16 SURGICAL APPROACH TO MOVEMENT DISORDERS Table 16.1 Idiopathic Parkinson’s Disease • Positive response to levodopa: a response of ~>30% to levodopa in off–on test usually indicates better prognosis7 • Tremor-predominant: even levodopa-unresponsive tremor tends to improve with surgery. • Patient has appendicular symptoms: rigidity, freezing, dystonia, bradykinesia. • Patient has dyskinesia while on medication. • On–off surgical fluctuations occur. • Patient has limited cognitive decline. • There is no major or severe and unmanaged psychiatric disorder. Table 16.2 Likely to Improve Less/Not Likely to Improve • Tremor • Gait • Rigidity • Sialorrhea/swallowing • Bradykinesia • Balance problems/falling • On–off fluctuations • Other axial symptoms • Freezing of gait (±) • Urinary/gastrointestinal symptoms Table 16.3 Primary Dystonia Secondary Dystonia Tardive Dystonia No evident underlying cause Associated with identifiable brain insult Associated with long-term neuroleptic administration Subset known to have DYT1 mutation Can be caused by stroke, trauma, toxin exposures Postsynaptic dopamine striatal receptors sensitized Potential candidates for bilateral DBS Mixed results with DBS May benefit from bilateral DBS
HISTORY OF SURGERY FOR MOVEMENT DISORDERS
In the 1950s, Cooper first described ligation of the anterior choroidal artery for the treatment of Parkinson’s disease (PD).1 In his series, tremor and rigidity improved in 70% of patients, while contralateral hemiplegia was noted in 11% and operative mortality occurred in 10%. This has been attributed to the variable vascular distribution of the anterior choroidal artery. This procedure fell out of favor because of its high morbidity rates and the efficacy of emerging treatment options.
During this time period, Spiegel and colleagues introduced a novel stereotactic method in which intracranial landmarks—in this case, the pineal gland and the foramina of Monro—were used to locate adjacent anatomical structures.2 In further studies, their stereotactic lesioning techniques were shown to be as effective as open procedures for the treatment of movement disorders, with a lower risk for complications.
Lars Leksell introduced posteroventral pallidotomy in the 1950s after noting better treatment of all three cardinal symptoms of PD (tremor, rigidity, and bradykinesia) with this technique than with anterodorsal pallidotomy. Outcomes of this procedure were described by Svennilson et al in 1960 and confirmed by Laitinen et al in 1992.3,4 Posteroventral pallidotomy was considered the standard of care for the treatment of PD before deep brain stimulation (DBS) became available.
When levodopa was introduced in the 1960s, the surgical treatment of PD declined in favor of medical management. However, the long-term use of levodopa is associated with several side effects, and over time, interest in surgical treatment options was renewed.5 During this period, significant advances in technology allowed improved imaging studies, microelectrode recording capabilities, and understanding of the underlying anatomy.
DBS was pioneered for movement disorders in the 1980s and became a preferred tool because of its reversibility and adjustability. The Food and Drug Administration (FDA) approved thalamic DBS for essential tremor and PD-associated tremor in 1997, followed by subthalamic nucleus (STN) and globus pallidus internus (GPi) DBS for PD in 2003.6
The remainder of this chapter will provide an overview of the surgical management options currently available for the treatment of movement disorders, with an emphasis on DBS.
SURGERY FOR SPECIFIC MOVEMENT DISORDERS
Surgical procedures do not treat the cause of movement disorders, and to date, they have not been shown to alter the natural history of the disease. Surgical procedures are aimed at alleviating the symptoms of some movement disorders in order to improve quality of life.
Stereotactic procedures for the symptoms of PD include ablative procedures and DBS of several cerebral targets, predominantly the thalamus, globus pallidus, and subthalamic area.
DBS is also currently approved by the FDA for the management of essential tremors and, under a Humanitarian Device Exemption, for the treatment of primary dystonias.6
The stereotactic methods for probing the brain are similar whether the intent is to produce a radio-frequency thermolesion or to deploy an electrode for chronic electrical stimulation (DBS).
In addition, noninvasive techniques, such as radiosurgery, are an option for the ablation of subcortical targets in some cases.
Surgical management of some movement disorders can lead to the mitigation of motor symptoms and improvement in daily function for patients with advanced disease, resistance to medication, or unmanageable side effects. When patients are counseled regarding the surgical treatment of movement disorders, it is very important to stress that movement disorders have two distinct categories of symptoms: motor and nonmotor (ie, cognitive and behavioral).
The goal of all movement disorder surgery is to attempt to control the motor symptoms and minimize nonmotor adverse effects.
It is important to have an open discussion with the patient and family regarding which symptoms are more likely to improve and which symptoms will not or are less likely to improve. It should also be explained that surgery is not curative.
