PATIENT SELECTION

Diagnosis

• Deep Brain Stimulation (DBS) for confirmed idiopathic Parkinson's Disease (PD) pts

• Idiopathic PD: bradykinesia ± rigidity, resting tremor, postural instability

• Postural instability early in disease → potential atypical parkinsonism, relative DBS CI

• Atypical parkinsonian syndromes (PSP, MSA, Lewy body dementia, corticobasal ganglionic degeneration) can mimic idiopathic PD → avoid DBS, ↓ response to stimulation

• Atypical parkinsonism: early onset, rapid progress, early dysautonomia, bulbar dysfunction, respiratory compromise, spasticity, ataxia, apraxia

Disease Severity & Duration

• PD severity & duration ≠ DBS outcome predictors, but rule out atypical parkinsonism

• Advanced Sx < 5 yrs after onset → further ✓ for atypical parkinsonism

• DBS CI if severe motor complications → ↓ QOL

• Average PD duration b/w 11-14 yrs at DBS, but earlier DBS (7 yrs) shows promising results

• Severe PD disability typically aligns w/ UPDRS motor scores ~30 or MDS-UPDRS scores ~50

• Ideal DBS candidate: severe disability off levodopa, manages well on Rx ± dyskinesias

Levodopa Response

• Sustained preoperative levodopa response: ↑ diagnostic support for PD, best predictor of DBS outcome

• Levodopa response defined as ≥ 30% ↑ in UPDRS motor scores over "off" state

• Levodopa response beneficial even in levodopa intolerant PD pts or w/ dopa-refractory tremor

Age

• Advanced age (especially >70 yrs) can negatively influence DBS outcome (↑ cognitive decline, gait instability), but no specific age cutoff

• DBS decisions in elderly individualized considering disability level, Qx risks, life expectancy, motivation

Cognitive Status

• Preoperative dementia is a risk factor for cognitive decline post-DBS, especially in older pts and severe preoperative cognitive impairment

• PD cognitive decline: impaired executive fnx, visuospatial abnormalities, impaired memory, language deficits

Psychiatric Comorbidity

• Preoperative psychiatric evaluation may assess untreated depression, anxiety, dopaminergic dysregulation syndrome, medication-induced hypomania/mania, psychotic symptoms, suicide risk

• Postoperative depression reported in 1% to 25% pts, but preoperative depression assessment not always conducted

• Psychosis in PD usually visual hallucinations, delusions

• Postoperative suicide attempts and suicides reported in 0.5% to 2.9% of PD pts after DBS, but further study required

Contraindications for DBS in PD:

• Severe cognitive impairment (detectable w/ neuropsychological ✓) is DBS CI as it can worsen post-Qx & override motor impairment as main disability driver

• Marked cognitive dysfnx on MMSE or low score on Mattis Dementia Rating Scale diminishes DBS QOL benefit → relative CI to DBS in PD

  • ↑ motor fnx in severely demented pts can be dangerous due to ↑ risk of falls, potentially worsened by ↑ impulsivity caused by STN-DBS

• Age is a prognostic factor (DBS benefit ↓ in pts >65 yrs)

• Comorbidities (HTN, DM, need for anticoagulation) ↑ Qx risk; 

  • Age & HTN ↑ intraoperative hemorrhage rates in DBS

• Pts w/ poor axial scores on UPDRS III & severe postural instability unlikely to benefit from DBS

• Hypophonia, a levodopa-nonresponsive Sx, unlikely to improve with DBS; pts & families should be warned of potential worsening in voice strength post-Qx.

TARGET SELECTION FACTORS

Surgeon’s Experience:

• GPi: considered more challenging target due to greater anatomic variability.

Alternative Target: ViM

• Vim: 1st target for PD, only ↓ tremor, valuable in tremor-dominant PD.

• STN & GPi: preferred over VIM as they alleviate tremor + other motor Sx.

Unilat. vs Bilat. vs Staged DBS

• Unilateral implant: consider if sig. asymmetry in Sx, advanced age or preoperative cognitive deficits.

• Unilateral Qx: faster recovery, ↓ postoperative edema (limited to one hemisphere).

• Severe Sx side: treat first w/ unilateral implant, then other side if necessary.

• Unilateral STN-DBS: sig. ↑ motor fnx, ↓ cognitive performance aspects, less than bilateral DBS.

QX COMPLICATIONS

Early (up to 6 mos.)

• 7.5% had early (90 days) complications in a large review

  • Wound infx (3.6%), pneumonia (2.3%), hemorrhage (1.4%), PE (0.6%)

  • No ↑ in complications for pts >75 yrs old

• Symptomatic hemorrhage risk during MER-guided DBS: 0.5% - 2.2%

  • ↑ risk w/ HTN, MER

  • ↓ risk strategies: maintain BP < 90 mm Hg, proper hydration, trajectories avoiding blood vessels

• Hardware infx requiring additional Qx (up to 10% cases)

  • • Abrupt cessation of stimulation, prolonged antibiotic Rx, emotional & economic strain on pt and team

Late complications: 

• hardware erosion, lead frx, lead migration

  • Erosion prevention: countersinking bur hole technique, ↑ IPG pocket size rostrally-caudally, multilayered closure

  • Early erosion Dx → possible partial hardware explantation

• Lead frx: ~2% of PD pts

  • Stress relief loops, securing lead extension above occipital ridge w/ extra fascial stitch may ↓ frx risk

  • Deep subcutaneous tunneling in the neck may ↓ "bowstringing" and scarring → ↓ frx risk

• Malpositioned electrodes requiring Qx revision: 0.8% - 1.7% per lead

  • Small repositioning (~2 mm) towards motor territory center can ↑ efficacy of marginally placed lead.