A common myth about DBS is that it only treats tremor. In fact, DBS treats most motor symptoms of Parkinson’s disease, including slowness, stiffness, and slow walking in addition to tremor. Furthermore, it also treats dyskinesias, which are involuntary excessive movements characterized by writhing or jumping that can occur in long-term use of levodopa (aka Sinemet). Lastly, it improves motor or so-called “ON/OFF” fluctuations. Over time, patients may find that levodopa does not last as long or its effects are more unpredictable, alternating between periods of good mobility or “ON time” when the medication is working and periods of relative immobility or “OFF time” when the medication seems to have little to no effect. DBS mitigates the highs and lows of medication treatment producing more consistent symptom control. In regards to non-motor symptoms, the outcomes are more uncertain, but in general, they do not respond to DBS. These would include cognition, mood, swallowing and speech as well as others.
There are several misconceptions surrounding the effect of DBS on gait and balance, both negative and positive. While it is true that balance problems (termed postural instability) and gait freezing have less of a response, typically if they improve with medications (“ON” state) they can also improve with DBS. Generally speaking, any motor symptom that improves with levodopa can respond to DBS. Symptoms that do not respond to levodopa usually do not improve significantly with DBS with the exception of tremor. Thus, a patient in the later stages of PD and wheelchair bound despite medications, will likely have a poor response; while a patient who only freezes during the OFF period will likely have a good response. There is also the notion that DBS will worsen these symptoms. However, this is more likely due to progression of the disease, which DBS does not prevent, or if it is due to stimulation, changing programming parameters can easily alleviate the side effect.
In the past, DBS was reserved for those with advanced and severe symptoms. However, this meant that patients struggled with a less than optimal quality of life for many years. Following a 2013 study published in the New England Journal of Medicine, which looked at patients implanted earlier, the FDA approved the therapy for mid-stage Parkinson’s. That still begs the question, “when should I consider DBS?” If levodopa and other antiparkinsonian agents are effective and maintaining a good quality of life, one would continue with medical management. However, if complications arise (as those described above), or if medications cause side effects or are not enough (particularly in the case of tremor) such that the quality of life is no longer acceptable, surgery should be considered. What that point is depends on the individual. For example, what is acceptable for a patient that is retired can be very different from a patient who is still working.
Candidacy can be a complex decision so we use a multidisciplinary team consisting of neurologists, nurse practitioner, neurosurgeon, neuropsychologist and a neurophysiologist to aid in the process. We take into consideration the following:
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The majority of patients who undergo DBS experience a significant reduction in the Parkinson symptoms, and many are able to reduce their medications though the amount varies between individuals. Researchers following patients long-term have found continued motor improvement even up to 10 years post-implantation. However, we must emphasize that DBS is not a cure for Parkinson’s disease nor does it slow down the progression. While DBS will continue to treat tremor, slowness, stiffness and dyskinesia, other symptoms such as balance problems, gait freezing, speech and swallowing difficulties, and dementia may still occur. As such it is important to have realistic expectations so that one understands the complexity of the treatment and avoid disappointment.