**4.4 Deep brain stimulation and spinal cord stimulation**

DBS surgeries are often used for treating movement disorders such as Parkinson's disease, dystonia, and essential tremor as well as psychiatric disorders such as obsessive–compulsive disorder. In the other hand as cases of chronic lumboischialgia and failed back surgery syndrome are rising, spinal cord stimulation surgeries are getting more attention. Both procedures involve implanting electrodes and neuromodulators in different sites, therefore these surgeries are carrying a high risk of infection. Infection rates are different in different areas and hospitals, in the literature the infection rate for DBS surgeries can be up to25%. As mentioned before *S. aureus* is the most common cause of neurosurgical infections and DBS and SCS surgeries are not an exclusion of this fact [12].

Intraoperative topical use of vancomycin has shown no advantage in preventing postoperative infections and its use intraoperatively remains controversial, in fact Bernstein et all in 2019 concluded that intraoperative topical use of vancomycin increases the risk of postoperative infection after electrode implantation [12].

Infection of brain electrodes can lead to abscess formation and spinal electrode infection can cause epidural abscess formation. Neuromodulators can also get infected and be a source for septic reactions.

#### **4.5 Screws, rods and cages**

The most common implants used in spine surgery are screws, rods and intervertebral cages. Different materials such as polypropylene-polyester, titanium, and polyetheretherketone (PEEK) are used in spinal surgeries and a study in 2019 revealed that the above-mentioned materials among all other materials used in neurosurgical procedures have the highest rate for infection [9]. Fusion surgeries require the removal of the intervertebral disk and implantation of an intervertebral cage, this in turn can cause spondylodiscitis which in turn can cause colonization and infection of the implanted screws and cages. The ongoing inflammation causes loosening of implanted screws, and this will lead to spine instability, therefore in such cases patients need to be immobilized, treated with antibiotics and revision surgery should be done when suitable. In addition, using thoracolumbar spinal orthosis (TLSO) braces can add some degrees of spine stability and fine patient mobilization can be allowed when wearing TLSO. Diagnosing is based on elevated inflammatory parameters on blood tests as well as contrast enhanced MRI scans to visualize the spinal canal and assess the extent of ongoing inflammation.

#### **4.6 Treatment**

Foreign body infection requires immediate attention and treatment; if left untreated it can cause severe intracranial or epidural inflammation and severe neurological deficits as well as sepsis and multi organ failure consequently. Diagnosing foreign body infection requires precise imaging, multiple repeated blood tests, culturing and patient examination. Once the diagnosis of foreign body colonization or infection has been made, broad spectrum empirical systemic antibiotic treatment should be started immediately and later on modified based on antibiograms. If the infection is caught in early phases and only mild symptoms are present and imaging modalities rule out presence of abscess or empyema and colonization of foreign bodies are not suspected then systematic or intrathecal antibiotic treatment might be enough to treat the infection, but in cases were abscess or empyema formation is already present on scans or CRP-PCT levels are not normalizing with antibiotic therapy, then removal or revision of the implanted foreign bodies are required.

Infected V-P shunts need to be removed and CSF divergence with EVD is preferred at a different site rather than the primary surgical site. In cases where deep brain electrodes need to be removed, patient management can become very challenging; for example, patients who suffer from Parkinson's disease and are nonresponders to oral medication, will have severe disabilities if their neuro pacemaker was turned off suddenly and there was no pacing in the subthalamic nuclei. When infections are properly treated, then permanent electrodes, shunts or any other foreign body should be reimplanted if the patient's status and treatment require so.
