Selection of Centers, Disorders, and Patients for Movement Disorder Surgery

4 Selection of Centers, Diseases, and Patients for Movement Disorder Surgery

Leo Verhagen Metman

Surgery for movement disorders has gained momentum over the last decade, catalyzed by the advent of high-frequency deep brain stimulation (DBS).1,2 Owing to its reversible nature, DBS is considered a safer method than ablative surgery.³ Nonetheless, several risks are associated with DBS, some are related to the procedure and hardware, others to the actual stimulation.^4–7 Hardware problems such as lead fracture and migration occur, and hemorrhage and infection can be intraoperative or postoperative problems. Additionally, a variety of cognitive, behavioral, psychiatric, and speech abnormalities have surfaced in the DBS literature.^8–11 Postoperatively, DBS is a costly and time-intensive therapy. Taken together, this list of problems serves as a reminder that DBS, just like ablative surgery, should only be undertaken after carefully weighing risks and benefits for each individual patient.¹² As with any elective surgery, patients and physicians are faced with options that need to be carefully considered as part of a patient selection process that will lead to the best outcome possible. In addition to medical considerations, other factors may play a role in determining whether surgery is the most appropriate treatment option. Nonmedical factors such as economic feasibility and governmental directives are not universal and are therefore not discussed here. Instead, the chapter focuses on a theoretical model which assumes that DBS is the surgical procedure of choice.^13,14 In this case, three “selections” need to be made as discussed in the following sections: (1) the selection of the optimal surgical center, (2) the selection of the appropriate disease amenable to surgical treatment, and (3) the selection of the optimal candidate for surgery.

Selection of a Center

The first pivotal component of successful surgery is the selection of a center consisting of a multidisciplinary team that is trained and experienced in the multifaceted management of patients with movement disorders.6 Only when such an infrastructure is in place can the patient expect to be appropriately diagnosed, evaluated, and treated with the highest chance of a good outcome.⁹ The ideal team should consist of several members whose roles in the preoperative, intraoperative, and postoperative periods are briefly discussed here.

Preoperative Period

Movement Disorder Neurologist

A movement disorder neurologist should provide the initial evaluation for any patient that is referred for consideration of a neurosurgical procedure. This key member of the surgical team provides invaluable expertise in diagnostic matters and knowledge of pharmacological as well as surgical treatments for movement disorders. During this visit the neurologist will (1) confirm the diagnosis through a detailed history and physical examination, (2) decide whether pharmacological approaches have been appropriately maximized, (3) determine whether the patient’s symptoms can likely benefit from surgical treatment (which may include additional visits to evaluate patients with and without their medications), and (4) determine if the potential benefits outweigh the risks for a particular patient. Following this thorough assessment, the neurologist will provide an opinion to the patient and family and advise them accordingly. Should the neurologist deem surgery appropriate, the patient will be referred to the team’s neurosurgeon.

Neurosurgeon

Neurosurgeons will usually rely on the movement disorder neurologist in terms of diagnosis and appropriateness of surgical treatment for an individual patient, but because they are the physicians ultimately responsible at surgery, they play an essential role in patient evaluation prior to surgery as well. They will assess whether patients are sufficiently healthy to undergo brain surgery. Hypertension, coagulopathies, chronic infections, and diabetes mellitus are just some of many comorbidities that do not preclude surgery but need to be dealt with or stabilized together with consulting physicians before neurosurgeons will proceed. During this preoperative visit, an important task for the neurosurgeon is to inform the patient of any possible adverse events. From a patient’s perspective, the interaction with the surgeon at this point also provides an opportunity to be fully apprised of the surgeon’s (and team’s) experience with the procedure.⁶ Although some patients may wisely inquire as to how many procedures the surgeon has performed, less assertive individuals may unknowingly contribute to the steepest part of the team’s learning curve. Arguably, surgeons should a priori disclose their record of experience with the procedure proposed.

