Conference Coverage

Troubleshooting Gait and Voice Problems After DBS for Parkinson’s Disease

The approach to symptom control may change according to whether the symptom results from the disease or the stimulation.


LAS VEGAS—In patients with Parkinson’s disease, deep brain stimulation (DBS) can improve gait significantly and reduce vocal tremor. Some patients may fail to improve following implantation, however, and others who do improve may later worsen. In such cases, neurologists can address problems with gait and voice tremor using various steps to optimize DBS treatment, according to two lectures delivered at the 21st Annual Meeting of the North American Neuromodulation Society.

Refractory Gait Impairment

Gait impairment and freezing of gait may persist for years in some patients, despite DBS treatment at the traditional frequency of 130 Hz. Studies by Moreau and colleagues indicate that stimulation at 60 Hz improves these outcomes in previously refractory patients, said Helen M. Brontë-Stewart, MD, MSE, the John E. Cahill Family Professor and Director of the Stanford Movement Disorders Center at Stanford University School of Medicine in California. Research by Ricchi et al shows that low-frequency DBS also reduces gait impairment and freezing of gait in the early stages after implantation.

Helen M. Brontë-Stewart, MD, MSE

The factors that predict which patients will benefit from low-frequency DBS of the subthalamic nucleus (STN) are increased age, severe axial phenotype at five years after surgery, and lower preoperative levodopa responsiveness. But low-frequency DBS may not be adequate to improve other motor signs such as tremor, said Dr. Brontë-Stewart. Improvements on low-frequency DBS also may not last long.

The literature about which part of the STN should be stimulated for more effective treatment contains mixed results. Several investigations, including a 2011 study by McNeely et al, showed that high-frequency DBS is most efficacious when applied to the dorsolateral margin of STN. Other studies, including one performed by Dr. Brontë-Stewart and colleagues, indicate that stimulating the ventral area of the STN is more effective. Khoo et al found that 60-Hz stimulation was superior to 130-Hz stimulation for axial motor signs in Parkinson’s disease. “Clearly, we do not have consensus,” said Dr. Brontë-Stewart.

Postsurgical Gait Worsening

If a patient’s gait worsens shortly after DBS surgery, one possible explanation is that the leads were misplaced. Gait also could worsen if high-frequency DBS is applied outside the STN, especially in the anterior, medial, and dorsal regions, said Dr. Brontë-Stewart. If a patient’s gait and akinesia worsen with high-frequency STN DBS, but his or her tremor and rigidity improve, the cause may be diffusion of the stimulatory field into the pallido-fugal fibers before decussation of the pallido-pedunculopontine nucleus (PPN) pathway.

“The combination of STN DBS and medication may lead to lower-extremity dyskinesias,” which may account for gait worsening in some patients, said Dr. Brontë-Stewart. “It is important to look at these patients off medication. It may show that the dyskinesias are interfering with the gait studies, and whether the medication is affecting their cognition, which may also worsen gait.”

Patients’ gait and balance may worsen years after implantation. For example, stimulation-resistant axial symptoms may emerge after five years of DBS even if treatment remains effective for appendicular symptoms. This outcome may follow progression of the disease into nondopaminergic networks. Another possible cause is increased voltage that involves pallido-fugal pathways, thus enlarging the field of stimulation, said Dr. Brontë-Stewart.

For patients with delayed worsening, Dr. Brontë-Stewart advises that “if you reprogram DBS, focusing on gait symmetry, you can improve gait, including freezing of gait. Many of us program DBS for appendicular symptoms, and we fail to do this for gait…. Perhaps use bipolar or interleaving programming to restrict field extension.”

Preoperative improvement in Unified Parkinson’s Disease Rating Scale Part III scores in response to levodopa treatment is the best predictor of the effect of DBS on gait and freezing of gait. Improvement in freezing of gait following STN DBS has, in turn, been related to reduced medication dosing and lack of worsening of cognition, concluded Dr. Brontë-Stewart.

An Initial Approach to Vocal Tremor

The literature suggests that in patients with Parkinson’s disease, STN DBS often results in deterioration of speech that may not improve when the stimulation is stopped. Predictors of vocal problems include presurgical dysarthria, duration and severity of presurgical disease progression, and contact placement around the left STN.

“There is no large evidence base upon which to work when you are trying to … deal with someone who comes to you with speech problems,” said Bryan T. Klassen, MD, Assistant Professor of Neurology at the Mayo Clinic in Rochester, Minnesota. Addressing potential speech problems before implantation “should be a major part of any DBS protocol,” he added. A neurologist should document a patient’s pre-existing speech issues carefully. At Mayo Clinic, all patients scheduled to undergo implantation visit a speech pathologist first, and the examination is recorded.

In addition, patients need to understand that vocal tremor may be a symptom of Parkinson’s disease and may not result from DBS. On the other hand, neurologists also should inform patients that inserting the leads may cause dysarthria even before the battery for the device is implanted. Patients ultimately may have to choose between optimal tremor control and optimal speech, said Dr. Klassen.

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