Variable Frequency Stimulation of Subthalamic Nucleus for Freezing of Gait in Parkinson's Disease

HFS of STN provides consistent, long-term improvement of the cardinal motor signs of PD, such as bradykinesia, tremor and rigidity. FOG has responded poorly to HFS and tends to continue to deteriorate over time, but this can be alleviated by relatively LFS. Evidence has indicated that LFS-STN can improve axial signs in some but not all PD patients, but most of them experienced loss of efficacy in the short term. Then comes to the little improvement or even worse of tremor, rigidity and bradykinesia, which consists of the three main symptoms of Parkinson's disease. Thus even if axial problems could be solved by LFS in a long way, it could also be hard to tolerate by those patients. The effect of VFS on FOG will be studied. The investigators hypothesize that VFS could have better effect on Freezing of gait than HFS and LFS.

Inclusion criteria

• Patients were receiving bilateral STN stimulation for more than six months.
• They were optimized on conventional HFS for control of tremors, rigidity and bradykinesia yet complained of freezing of gait.
• Subjects had an ability to walk at least 10 meters independently during ON DBS condition.

Exclusion criteria

• gait disorders perceived by patients as a direct consequence of STN stimulation and not the primary disease.
• any change in the HFS DBS settings, three months prior to participation in the study.
• complete inability to walk despite assistance while DBS ON.
• Subjects responding to reprogramming of chronic DBS settings (report improvement of freezing).
• Subjects could not tolerate prolonged OFF medication condition.