that reimplantation after infection can be successfully accomplished. Although management of infection is costly, it seems possible to recapture the initial benefit of DBS after reimplantation .
The problem in our case was that brain atrophy led to ventricular dilatation, gliosis of former electrode pathways, and atrophy of the nucleus, which made target localization and trajectory selection difficult. These changes are consistent with moderate degradation, particularly in the medial-edge portion of the STN. One study compared the lateral parts of STN of patients treated with DBS with that of nine non-DBS treated PD patients, the former showing moderate astrogliosis, microglial activation, thickening of neuronal processes, and changes in neuronal shape, size and density around the STN. In contrast to short-duration DBS, chronic DBS may elicit moderate degeneration of the stimulated target neuronal tissue after up to 16 years of stimulation. It remains unclear whether these changes are related to chronic depolarization block or an alteration of the synaptic conduction or other causes including the mere physical proximity of a foreign body, which is a matter of speculation . Typical findings include fibrous sheaths of 5-25 mm surrounding the electrode track, a chronic inflammation with reactive astrocytes, multinucleated giant cells, macrophages, mononuclear leucocytes and T-lymphocytes, fibrillary gliosis and Rosenthal fibers . Glial scarring around DBS leads in the brain has been described previously and this is thought to be the result of an inflammatory response of microglia to the leads . Our case and similar results suggest that positive clinical outcomes can be reproduced following extraction and reimplantation of bilateral DBS leads by adjacent trajectories within the STN .
Reasons for not re-placing the lead include cognitive decline after the original surgery, patient choice, comorbidities, and the threat of hardware erosion in patients with compromised skin integrity at the surgical site. When complete explantation is eventually performed, the experience of failed salvage attempts may contribute to the decision by these patients to not undergo DBS system reimplantation, leading to permanent loss of stimulation benefit. The cost of new IPG type accounted for about 80% of the cost of the whole DBS system and it was higher than that of earlier non-rechargeable models. All of these highlighted the need for long-term follow-up and ongoing patient/carer education, especially for patients with rechargeable IPG implants .