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Abstract
The number of patients with deep brain stimulation (DBS) devices implanted is increasing. Although practices vary between centres, patients are typically given training and information from their DBS nurse or clinician, as well as a comprehensive device manual and contact details for their device manufacturer. However, for the lifetime of a patient with a DBS system, most of their secondary care often occurs in a centre without a co-located DBS service. The local neurologist is often asked pragmatic questions regarding the do’s and don’ts for patients with DBS systems. While a DBS centre or device manufacturer can provide advice, we thought that it will be helpful to outline the overall management of DBS for movement disorders and the approach to commonly raised questions. We describe briefly the clinical application of DBS and discuss common scenarios where there are possible compatibility issues around the device.
- Parkinson’s disease
- movement disorders
- electrical stimulation
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What is deep brain stimulation?
Deep brain stimulation (DBS) involves the surgical implantation of electrodes into specific anatomical targets (usually bilaterally and symmetrically) to modulate pathogenic signalling pathways in certain diseases to improve the patient’s symptoms. The electrodes are connected via extension wires (embedded subcutaneously) to an implanted pulse generator, usually positioned below the collarbone in adults. The stimulation parameters are controlled by a remote external neuromodulator platform and the patient is usually given their own controller that links to their device. A small, modifiable electrical field is generated from selected contacts at the tip of the electrode to modulate nerve transmission of the adjacent tissue (see figure 1). The most common clinical applications are Parkinson’s disease, essential tremor and dystonia, although some centres offer DBS for Tourette’s syndrome and obsessive–compulsive disorder, with novel targets also being developed for new indications. We hope that readers will find this article to be a helpful introduction into this field, but stress that much of the content is ‘expert opinion’ rather than ‘evidence-based’. Device manufacturers and local centres vary in their device constraints and practice, sometimes considerably, and so, while this article outlines common themes, their advice should be sought on individual cases.
The components of a DBS device (courtesy of Boston Scientific, reproduced with permission). The leads are implanted to the anatomical target, fixed to the skull and the extracranial wires are then pulled through under the skin where they are then connected to the implanted pulse generator. DBS, deep brain stimulation.
How are patients with DBS managed?
Patients are selected for DBS according to commissioning criteria (where applicable, eg, NHS England criteria) and local expertise on the balance between potential benefits and adverse effects. Individualised counselling is key to ensuring that patients have realistic expectations, and thus make informed decisions about treatment. Target selection and implantation techniques vary considerably between centres, discussion of which is beyond the scope of this article. Following implantation, electrical activation involves systematically exploring the stimulation settings to determine the optimally positioned electrical contact and waveform parameters to maximise clinical benefit, while minimising any stimulation-induced side effects. Between ranges of parameters set for their hand-held DBS programmer, patients can often modify their settings at home with their controller to help to hone the best settings further. DBS allows for the continuous stimulation of the target which, in some cases, may be sufficient to negate the need for adjunctive medical treatment in tremor or dystonia, at least initially. Drug treatments are typically required in Parkinson’s (in part due to the additional pathways modulated by dopamine replacement therapies) and may need adjusting as the disease progresses. One can conceptualise the clinical effects of DBS as being analogous to the continuous delivery of medication aimed at alleviating symptoms, but with downstream firing patterns being modified electrically rather than pharmacologically. Using Parkinson’s as an example, stimulation of the subthalamic nucleus mimics the effect of dopaminergic medications on the motor symptoms: primarily tremor, bradykinesia and rigidity. In patients with motor fluctuations, continuous stimulation allows for a reduction in motor ‘off’ time and an increase in ‘on’ time without dyskinesias, due to a reduction in dopaminergic medication (see figure 2).
Graphical representation of the effect of DBS in Parkinson’s. These graphs conceptualise the downstream effects of dopamine replacement therapy and subthalamic nucleus stimulation. (A) In early Parkinson’s, the large therapeutic window allows a good response from each dose of levodopa without motor complications. (B) As Parkinson’s progresses, the therapeutic window narrows, requiring multiple dosing at larger doses to maximise benefit. Despite fractionating the levodopa dose, motor fluctuations can occur due to excessive or subtherapeutic dopamine levels leading to dyskinesias or ‘off’ symptoms, respectively. (C) Due to the effect of DBS, smaller and less frequent doses of levodopa are required to achieve benefit and maintain the patient within the theraputic window, and thus avoid or minimise motor fluctuations. DBS, deep brain stimulation.
Following optimisation of stimulation parameters, onward management of any residual symptoms (such as titration of dopaminergic medication in Parkinson’s) should continue as per the usual practice, bearing in mind that lower medication doses may be needed. For patient convenience, as well as potential capacity issues, patients are often managed jointly between the DBS centre and the local Parkinson’s team (see figure 3).