Psychologist

We consider that the ideal team should have a dedicated movement disorders psychologist/psychiatrist for several reasons.15 Patients and their families are embarking on a stressful journey and may need mental support from the very start of the evaluation for surgery. In addition, just as patients need to be sufficiently healthy from a physical point of view, they also need to be of sufficient mental health to withstand the rigors of surgery. Thus psychologists will perform a battery of tests to confirm that patients are mentally stable, cognitively intact, and not depressed.¹⁶ They will also be able to assist in the detection of unrealistic expectations or inappropriate motivations for surgery.

Coordinator

Every surgery program needs a central and easily accessible person who can guide patients and their family members through all phases of the surgery process.¹⁷ This role is ideally assumed by a coordinator (physician assistant, nurse practitioner, or other qualified health professional) with responsibilities transcending departmental boundaries. Thus this dedicated coordinator’s tasks will include (1) coordinating the visits to individual team members and thereby minimizing inconvenience to patients and family members, (2) providing help with insurance and precertification issues, (3) educating the patient and family members and answering questions that remain after patients have seen the other team members, (4) taking an active role in the patient evaluation process, (5) and most of all, being a constant and visible presence throughout the entire process, providing a familiar personal contact for patients and their loved ones.

Intraoperative Period

Neurosurgeon and Neurologist

During surgery a team approach is crucial for optimizing outcome. Integrated teamwork is especially important when microelectrode recordings are an integral part of the procedure, as many (but not all) centers deem essential.^7,9,18,19 While the neurosurgeon directs the surgical planning and instrumentation, the neurologist/neurophysiologist interprets the recorded signals, examines the patient for motor and sensory responses, and evaluates the effects of macrostimulation to determine the physiological target. Together they decide on the final coordinates for DBS lead placement.

Coordinator

The presence of a trusted ally during a physically and mentally exhausting intervention could make the difference between a cooperative or a belligerent patient. Therefore, in an ideal situation the coordinator should be present in the operating room. The coordinator can also be invaluable as a scribe in the mapping process, and as a communication conduit between the operating room and the patient’s family in the waiting room in the case of prolonged procedures.

Postoperative Period

Neurologist and Coordinator

Following the immediate postoperative surgical care, the patient will be returning to the neurologist’s office to start the stimulation process. This time-consuming process consists of the initial programming visit and several adjustment visits over the following months.^20–23 Simultaneously, medications may be adjusted downward. Once the patient is on a steady stimulation regimen the neurologist should reevaluate the patient using the same standard assessments as before surgery.¹⁶ Proper determination of the benefit from surgery will aid in patient management and will also provide a “quality control instrument” for the surgical treatment. This formal assessment should be repeated over time to evaluate the long-term results of the procedure. It should be noted that even when the stimulation parameters and the medications are in optimal balance, DBS patients require more frequent attention from the neurologist for a variety of reasons. Initially, fear of the unknown will lead to frequent consultation. Later on, a variety of hardware-related problems can occur, including unexpected outages of the pulse generator due to unsuspected magnetic fields in the patient’s environment; discomfort due to the position of the connectors, the extension leads, or the pulse generators; infection, lead erosion, or battery failure. This requires careful and regular monitoring. Importantly, most patients also tend to indefinitely expect or at least hope that as yet untried parameter combinations can further increase the benefit from the stimulation. In addition, stimulation can be so effective that malfunction is perceived as a true emergency.²⁴ Consequently, a key feature in any stimulation program is that patients can be evaluated in the clinic on short notice. Having only one individual proficient in the management of DBS patients is therefore insufficient, and adequate training of the coordinator and other staff in performing stimulator evaluations and adjustments will enhance the efficiency of the team.

Psychologist

Following surgery, stressors on the patients and their families do not immediately subside and may require intervention by the psychologist. Sometimes unrealistic expectations exceed the outcome and, as a result, disappointment needs to be dealt with. In other instances surgery may have caused cognitive or behavioral changes threatening the status quo and disrupting the family’s routines.25,26 Although such changes are mostly transient, that fact is not known at the time they occur, and the psychologist can offer valuable support during the recuperation. Whether cognitive/behavioral changes did or did not occur, all patients should be routinely evaluated with the same neuropsychological test battery given preoperatively.¹⁶ This will not only establish that they indeed have fully recovered from surgery, but will also serve as a “quality control instrument” from a cognitive perspective for the procedure performed.

