Successful deep brain stimulation of the subthalamic nucleus may have unforeseen effects on the ability to swim in some patients with Parkinson’s disease, according to findings from a case series of nine patients published in Neurology.
All nine patients in the report were experienced swimmers, including two who competed in several competition-level races. They reported losing their ability to swim after successful deep brain stimulation of the subthalamic nucleus (STN-DBS) procedures. The Neurology paper focuses on three of the patients.
All of the patients achieved good to excellent motor control and cut their L-dopa dosage by impressive amounts. But they also lost the ability to coordinate limb movement when in the water, reported Daniel Waldvogel, MD, of the University of Zurich, and associates.
“All found their ability to swim came back immediately, with improved coordination of the limbs,” when stimulation was discontinued, the team noted. But soon after the stimulation ceased, their motor symptoms also rapidly returned, leading all to resume continuous stimulation.
One possible explanation is that STN-DBS does not strongly improve dopamine levels in the supplementary motor area, which controls independent limb movements.
It “may be that DBS affects the supplementary motor area (SMA) differently than levodopa. The SMA is a main output area of the basal ganglia, with connections to the primary motor cortex and the spinal cord,” wrote Dr. Waldvogel and associates. “Functionally, the SMA is thought to be crucial for facilitating independent movements of the limbs, which is a key requirement for swimming.”
Although the SMA also partly manages gait, walking was unaffected in all nine of the patients.
The authors described three patients in more detail:
- Case 1 was a 69-year-old man who was a proficient swimmer before DBS. His Unified Parkinson’s Disease Rating Scale (UPDRS) motor score on medication fell from 28 with dyskinesia before DBS to 17 after DBS, and his levodopa-equivalent dosage declined from 1,570 mg to 920 mg. The man almost drowned after he jumped into a lake and had to be rescued by another swimmer.
- Case 4 was a 59-year-old woman who was an accomplished and competitive swimmer and had been swimming up until the DBS procedure. After DBS, her UPDRS motor score on medication fell from 9 with dyskinesia to 6, and her levodopa-equivalent dosage dropped from 825 mg to 150 mg. She had good motor outcome after DBS but lost the ability to swim. “She regularly practiced swimming with her physiotherapist, but never came close to her previous level,” the authors said.
- Case 5 was a 61-year-old woman who was a competitive swimmer, including swimming across Lake Zurich, and held a lifesaving certification. Her UPDRS motor score on medication fell from 11 with dyskinesia to 9, and her levodopa-equivalent dosage decreased from 800 mg to 180 mg. After DBS, she could swim only a quarter of a kilometer and complained of “awkward posture” during her efforts.
The phenomenon has been reported just one other time by a group from the University of Western Australia. This reported patient was a 68-year-old man with a 5-year history of medication-refractory, tremor-predominant Parkinson’s. He received DBS of the posterior subthalamic area (PSA-DBS).
The patient was a dedicated lap swimmer at his local pool. When he returned to his hobby, “he quickly realized he could not propel himself adequately and that he required assistance to get to safety. In a supervised swimming situation, he was unable to float or perform freestyle, breaststroke, or back stroke. With the stimulator turned off for 30 minutes, he regained swimming ability and lost it when the stimulator was turned on.
The Australian team noted that three similar cases presented to them, but they did not discuss those cases in the paper.
Dr. Waldvogel and coauthors wrote that they might also have unreported cases in their cohort of patients with STN-DBS.
“Our cohort of patients with PD who underwent STN-DBS at the time of this retrospective study consisted of 217 patients, but we did not assess patients systematically for their swimming skills or loss thereof,” the authors said. “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 report received no funding, and one author disclosed financial relationships with industry.
SOURCE: Waldvogel D et al Neurology. 2019 Nov 27. doi: 10.1212/WNL.0000000000008664.