Prior to enrolling a patient into a surgical program, it is generally recommended that patients are assessed by a neurologist with experience in movement disorders since it is essential to document that the patient does indeed have PD which cannot be medically managed. There have been a few case reports of the use of lesion surgery in the management of Parkinson-plus syndromes and the success rates are generally disappointing (23,24). Additionally, it is necessary to show that a patient has a good response to dopaminergic drugs since the antiparkinsonian benefit from levodopa correlates with the antiparkinsonian response to surgery (with the exception of tremor which may be more improved with surgery). Patients should receive appropriate trials of available medication before considering surgery. A levodopa challenge test, as described in the core assessment program for intracerebral transplantations (CAPIT) (25) or core assessment program for surgical interventional therapies in PD (CAPSIT-PD) (26), is an indicator of a patient's response to surgery (27).
Speech, swallowing, and gait disturbances are common in advanced PD. Although these symptoms are less likely to improve following surgery and indeed may deteriorate postoperatively, especially following bilateral procedures (28-31), they should be recognized as relative, and not absolute, contra-indications.
By the time of referral to a surgical program, most patients will have late stage disease, possibly with cognitive or active psychiatric symptoms. Patients with moderate or significant cognitive decline may have less benefit from surgery and may further decompensate postoperatively (24,32). It should be recognized by the patient, family, and carers that their benefit/risk ratio is lower than in a cognitively intact patient. Centers should obtain formal neuropsychometric testing prior to surgery and utilize these results in considering surgical candidacy.
Psychiatric symptoms (hypomania, depression, suicide, or impulse control disorders) can be aggravated or induced by functional neurosurgery (33). Patients referred for surgical consideration are usually referred in the knowledge that they have an absence of dementia or active psychiatric symptoms, and yet a recent review revealed that the presence of depression (60%), anxiety (40%), and psychosis (35%) with 23% of the 40 patients assessed requiring preoperative psychiatric management (34).
A magnetic resonance imaging (MRI) scan of the brain is essential to assess the normality of the target structures, degree of cortical atrophy, ventriculomegaly, and white matter changes. Patients are required to have a realistic expectation of the expected outcomes and limitations from functional neurosurgery. The assistance of a carer or a relative is desirable to aid with personal and emotional support and communication and the understanding of the risk benefit ratio. In 2006, in the United Kingdom, the National Institute for Health and Clinical Excellence (NICE) recommended that functional neurosurgery is performed in the setting of an experienced multidisciplinary team; overall, it was felt that stimulation surgery is preferable to lesion surgeries, but specifically that subthalamotomy should only be performed in the setting of special arrangements for consent, audit, and research (35). Recent comparative evidence supports this notion in indicating that generally bilateral ablative procedures carry more risk than unilateral ablative lesions and that stimulation surgery carries less side-effect risk than ablation (36).
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