Combined STN/SNr-DBS for the Treatment of Refractory Gait Disorders in Parkinson's Disease

Combined STN/SNr-DBS for the Treatment of Refractory Gait Disorders in Parkinson's Disease: Design of a Two-armed Double-blind Cross-over Study

12 patients with idiopathic Parkinson's disease and refractory gait disturbances under best individual subthalamic nucleus stimulation and dopaminergic medication will be included into this randomised double-blind cross-over two-armed clinical trial. The treatment consists of two different stimulation settings using (i) conventional stimulation of the subthalamic nucleus [STNmono] and (ii) combined stimulation of distant electrode contacts located in the subthalamic nucleus and caudal border zone of STN and substantia nigra pars reticulata [STN+SNr].

A composite 'axial score' including the major clinical and anamnestic items on gait, posture and balance function from UPDRSII (items 13-15) and UPDRS III (items 27-31) constitutes the primary outcome measure. Secondary outcome measures include specified clinical and anamnestic assessments on freezing of gait, balance, quality of life, non-motor symptoms, impulsivity, impulse control and neuropsychiatric symptoms. The aim of the present trial is to investigate the efficacy and safety of combined stimulation on subthalamic and nigral electrode contacts [STN+SNr] in refractory hypokinetic gait disturbances compared with [STNmono] (active comparator). The results will clarify, whether the combined [STN+SNr] stimulation improves otherwise refractory gait disturbances in PD.

Inclusion Criteria:

• Written informed consent
• Age: between 18 and 80 years
• Idiopathic Parkinson's disease (according to the "British Brain Bank criteria" (Hughes, 1992) including genetic forms and therapy with STN-DBS (ACTIVA pulse generators) at least six months from surgery
• Optimized subthalamic stimulation at study enrolment (refer 'treatment' section)
• Gait disturbance refractory on best individual STN-DBS (STNmono) and dopaminergic therapy: 'gait score' in the best clinical [MedOn/STNmono] condition ≥ 12
• Clinical and image-guided (and facultatively electrophysiological) confirmation of (i) one of the two rostral contacts of the quadripolar electrode localized in the STN area, and (ii) the caudal contacts in the border zone of STN and SNr.
• Dopaminergic medication constant for at least four weeks prior to study enrolment
• Disease duration ≥ 5 years

Exclusion Criteria:

• Cognitive impairment (Mini Mental State Exam < 25)
• Participation in other clinical trials within the past three months and during enrolment in our study
• Suicidality, Psychosis
• Other severe pathological chronic condition that might confound treatment effects or interpretation of the data
• Pregnancy
• Acute adverse events from stimulation on contacts in the caudal STN / SNr border interfering with the intended stimulation protocol