Keep in mind that the appeal of technology and invasive treatment can give some patients the impression that surgical intervention is curative.
As with all surgical procedures, patient selection can influence outcomes. In our experience, we find that multidisciplinary evaluation is helpful in determining candidates who are likely to respond from a motor standpoint with a lower risk for nonmotor complications.
The multidisciplinary team may include neurologists, neurosurgeons, neuropsychologists, and physical and/or occupational therapists. A psychiatrist evaluates patients for whom behavioral comorbidities are a significant concern, and a bioethicist is involved as needed.
This multidisciplinary evaluation has several goals.
Although it may sound obvious, confirmation or reevaluation of the diagnosis is an important first goal. It is not rare for patients to be labeled with a diagnosis for several years, and revisiting often leads to a change in the primary diagnosis and treatment plan.
The team reevaluates the current and past treatment regimens. Some patients may benefit from pharmacologic optimization only and may not require surgery.
A detailed cognitive evaluation can determine the degree of cognitive decline, which may correlate with risk for postsurgical worsening.
The risk for negative effects of surgery on nonmotor symptoms is related not only to the procedure and insertion of the leads but also to chronic stimulation of these complex subcortical targets.
Parkinson’s Disease
GENERAL INDICATIONS (TABLE 16.1)
Advanced movement disorder
Poor symptomatic management with drugs
Drug-induced side effects
Manageable comorbidities
Typical Surgical Candidates With Parkinson’s Disease
Parkinson Symptoms Likely or Unlikely to Improve With Deep Brain Stimulation
Ability of the patient to understand the goals, risks, possible benefits, and limitations of surgery and the available alternatives to surgery
GENERAL CONTRAINDICATIONS (TABLE 16.2)
Dementia, major cognitive decline
Severe or unmanaged psychiatric/behavioral disorder
Note: Depression and anxiety are common. They are not contraindications per se if managed.
Poorly controlled medical comorbidities
Clotting disorders that cannot be managed perioperatively
Requirement for anticoagulation or anti-aggregation therapy that cannot be stopped
Inability to adequately follow-up at the specialized center (greater limitation for DBS than for ablative treatments)
Essential Tremor: General Indications and Contraindications
As with other neurological disorders, the first-line treatment is medical management.
DBS for essential tremor is generally noted to have good outcomes; the outcomes for secondary tremor are not as good.
DBS of the ventral intermediate nucleus (VIM) can be offered to patients with poorly managed tremor.
The severity of tremor that “requires” surgery varies from person to person. The goals and needs depend on the patient’s occupation, hobbies, and personal interests. Secondary (nonessential) tremor can be treated with DBS (off label), but the outcomes tend to be limited.
Patients with distal tremor are thought to have a better prognosis.
Dystonia: General Indications and Contraindications (Table 16.3)
Primary generalized dystonia, with or without known genetic mutation (ie, DYT1).
Primary torticollis.
Success of Deep Brain Stimulation in Different Types of Dystonia
Significant disability related to dystonia.
Failure of nonsurgical management, including oral drugs, botulinum toxin injections.
SURGICAL TREATMENT OPTIONS AND SYMPTOM MANAGEMENT
DBS implantation is the most common procedure for the treatment of movement disorders in the United States. DBS has largely supplanted ablative techniques, but some patients are still good candidates for ablative treatment (Table 16.4).
The two most common ablative procedures used for movement disorders are radio-frequency (RF) ablation and gamma knife radiosurgery (GKRS).
The size of the lesion created with RF ablation can be tailored to a certain extent.
Frequent neurological examinations are usually conducted while RF ablation is performed to minimize risk of unforeseen effects due to the lesion created.
In GKRS, a focused beam of ionizing radiation from multiple locations is used with a high level of precision to create the lesion.
Some advantages of GKRS are that patients are discharged home on the day of the procedure and that it can be used for patients who are otherwise not good surgical candidates because of comorbidities.
Because of the nature of the ionizing radiation that creates the lesion, the clinical results associated with GKRS are not immediately visible to the patient and may take weeks to become apparent.
Although ablative procedures are not as commonly performed as DBS, they do have some advantages that should be considered in certain situations.
Patients do not have any implanted hardware that can be susceptible to erosion or infection.
Patients do not require as frequent follow-up for the adjustment of stimulation (but continue to require medication adjustments and follow-up). This is especially useful when patients are not able to follow up regularly with the movement disorder team.
DBS has largely replaced ablative procedures like thalamotomy and pallidotomy as standard of care for the treatment of movement disorders because DBS is reversible and does not create a permanent lesion. In addition, the stimulation can be modulated, and the location of the lead can be revised if necessary.7 On the other hand, implanted hardware is associated with risks. It is important to note that the goal for each of the preceding procedures is similar. Each technique has specific benefits and limitations.
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