This flowchart outlines the usual timeline for a patient with Parkinson’s referred for DBS to the movement disorders team in Bristol, UK; timings vary between centres. DBS, deep brain stimulation.
We would also highlight that while symptoms of Parkinson’s and essential tremor respond promptly to neuromodulation, the effects on dystonia can be delayed and take several months to become apparent. A deterioration in symptom control should prompt referral to the DBS centre for consideration of re-programming the stimulator, as the optimal settings may change over time. However, due to progressive neuronal damage, there is a limit to the symptom control possible.
What can go wrong?
Problems with DBS can be divided into acute surgical complications, poor stimulation response and side effects, and hardware problems.
Acute complications of implantation surgery are similar to that of other neurosurgical procedures, including cerebral haemorrhage (1.1%) and stroke (0.4%), although serious complications are rare (in total <3%).1 Clinicians should be vigilant of the potential for infection postdischarge, in addition to fever and changes around the wound sites, headache, changes in behaviour or consciousness and focal neurological symptoms should prompt urgent assessment. New neurological symptoms or suspicion of an infection should prompt urgent referral to neurosurgery. In the context of infection, the implanted pulse generator and/or electrodes may have to be removed, although re-implantation may be possible after a delay.
The key factors that influence outcome include patient selection, targeting and programming. Some patients may not achieve the improvement of their symptoms expected preoperatively. Technical considerations may be responsible, such as suboptimal lead positioning or individual anatomic variability. The parameters required for optimal symptom improvement can cause persistent side effects. For example, potential adverse effects when targeting the subthalamic nucleus include dysarthria, dysphagia and postural instability, which can limit the stimulation parameters. The use of ‘directional’ leads is a recent innovation aiming to improve outcomes by narrowing the field of stimulation to be focused in a particular direction rather than circumferentially, thus allowing more selective modulation of the targeted pathways.
Sudden loss of stimulation due to hardware failures, such as a faulty implanted pulse generator, loose connections or fractured leads (eg, after a fall or traumatic injury), occur infrequently but can cause a sudden worsening of symptoms. The DBS centre should be contacted to check the device for faults and, if necessary, check the hardware using X-rays.
Newer devices have rechargeable batteries that last for more than 15 years, non-rechargeable devices usually last between 2 and 5 years, depending on the settings. The patient controller can be used to check the battery. A low battery warning is issued months before it is fully depleted, prompting the patient to contact their DBS centre for replacement before this occurs. Despite these precautions, there are occasional cases where the battery depletes completely. The sudden loss of stimulation can trigger an akinetic crisis in Parkinson’s disease patients and a dystonic storm in patients with dystonia. These complications can be life-threatening and should be treated as a medical emergency with the usual medical therapies, and the DBS centre contacted so that stimulation can be restarted at the earliest possible opportunity.
Can patients with DBS have MRI scans?
MRI scanning is possible with some, but not all, devices within certain constraints. Some devices allow for MRI scanning of certain parts of the body only, such as head scanning being possible while imaging below the neck is not. All hybrid systems (mixed components from different manufacturers) are incompatible. The risk relates to the implanted hardware heating due to the magnetic field, and thus causing damage to adjacent tissues. Each device manufacturer produces guidelines that state the MRI compatibility of their products and the prerequisite scanning parameters. Patients are all given a registration card that confirms the make and model of the implanted device. There is no published evidence of MRI-associated adverse events in DBS patients when manufacturers guidelines are adhered to.
If an MRI is required, we suggest contacting the DBS centre for advice on compatibility in the first instance, but it may be preferable to perform the scan at the site of DBS surgery in order to ensure that all criteria for safe scanning are met (see figure 4). Some DBS manufacturers stipulate a requirement for impedances below a certain threshold for MRI scans to be performed. The radiographers would need the device details so that they can check that the MRI machine coil and field strength (usually 1.5 T) are compatible. The device manufacturers produce guidelines (available online, details below) that include device-specific eligibility criteria, which should be used in addition to the standard MRI safety questionnaire. A clinician can be required to perform a check of the implanted pulse generator before scanning to check for faults, but this is not necessary for some of the newer models, which perform this check automatically when set for MRI mode.
Flowchart outlining our recommended approach to MRI scanning. DBS, deep brain stimulation.
The stimulator must have the voltage (or current) set to 0V and the device switched off before scanning, or switched to an ‘MRI mode’, using the patient controller. We always recommend that the device stimulation parameters are turned down completely before being switched off for scanning or procedures, in case it is aberrantly turned on during the event. Patients should, therefore, receive adequate medical therapy to control any re-emergent symptoms. Scanning should be avoided if the patient has a fever, and clothing/coverings should reflect the need to avoid overheating. During scanning, the patient should be asked to report any changes or new symptoms to allow problems to be identified early and the scan stopped immediately.
