Surgical Management of Parkinsonism

Surgical Management of Parkinsonism Fifteen–Twenty High-Yield Points Rationale and patient selection

Surgery is considered when motor complications become refractory to best medical therapy — that is, disabling motor fluctuations or dyskinesia despite optimised levodopa and adjuncts.

The essential principle is that only levodopa-responsive symptoms improve after surgery. A good levodopa response is the single best predictor of surgical benefit; levodopa-unresponsive axial features, gait freezing, falls and dysautonomia do not improve.

Candidates must be cognitively intact. Dementia, active psychiatric illness (especially depression with suicidality) and severe comorbidity are limitations.

Diagnosis must be secure — Parkinson-plus syndromes respond poorly and are a contraindication. The Queen Square Brain Bank criteria should be satisfied.

Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) or globus pallidus interna (GPi) produces sustained improvement in motor function, especially in symptoms that respond to levodopa, and reduces drug-induced involuntary movements.

STN stimulation allows the greatest reduction in dopaminergic drug dose (typically 40–60%), which indirectly reduces dyskinesia; GPi stimulation has a more direct antidyskinetic effect and is often preferred where cognition or mood is fragile.

The ventral intermediate nucleus of the thalamus (VIM) is the target when tremor is the dominant and disabling symptom, including in essential tremor. It does not help bradykinesia or rigidity.

Mechanism: high-frequency stimulation functionally inhibits or desynchronises pathologically synchronised basal ganglia output, normalising the abnormal beta-band oscillations in the motor circuit.

The textbook position is that DBS is not currently used in elderly people with PD. However, recent observational studies found that efficacy in patients over 70 was similar to that in younger patients, and the incidence of adverse effects did not increase with age.

Long-term follow-up shows that disability continues to progress after DBS, probably because the underlying neurodegeneration continues — DBS is symptomatic, not disease-modifying.

Procedure-related: intracranial haemorrhage, stroke, seizure and infection at the implant site; these relate to the intracranial procedure itself.

Hardware-related: lead migration or fracture, extension wire erosion, device infection, and the need for battery replacement.

Stimulation-related: dysarthria, paraesthesiae, eyelid-opening apraxia, gait and balance deterioration, and weight gain.

Neuropsychiatric: there are long-standing concerns about long-term safety, with risks of depression and suicide, as well as apathy, impulsivity and, in vulnerable patients, cognitive decline.

Lesional surgery — thalamotomy, pallidotomy and subthalamotomy — preceded DBS and remains an option where DBS is unaffordable or follow-up is impractical. It is usually performed unilaterally, since bilateral lesions carry a high risk of dysarthria and cognitive decline.

Gamma knife radiosurgery and MR-guided focused ultrasound thalamotomy are incisionless alternatives, described in the textbook as options for severe medication-refractory tremor.

DBS is also used for other movement disorders in the elderly: essential tremor (VIM), refractory dystonia (particularly effective in primary dystonia), and occasionally tardive dyskinesia.

Continuous-infusion therapies (intrajejunal levodopa gel via PEG-J, apomorphine) are the main non-DBS device-aided alternatives for advanced disease and are relevant when DBS is contraindicated.

Rehabilitation must continue after surgery. Functional rehabilitation preserves motor function, and sessions are best timed to the peak effect of levodopa.

Multidisciplinary assessment before surgery must include a movement disorder neurologist, neurosurgeon, neuropsychologist and psychiatrist, with a formal levodopa challenge (150–250 mg in the fasting state, with assessment every 30 minutes for 2–3 hours).