Selecting Disorders

As with ablative surgery in the past, numerous movement disorders can be and have been surgically addressed with DBS.13,27 However, DBS is currently only US Food and Drug Administration (FDA)-approved for three indications: Parkinson disease (PD), essential tremor (ET), and dystonia (the latter under the restrictions of a humanitarian device exemption). The collective experience with DBS in other movement disorders is too limited to identify specific patient selection criteria and is therefore not discussed here.

Parkinson Disease

Idiopathic PD is characterized by the presence of two or more cardinal features: rest tremor, rigidity, bradykinesia, and, with advanced disease, impaired postural reflexes. Symptoms initially respond favorably to dopaminergic medication, such as L-dopa. The efficacy of DBS of the globus pallidus internus (GPi) or subthalamic nucleus (STN) has now been demonstrated in several controlled studies.^28–30 PD has many imitators, which is one of the reasons a movement disorders specialist should evaluate potential surgical candidates. Especially early in the disease PD can be difficult to distinguish from parkinsonism caused by a variety of other disorders, such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), diffuse Lewy body disease, corticobasal ganglionic degeneration, vascular Parkinsonism, normal pressure hydrocephalus, and drug-induced parkinsonism. No data currently exist to support the use of DBS for any of these conditions; their presence therefore needs to be ruled out as part of the selection process.³¹ Some of these parkinsonian disorders can be deceivingly responsive to L-dopa, albeit usually for very limited periods of time. Thus, even in specialized movement disorders clinics 10% of cases diagnosed with PD during life may in fact receive a different diagnosis at autopsy. Mostly, however, time is sympathetic to this dilemma and the distinction between PD and other forms of parkinsonism becomes more defined with longer disease duration. This is an argument in favor of an often used rule of thumb that patients should have had PD for at least 5 years before surgery is considered.¹⁶ By that time the diagnosis of idiopathic PD can usually be made beyond reasonable doubt based on the asymmetric onset, the slowly progressive course, the excellent and maintained response to L-dopa, the maintained asymmetry, and the absence of stigmata of the aforementioned other parkinsonian disorders.

Essential Tremor

Classic ET is a monosymptomatic disorder characterized by postural or kinetic tremor (frequency 4 to 12 Hz) involving hands and forearms.^32,33 Rest tremor is absent, except in the most severe cases where the tremor persists even though the patient is seemingly at rest.³⁴ Head tremor may be an additional or even isolated feature, but only in the absence of abnormal head posturing.³⁵ Less frequently the tremor is also (but not in isolation) present in the voice, the trunk, the face, and the legs.³⁶ The remainder of the neurological exam is usually normal, although some patients may have some rigidity or postural instability.^5,36,37 ET is familial in 60% of cases with autosomal dominant transmission with incomplete penetrance. Patients report a beneficial effect from alcohol. With the passage of time, the frequency of ET decreases while the amplitude increases, leading to considerable disability, especially in those with a strong kinetic component.³⁸ The target of choice for DBS is the ventrointermedius nucleus of the thalamus (Vim), including its anterior border with the ventro-oralis posterior nucleus (Vop),³⁹ and possibly the subthalamic region.⁴⁰ The efficacy of DBS has now been demonstrated in several studies.^14,41,42 The differential diagnosis of ET includes cerebellar and Holmes tremor.³⁶ Cerebellar tremor is a lower frequency (< 5 Hz) kinetic tremor that is amplified during the last part of the movement trajectory (intention tremor). Depending on the etiology the tremor can be unilateral or bilateral. Common causes are MS, stroke, and trauma. Often the involuntary movement is an inseparable combination of cerebellar tremor and ataxia. The latter may contribute to the incomplete response to DBS (or lesioning) as reported for MS-associated tremor.⁴³ Holmes tremor (or rubral tremor) is a combination of rest and kinetic tremor (frequency < 4.5 Hz) due to midbrain lesions that involve the cerebellar outflow tract as well as the substantia nigra.^33,36 Case reports suggest that Holmes tremor responds to Vim DBS.^44,45 Another recent report suggests that dual electrodes, one in the cerebellar receiving area (Vim) and one in the pallidal receiving area [Ventro-oralis anterior (Voa) and posterior (Vop)] are a more definitive therapy.⁴⁶