Are there any limitations on other forms of imaging or neurophysiological tests?
Some DBS devices may need to be switched off for X-ray imaging, such as DEXA scans. Also, for mammograms, the pads should not be placed so as to put pressure on the device or leads (similar to managing cardiac pacemakers). Manufacturers report that radiation from CT scanning potentially can increase stimulation during the procedure or even damage the stimulator if on; they, therefore, recommend that devices are turned off for scanning (as per MRI scanning above). For diagnostic ultrasound scanning, the transducer should not be placed directly over the DBS device, which may need to be turned off to limit interference with the scanning.
The stimulator should be turned off before performing an EEG, nerve conduction studies or electromyography, as it interferes with recordings.
What precautions are needed around minor procedures and surgery?
Most, if not all, DBS centres recommend antibiotic prophylaxis for patients with DBS devices undergoing dental, gastrointestinal and genitourinary procedures (including urinary catheterisation) where there is a potential risk of infection. For example, our protocol advises prophylactic co-amoxiclav for dental procedures. However, we are not aware of any current specific guidelines on preventing secondary infections of DBS systems, and there is a lack of scientific evidence underpinning this ‘expert opinion’ practice. There are similar issues surrounding implantable electronic cardiac devices but the recommendations for antibiotic prophylaxis differ.
Some DBS devices are not compatible with the use of electrocautery (surgical diathermy), and specific directions for use should be sought from device manufacturers before any potential operation. Monopolar electrocautery carries a higher risk of electrical charge being transferred to surrounding tissues compared with bipolar electrocautery. Some DBS manufacturers contraindicate using monopolar electrocautery as it may cause conduction of charge through the DBS leads, leading to tissue damage. Other manufacturers allow its use providing specific guidance on intraoperative set up is followed. When surgical diathermy is used, the stimulator should have the voltage reduced to 0V and then be switched off, to prevent inadvertent delivery of current during surgery.
The stimulator should also be switched off for any procedure involving lasers. Lithotripsy is relatively contraindicated as it may damage the circuitry, but if it must be used, then the beam should be as far from the hardware as possible (check with the device manufacturer for the minimum distance).
‘Therapeutic diathermy’ (not to be confused with electrocautery as described above) is the use of shortwave, microwave and ultrasound diathermy; it is explicitly contraindicated in any patient with any form of implanted DBS hardware. This can lead to the transfer of energy to the electrodes causing tissue damage, and there have been case reports of permanent injury and even death.
Dental procedures can involve the use of dental turbines or ultrasound descalers; device-specific advice is again available from the manufacturers. Care should be taken to avoid this equipment being placed over or near the DBS hardware as there have been case reports of the dentist accidentally deactivating the stimulator.
Can patients with DBS have radiotherapy?
The use of radiotherapy for targets that may overlap with DBS hardware has not been studied extensively, with only a few case reports in the literature. Manufacturers state that radiotherapy may permanently damage DBS hardware, but there are no guidelines or thresholds for safe radiation exposure levels. In the three published cases, radiotherapy was used to target lung cancer and brain metastases. These targets overlapped with DBS implanted pulse generator/leads in each case, but radiotherapy did not lead to interference or damage to the DBS.
Previous studies have analysed how radiotherapy interferes with implantable electronic cardiac devices, with increasing radiation dose correlating with damage to implanted hardware.2 We can infer from this a similar effect in DBS devices. Radiotherapy can probably be conducted safely in DBS patients; however, increasing doses of radiation correlates with the likelihood of damage to DBS hardware. We recommend multidisciplinary care between the DBS team and the oncologist on an individual case basis.
What specific issues relate to cardiology?
Special consideration for patients with DBS needs to be given in the interpretation of ECGs, internal and external cardioversion, and cardiac pacemakers.
The placement of the implanted pulse generator subcostally means that the field generated can interfere with the ECG trace. In one published case, this has led to the delayed diagnosis of myocardial infarction. To minimise the artefact during ECG recording, DBS systems should, if possible, be switched off using the patient controller. If it is not possible to switch off the DBS system, ECG artefact can be reduced by placing the implanted pulse generator in a bipolar setting, by contacting the patients" DBS team, or by modifying ECG settings to a low-pass filter.,
The primary risk associated with external electric cardioversion or defibrillation in DBS patients is brain tissue damage, caused by current conducted through DBS electrodes. There is a single case study in which this occurred: a DBS patient underwent electric cardioversion for atrial fibrillation, which caused permanent tissue damage around the site of brain electrodes leading to intractable central dysaesthetic pain. However, in this case, the defibrillator pads were placed very close to the patient’s implanted pulse generator, which was not switched off. Conversely, cases in which a patient’s implanted pulse generator was set to 0V and switched off, or was placed in a bipolar setting before cardioversion did not result in neurological injury, or implanted pulse generator interference.
