By: David Bartczak, Member, MPF Board of Directors, Michigan Parkinson Foundation and Support Group Facilitator, Royal Oak Support Group; with Dr. Kelvin Chou, MD, Member MPF Professional Advisory Board and Assistant Professor, University of Michigan Medical Center and Richard Trosch, MD, Member, MPF Professional Advisory Board, and Director, Parkinson's and Movement Disorders Center, Southfield, MI
Deep Brain Stimulation (DBS) is not a cure, but rather an option to be considered when conventional pharmaceutical approaches no longer provide the quality of life the patient desires. Often, a patient is referred for DBS because he experiences wearing-off or dyskinesias that cannot be controlled with further medication adjustments. Patients with severe tremor may also qualify for DBS. Unfortunately, not every Parkinson's patient is a suitable candidate for DBS.
Many DBS centers employ a team approach, in which a movement disorders neurologist, a neurosurgeon and other staff screen potential patients in order to select candidates most likely to benefit from the surgery. The purpose of this article is to inform you of the evaluation criteria for a DBS candidate. The main criteria can be broken down into the four "D"s.
Diagnosis: The patient must have a diagnosis of Parkinson 's Disease. Many other neurological disorders may mimic the symptoms of PD, including Multiple System Atrophy (MSA), Progressive Supranuclear Palsy (PSP) and Dementia with Lewy bodies (DLB). Some physicians will also use the term "parkinsonism" when they are unsure if a patient truly has PD. The diagnosis is important because patients with these other disorders do not benefit from DBS. An essential part of the DBS evaluation is a consultation with a neurologist specializing in PD to ensure the correct diagnosis.
Dopaminergic response: Patients should respond to dopaminergic medications. PD patients initially show a stable response to medications in the first few years of the disease. However, as their disease severity progresses, the medication's benefit duration may shorten and the Parkinson's symptoms return before the time for the next dose. This phenomenon, called wearing-off, can sometimes be corrected with medication adjustments. Patients may also develop dyskinesias over time. These involuntary, fidgety-type body movements can be severe. When patients begin to experience disabling wearing-off or dyskinesias not correctable with changes to medication, it is time to consider DBS. It is important to remember that, in general, DBS only makes patients as good as their best medication "on" state, but it also helps decrease the severity of the "off" times, allowing patients to feel as if they are "on" throughout the day. The exception to this rule is tremor. Parkinsonian tremor can be treated with DBS even if it does not respond to medications. Some DBS centers may test dopaminergic response with an off-on evaluation, in which patients are examined 12 hours after stopping their PD medication and then an hour or two after taking it. To be a suitable candidate for DBS surgery, a patient should have at least a 30-point improvement between the non-medicated/"off" state and the medicated /"on" state on a Parkinson's disease rating scale score.
No Dementia: Patients who have evidence of dementia or significant problems with thinking and memory are not candidates for DBS. That is because patients with significant cognitive problems may have difficulty fully understanding all the risks and benefits of surgery. There are cases in the medical literature where patients with borderline dementia progress to full-blown dementia after DBS surgery. As a result, part of the DBS evaluation may include neuropsychological testing to be certain that patients do not have severe problems in this area.
No uncontrolled Depression: Some patients have been reported to be suicidal after DBS surgery for PD. While it is not exactly clear why this happens, it is reasonable to make sure patients do not have significant depression before undergoing surgery.
Other factors that may impact whether someone is offered surgery include age and medical history. While there is no absolute cutoff for age, younger patients tend to do better. The preferred age is younger than 70, since the surgery and recovery times become longer for more elderly patients, but many DBS centers have operated on patients older than 70 with good results. Multiple medical problems may also make the surgery more challenging. For example, a history of brittle diabetes can affect healing of the incisions. Presence of a pacemaker may also make the surgery more difficult, because MRI is often used to visualize the area where the electrode will be placed. These are issues to discussed with the neurologist and neurosurgeon during the evaluation process.
Selection of the proper candidates is one of the keys to success for DBS surgery. However, a patient's expectations must also be realistic for the surgery to be successful. DBS will only be as good as the best medicated state prior to surgery. PD symptoms that do not respond to medications, such as gait or balance, also will not benefit from DBS. DBS can be a life-changing procedure, but only for the right patients.