Weighing the Risks of Deep Brain Stimulation

Deep brain stimulation (DBS) has been heralded as one of the most remarkable breakthroughs in the treatment of movement disorders. However, while DBS serves up myriad benefits, it can be associated with various other medical complications — including other movement disorders. Studies have shown that new movement disorders can emerge during or after stimulation. So, do the risks of DBS outweigh its benefits, or are the adverse ramifications of DBS uncommon enough to overlook as rare or unlikely occurrences?

Disorder by DBS

DBS has been known to generate other movement-related disorders such as dyskinesias, blepharospasm, and hypokinesia. Globus pallidus internus (GPi)-DBS can lead to a hypokinetic gait disorder with freezing of gait (FOG).¹ According to researchers José Baizabal-Carvallo, MD, and Joseph Jankovic, MD, of the Parkinson’s Disease Center and Movement Disorders Clinic, department of neurology, Baylor College of Medicine, Houston, Texas, “Dyskinesias, blepharospasm, and apraxia of eyelid opening have been described mainly with subthalamic nucleus stimulation, whereas hypokinesia and FOG have been observed with stimulation of the GPi.” Other types of dyskinesia may also be observed with stimulation of the globus pallidus externus and ataxic gait. However, these movement disorders are generally reversible and can usually be resolved in the absence of stimulation.²

In a retrospective long-term research study of 123 patients, the possible adverse effects of DBS were explored.³ The indications for DBS surgery were tremors, Parkinson disease (PD), Tourette syndrome, Huntington disease, and dystonia. Of the 123 consecutive and non-preselected patients observed, 106 exhibited 433 adverse effects. Among the most frequently reported were gait and speech disturbances. Serious adverse events that surfaced within 4 weeks of surgery could be reversed. The only DBS-induced irreversible adverse events were observed in patients with PD, who constituted less than 5% of the study population. Of interest, most of these irreversible effects were non-motor symptoms, but mild gait and speech disturbances were commonly reported with ventral intermediate nucleus of thalamus (VIM) stimulation.               

According to the American Association of Neurological Surgeons, DBS surgery does pose certain risks and result in adverse events, but these tend to be mild and reversible.⁴ For instance, the risk for brain hemorrhage is 2% to 3%, which may be either insignificant or lead to major complications such as speech impairment, paralysis, or stroke. An individual who has undergone DBS may experience movement-related adverse events such as a loss of balance, marginal paralysis, jolts and shocks, and reduced coordination. It is not uncommon for patients to experience heightened tremors in the aftermath of DBS surgery. These are further compounded in patients who are older than 70 or have comorbidities.⁴

Neurologist Julia Muellner, MD, attending neurologist in movement disorders, University Hospital, Bern, Switzerland, told Neurology Advisor, “Risks associated with DBS include bleeding, infection, or misplaced device complications. But associated risks depend on the stimulated brain structure. In subthalamic nucleus (STN), it may be apathy or impulsivity when the lower contacts of the electrode are activated. Also, balance and speech may deteriorate after DBS.”

Weighing Risk and Benefits

As with any surgery, there are risks involved in using DBS. However, DBS has been associated with significant improvements in the quality of life for many patients living with motor functionality deficiencies. It has been particularly successful in tremor control and the elimination of dyskinesia, a common adverse event with drug therapy.⁵  According to Dr Muellner, “DBS offers constant therapy for movement disorders without taking drugs every other hour and suffering from their systemic side effects. This is especially the case after STN-DBS, where Parkinson’s patients may significantly reduce their drug intake and adapt their therapy exactly to their needs, as they can adapt the stimulation for their left and right extremities independently.”

According to a report by Dr David Breen, movement disorders Fellow at  Toronto Western Hospital in Canada, and colleagues,⁶ DBS is effective in the treatment of various movement disorders and psychiatric conditions. However, the holistic outcomes are dependent on several factors, including oral medication regimens, disease progression, existing comorbidities, stimulation parameters, and electrode placement.

The investigators followed the evolution of 4 patients who underwent DBS surgery and found that despite successful DBS surgery, they suffered from functional movement disorders for a range of reasons.⁶ For example, a 51-year-old patient with PD exhibited comorbid anxiety and social phobia prior to her DBS surgery. Post-surgery complications arose due to a sudden functional irregularity in her right leg in the form of involuntary kicking triggered by sitting down. One of the other patients, a 37-year-old man, had bilateral DBS (Cg25) of the subcallosal cingulate gyrus for treatment-resistant depression. He needed a system re-implantation because of a hardware infection after a year. His depressive symptoms, however, did show improvement post-surgery. At the time of the second surgery, he had comorbid chronic body pain and post-surgery complaints including tremors, balance impairment, and functional leg weakness.

Based on their observations, the researchers concluded that patients often appeared to struggle subconsciously to adapt to rapid changes in functionality post-DBS surgery. Therefore, psychological maladaptation can trigger symptoms of movement disorder. At the same time, symptoms that persist despite DBS implantation suggest that other contributors may include comorbidities, reduced medication, direct stimulation effects on limbic pathways, altered body image, and unmet expectations. Often, patients get their hopes up, expecting a cure and complete reversal of their condition, when in reality, DBS is not a cure but a remedy to relieve certain symptoms of progressive conditions. In most cases, DBS does not reverse the condition or arrest progressive disease.⁶

The National Parkinson Foundation reports, “The risk of serious or permanent complications from DBS therapy is very low.” Stroke from bleeding in the brain constitutes a very small risk, and some patients may experience long-term challenges like numbness, slurred speech, and problems with vision. Temporary and reversible symptoms — such as short-term movement and speech problems like dyskinesia or a temporary deterioration in movement, balance, and speech — are more common than any permanent conditions. In rare cases, these symptoms can become permanent.⁷

Striking the Right Balance

DBS may not work for everyone, but experts say it is largely safe, with any complications being rare, temporary, and reversible. The success of DBS is dependent on certain conditions and circumstances. Timing is everything — when a patient undergoes DBS, the process must be carefully planned in consultation with a specialist. Furthermore, pre-existing comorbidities, mental health, and patient expectation management are all critical considerations in the decision to take the DBS route.

References

1. Schrader C, Capelle HH, Knife TM, et al. GPi-DBS may induce a hypokinetic gait disorder with freezing of gait in patients with dystonia. Neurology. 2011;77(5); 483-488.
2. Baizabal-Carvallo JF, Jankovic J. Movement disorders induced by deep brain stimulation. Parkinsonism Relat Disord. 2016;25:1-9.
3. Buhmann C, Huckhagel T, Engel K, et al. Adverse events in deep brain stimulation: A retrospective long-term analysis of neurological, psychiatric and other occurrences. PLoS ONE. 2017;12(7).
4. American Association of Neurological Surgeons. Deep brain stimulation. 2018.www.aans.org/Patients/Neurosurgical-Conditions-and-Treatments/Deep-Brain-Stimulation. Accessed June 5, 2018.
5. Neurology Solutions.Medtronic deep brain ztimulation: precision, risks & results. 2018. www.neurologysolutions.com/parkinsons-disease/medtronic-deep-brain-stimulation-surgery-results-2. Accessed June 5, 2018.
6. Breen DP, Rohani M, Moro E, et al. Functional movement disorders arising after successful deep brain stimulation. Neurology. 2018;90(20):931-932.
7. Okun SM, Zeilman PR. Parkinson’s disease: guide to deep brain stimulation therapy. National Parkinson Foundation. 2017. www.parkinson.org/sites/default/files/Guide_to_DBS_Stimulation_Therapy.pdf. Accessed June 4, 2018.