We suggest that the patient’s implanted pulse generator should be set to 0V and switched off, as with surgical procedures, and also set to bipolar mode. The defibrillator pads should be placed as far as possible from the implanted pulse generator. The DBS system should be checked after defibrillation for evidence of interference. Of course, the presence of DBS hardware should not take precedence over the need for potentially life-saving defibrillation/cardioversion in an emergency.
Cardiac pacing may be hazardous in DBS patients. The pacemaker may misinterpret the electrical impulses produced by DBS implanted pulse generators as cardiac arrhythmia. This could potentially lead to life-threatening dysregulation of cardiac pacing. There are reports of patients with monopolar DBS settings suffering acute ventricular arrhythmias following cardiac pacemaker implantation, which resolved once DBS settings were adjusted to bipolar mode. Other studies have also reported the safe use of implantable electronic cardiac devices if the DBS system is placed in a bipolar mode. Therefore, based on the small number of published case reports available, we recommend contacting the DBS team for adjustment to a bipolar setting (if not already in use) before implanting the cardiac advice. If only monopolar DBS settings are possible, patients should be admitted for observation following co-implantation of the cardiac device. The DBS and cardiac devices should be implanted as far away from each other as possible. The presence of a cardiac pacemaker in itself is not a contraindication to DBS implantation,3 although the device would need to be compatible with the preoperative MRI required.
Are there any precautions when travelling?
Patients are advised not to pass through security scanners. Security scanners will not harm the device but they have been reported to switch stimulation on or off. They can also cause a momentary change in stimulation (as can theft detectors in shops) and some of our patients have described this phenomenon even walking around the outside of the scanner, so we recommend keeping a good distance. Security personnel at airports will conduct a manual security screen instead of requiring the patient with DBS to go through the security gate. We recommend that patients always carry their device registration card when travelling and take the patient controller in the hand luggage, so they can switch off the stimulator if necessary.
Are there any precautions needed activities at work, home or recreation?
Once the skin has healed following surgery, usual activities can be resumed. Patients should be cautious with any sport that may risk the device being struck with force (such as boxing or martial arts) and they should consider wearing helmets if there is a potential risk of head injury (such as cycling or horse riding).
Most DIY tools and home appliances are perfectly safe (such as microwave ovens) but there are a few important exceptions encountered around the work and the home. Essentially any device that is capable of generating a significant electromagnetic field should be kept at a distance, as it can cause the device to switch off inadvertently.4 These devices include (but are not limited to) induction cooking hobs and heaters, theft detectors, large audio speakers, arc welding equipment, power lines and power generators. Some older cordless phones and mobile phones may do the same. Electric and hybrid cars could potentially create electromagnetic interference, possibly depending on the make and model of the car, leading to manufacturers to issue a warning for patients considering travelling in one. While there is a case report of interference, the overall risk remains unknown as, to the best of our knowledge, this has not been specifically tested by manufacturers. If there is any doubt about safety, the device manufacturer should be contacted. It is also possible that proximity to some of these devices can interfere with the connection between the patient controller and the stimulator.
Key points
MRI can be performed for some patients with implanted deep brain stimulation (DBS) devices (in MRI mode or with the stimulation parameters turned down completely and then the device switched off); this is best done at the DBS centre.
People with DBS devices may need prophylactic antibiotics for minor procedures (such as dental work).
Device-specific restrictions should be checked before planned use of surgical diathermy; the stimulation parameters should be turned down completely and then the device switched off during such procedures.
Hardware failure (such as a depleted battery) may require emergency medical treatment for the underlying movement disorder; the DBS centre should be contacted urgently.
If there is doubt about the safety of an activity or healthcare intervention, seek advice from the DBS centre or device manufacturer.
The management of patients with DBS, especially when treating Parkinson"s, requires joint care between the local hospital and the DBS centre.
Footnotes
Contributors FB: researched, outlined the scope and drafted the manuscript. TR: researched and helped to draft the manuscript. LM, CR and CN provided expert critique and practical insights. NB provided technical expertise and critiqued the manuscript. KS-K and AW provided expert technique and practical insights. All the authors contributed to the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer All the authors have approved the final article. FB and TR report no financial disclosures. CN and CR have received conference expenses from Boston Scientific. LM has received honoraria from Boston Scientific, Medtronic, Abbott and AbbVie. KS-K has received travel and conference expenses from Abbvie, Boston and Merz, as well as speaking honoraria from Abbvie. NB has received honoraria from Abbott and Boston Scientific. AW has received costs for attending scientific meetings from Boston Scientific and Medtronic.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Commissioned. Externally peer reviewed by Tom Foltynie, London, UK.