An unexpected, and potentially life-threatening, side effect of deep brain stimulation for Parkinson disease (PD) has surfaced. A case series of nine PD patients who had been surgically implanted with subthalamic nucleus deep brain stimulators (STN-DBSs) shows that although the device improved other movement symptoms, patients' swimming skills deteriorated. "Awareness is the most important goal" of highlighting these cases, senior investigator Christian Baumann, MD, of the University of Zurich in Switzerland, told Medscape Medical News. "Neurologists treating patients undergoing deep brain stimulation in the subthalamic nucleus should know that this potentially life-threatening side effect might occur on stimulation." "Until more research is done to determine why some people with deep brain stimulation can no longer swim, it is crucial that people be told now of the potential risk of drowning and the need for a carefully supervised assessment of their swimming skills before going into deep water," study coauthor Daniel Waldvogel, MD, said in a statement. The cases were published online November 27 in Neurology. Deeper Dive Needed All nine patients had been proficient swimmers even after their having been diagnosed with PD, and some had even been competitive swimmers. In one instance, a 69-year-old PD patient who was an experienced and proficient swimmer had to be saved from drowning. The man reportedly felt confident about his ability to swim because his STN-DBS device had improved his motor abilities, so much so that he "literally jumped into the lake." On dry land, all nine patients in the case series were "highly satisfied" with their motor outcomes and neuropsychological function after DBS surgery. However, in the water, they lost the ability to perform the breaststroke, backstroke, or crawl. Three of the nine patients turned off their DBS implants and were immediately able to swim. However, because their other movement symptoms worsened, they switched on their devices as soon as possible. "Swimming is a highly coordinated movement that requires complicated arm and leg coordination. Exactly how deep brain stimulation is interfering with this ability needs to be determined," said Waldvogel. Previous research has shown that either DBS or levodopa can improve simultaneous task execution in PD patients, and the fact that "several patients lost their ability to swim was therefore unexpected, particularly because the surgical procedure was considered successful, given the improvement in motor symptoms and quality of life," the researchers note. The investigators used intraoperative microelectrode recordings, macroelectrode test stimulation, and postoperative imaging to rule out electrode migration as a potential cause of the phenomenon. Baumann said there is a concern that this side effect may not be limited to swimming. "We have found that complex motor behaviors which have been learnt and are co-regulated by basal ganglia structures may be affected. Apart from swimming, this might, for instance, also include skiing, playing golf, and skating." "Until the mechanism of the reported deterioration of the ability to swim after STN-DBS is elucidated, it is crucial that we advise patients of the potential risk of drowning and the need for a carefully supervised assessment of their swimming skills before going into deep water," the investigators write. The research is ongoing. "We have started looking at the interplay between neuronal signaling, different motor behaviors, and deep brain stimulation, and we will follow this route," Baumann said. Waldvogel noted that the report includes only a few cases and that more research is necessary. "Even though these reports affected only a few people, we felt this potential risk was serious enough to alert others with Parkinson's disease, as well as their families and doctors," he said. Network Effect? Commenting on the report for Medscape Medical News, Leo Verhagen, MD, PhD, Rush University in Chicago, Illinois, noted that this finding echoes a single case report from Australia published in 2016 in which a PD patient was unable to coordinate arm, leg, and trunk movements while swimming. "As in the present study, this patient had been an excellent swimmer and regained his skills when stimulation was turned off," said Verhagen. "Apparently in some patients, DBS interferes with the automatic, smooth execution of coordinated movements that are essential in swimming. The fact that this has not been recognized earlier suggests that this issue does not occur universally after DBS," said Verhagen, who is also director of the Movement Disorder Interventional Program, Rush University Medical Center. Verhagen pointed out that the proficient swimmers in the report represent a subpopulation. "Not all patients with Parkinson's disease swim, and of those who do, there may have only been a few who considered themselves good swimmers in the past, and even fewer who considered themselves still good swimmers immediately prior to surgery. "So, it is entirely possible that impaired coordination of limbs and trunk during swimming occurs in many individuals after DBS but has gone largely unnoticed," he said. He added that the investigators should be "commended for not letting this potential hazard escape our attention." Also commenting on the findings, Mitra Afshari, MD, MPH, an assistant professor of neurologic sciences at Rush University, said that clinically, the results are "very relevant in terms of the day-to-day care of our patients and the recommendations we make for postoperative care. "This case series of PD patients with subthalamic nucleus DBS stimulation causing rapid, and reversible, inability to swim is very interesting, and from my perspective reflects the complexity of the subthalamic region," Afshari, who is also affiliated with the Parkinson's Disease and Movement Disorders Program at Rush, told Medscape Medical News. Although people commonly think of the STN as a distinct nucleus, "it is actually a white matter tract containing several diverse axons with varying inputs and outputs, carrying motor, limbic, and associative functions," he noted. "Another piece that would add to the discussion of these mysterious findings and perhaps provide further clarity" is if future research reveals similar effects when the globus pallidus-interna (GPi), a second target in PD, is stimulated, Afshari said. Verhagen agreed about looking beyond the STN. "The DBS target is perhaps less relevant: the earlier case report involved DBS in the caudal zona incerta ― the posterior subthalamic area, not the STN ― and the same study mentions three other, less documented cases of drowning after lesioning and/or DBS of thalamus and GPi. "This underscores that DBS has an impact on a network rather than just a specific area," he said. The investigators, Afshari, and Verhagen have disclosed no relevant financial relationships. Neurology. Published online November 27, 2019. Abstract Source