Dystonia

Dystonia is a syndrome of involuntary, patterned, and repetitive contractions of opposing muscles leading to often painful twisting movements and abnormal postures.⁴⁷ Primary dystonia is not considered a degenerative disorder but rather one characterized by abnormal physiology at multiple levels along the neuraxis.48,49 Consistent with this concept, no pathological substrate has been found, making dystonia an attractive target for physiological manipulation with DBS. Several recent case series and a double-blind crossover study have now documented considerable benefit (50 to 90% improvement) of GPi DBS for patients with primary generalized dystonia (PGD).^50–53 The most common (30%) cause of PGD is a single GAG deletion mutation in the DYT1 gene.⁵⁴ The commercially available assay for this mutation has provided an opportunity to study this genetically homogeneous subgroup of dystonia patients. Secondary dystonia may be associated with a variety of neurological disorders, trauma, and other insults to the brain. Whether secondary dystonia is generalized or restricted to one side of the body (hemidystonia), the variable underlying etiology makes for a variable outcome of GPi DBS, with reported improvement ranging form 0 to 50%. It has been suggested that secondary dystonia may respond better to thalamic than to pallidal DBS.⁵¹ In a recent case series, on the other hand, dystonia caused by pantothenate-kinase-associated neurodegeneration (PKAN) demonstrated an excellent response to pallidal DBS.⁵⁵

Editor’s Comments

This chapter describes how a movement disorder specialist approaches the task of evaluating patients for surgery. Approximately a third of patients that present to a movement disorder center for DBS are not immediate candidates for surgery.⁸⁰ The rational for exclusion includes inadequate medical trial, insufficient disability, cognitive and/or psychiatric disorders, incorrect diagnosis, predominantly surgically unresponsive symptoms, and inability to tolerate surgery. The movement disorder neurologist is in the ideal position to initially screen patients so that only the appropriate patients go on to surgery. Surgical intervention for nonidiopathic PD syndromes is generally of little value and frequently results in increased neurological deficits.

Because there is no laboratory test to establish the diagnosis of PD, differentiating PD from MSA or PSP is the biggest challenge in selecting appropriate patients for surgery. MSA is a complex of sporadic neurodegenerative disorders that is usually manifest in the early sixth decade of life and progresses quickly, with a mean survival of approximately 9 years. However, there is some degree of variability in the rate of progression. Symptoms are symmetrical, bradykinetic-rigidity predominant, and may have a modest response to L-dopa. Red flags suggesting MSA include orofacial dystonia, axial dystonia (especially with lateral flexion), an irregular jerk postural tremor, early onset of dysarthria, early onset of gait abnormality, and multiple autonomic dysfunctions such as Raynaud phenomena, emotional instability, orthostatic hypotension, and neurogenic bladder. Classically, three MSA subgroups have been recognized: (1) striatonigral degeneration (SND), where extrapyramidal signs predominate and are therefore most likely confused with PD; (2) Shy-Drager syndrome (SDS), where autonomic failure is predominant; and (3) olivopontocerebellar atrophy (OPCA), where cerebellar signs are predominant. Others will be subtyped by the presence of predominant parkinsonian or cerebellar symptoms.⁸¹ Although a positron emission tomography (PET) scan can be useful in distinguishing MSA from PD, the problem is that there are very few third party payers who will actually reimburse this procedure.

