Cholinergic deficiency in the brain can be related to gait and balance problems in Parkinson disease (PD). Recent clinical trials suggested a beneficial role of acetylcholinesterase inhibitors (AchEI) on gait in PD. In this study, the investigators are planning to study the influence of AchEI on a brain network for gait and balance in PD. As gait problem is prominent in postural instability and gait disturbance (PIGD) subtype, this study will focus on the patients with PIGD phenotype.

PD patients with PIGD subtype will be included.

1. Assessment:

   • Overall features of PD are assessed by Unified Parkinson Disease Rating Scale (UPDRS). Non-motor features including cognition will be assessed by standard scales. Gait and balance will be assessed by gait analysis system, which measures physiological parameters of gait such as velocity, variability and center of pressure. Positron emission tomography using 18F-fluorodeoxyglucose (FDG PET) will be done to brain activities related to gait and balance.
   • Clinical evaluation will be done at the baseline, 4th, 8th and 12th week
   • Gait analysis and FDG PET will be done at the baseline and 12th week

2. Drug dosage

   • For the first 4 weeks, 5 mg/day
   • Then, 10 mg/day for 8 weeks

Inclusion Criteria:

• Parkinson disease diagnosed by United Kingdom Parkinson's disease Society Brain Bank Criteria
• Postural instability and gait disturbance phenotype
• Hoehn and Yahr stage ≤ 3
• Mini-Mental status examination ≥ 24

Exclusion Criteria:

• Significant motor complication affecting daily activities
• Drugs related to acetylcholine metabolism