PSP is the most common parkinson-plus neurodegenerative disease. There is early onset of gait disturbance and falls. PD gait disturbance occurs after prolonged duration of symptoms and then in only ~11% of patients. Other common symptoms early in PSP are nonspecific changes in personality, mental and physical slowness, irritability, and social withdrawal, which can sometimes be diagnosed as PD with depression. A minority of the patients actually present with gaze palsy, dysarthria, and dysphagia, and as such the presence of vertical gaze palsy may not always be a useful differential diagnostic tool. The PSP picture can be quite atypical early in the disease, and the addition of time becomes a helpful differential for the diagnosis.⁸²

It is extremely uncommon for patients to have idiopathic PD below the age of 21 (juvenile PD). Most parkinsonian symptoms at that age are the result of a multitude of other diseases with the rare exception of a few genetic forms.⁸³ More difficult to sort out are the manifestations of young-onset PD, which range from age 21 to age 40. These generally represent the lower end of the spectrum for PD and typical Lewy body pathology. Nevertheless, there can be some overlap, and again careful history and neurological examination should sort out most of the unusual cases. Nevertheless, anyone with an onset before the age of 50 should be suspect and a history of the diagnosis for at least 5 years should be present before any surgical intervention is considered.

In addition to the physical examination, no patient should have an evaluation completed until an MRI scan is performed. This will help to identify areas of atrophy that may provide some diagnostic help. In PSP, the patient may have particularly large atrophy of the cortex and midbrain. MSA frequently has marked atrophy of the pons in the olivo-pontocerebellar form, but not striatonigral degeneration. The presence of strokes may suggest a vascular parkinsonism. However, a mild to moderate degree of periventricular lucency and deep white matter changes are generally not a problem.⁸⁴ Severe cerebral atrophy, of course, is not only a technical problem for surgery but also may suggest an impending dementia, if it is not already present. The presence of enlarged ventricles is usually ex vacuo. Their presence on an MRI scan should be a sign that further investigation is necessary. Rarely is shunting effective, although occasionally, if there is true hydrocephalus, shunting may reduce some of the symptomatology. Corticobasal ganglionic degeneration is a degenerative combination of extrapyramidal and cerebral cortical dysfunction. This is a little more insidious than the previously described syndromes and this asymmetric akinetic-rigid syndrome, which is evident early on and can be confused with PD; however, the early onset of cortical sensory loss and apraxia with occasional alien limb phenomena suggests the differentiation from PD. MRI frequently demonstrates asymmetrical cerebral atrophy, especially in the frontal and parietal regions.

In addition to ensuring the proper diagnosis, medical treatment, and suitability for surgery, the movement disorder neurologist can also document the degree of disability with a standardized instrument that ensures the ability to gauge the effectiveness of surgery. These are United Parkinson Disease Rating Scale (UPDRS) and Core Assessment Program for Intracerebral Transplantation-PD (CAPIT-PD) for PD (www.movementdisorders.org & publications). These are very time-consuming and require significant expertise to perform properly. Similarly, the neuropsychologist can provide standardized tests of cognition and psyche. These are the gold standard to evaluate patients and will be performed in centers of excellence.

It is frequently advisable to have the neurosurgeon and neurologist have their clinics on the same day. That way, patients can be exchanged easily back and forth without having to reschedule. In addition, this allows the neurosurgeon the opportunity to see a patient more often in the off state than would otherwise be anticipated. Patients who come in for their off evaluations can frequently be very quickly examined by the neurosurgeon without disrupting the entire day. Certainly, in follow-up visits where the neurosurgeon is simply checking a wound whereas the neurologist will be evaluating medication and stimulation parameters, the one-stop approach satisfies patients. When additional surgery is needed, the ability to immediately contact the neurosurgeon is most useful. By clinical practice, the neurologist will have more clinic days and more clinic time than the neurosurgeon, but keeping the surgical patient appointments on the same day can be advantageous. It is also quite useful to cross train the neurology and neurosurgery physician extender so that there is redundancy in the system and a smooth therapeutic approach can be achieved even in the absence of one or two personnel due to vacations, illness, and so forth.

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