STN-DBS frequency effects on freezing of gait in advanced Parkinson disease

Background: Severe gait disturbances and freezing episodes (frequently resistant to optimal dopaminergic treatment) often appear in advanced Parkinson disease (PD). Even several years after initiation, high-frequency subthalamic nucleus deep brain stimulation (STN-DBS) is still very effective for controlling segmental symptoms. However, there are no long-term data on the management of gait disorders and freezing in STN-DBS. Objectives: To compare the effects of various STN-DBS parameters on freezing of gait and to determine whether such effects are more related to stimulation energy (usual voltages vs high voltages at 130 Hz) or frequency (130 Hz vs approximately half this frequency: 60 Hz). Methods: We blindly assessed STN- DBS parameters in 13 PD patients reporting severe gait disorders. We compared the effects on gait of two different voltages (the patient's usual voltage [median 3 volts] and a high voltage [median 3.7 volts]) and two different frequencies ( 60 and 130 Hz, while maintaining the same total energy delivered) vs "off-stimulation" conditions. Results: The number of freezing episodes was significantly lower at the 60-Hz "high voltage/ equivalent energy" and higher at the 130-Hz/high voltage than for "off stimulation." The slight improvement in the Unified Parkinson's Disease Rating Scale motor score observed (at 130 Hz) did not achieve statistical significance. Conclusions: Our results prompt consideration of a new strategy for two-stage subthalamic nucleus deep brain stimulation (STN- DBS) frequency optimization, with stimulation at 130 Hz and the usual voltage during the initial years of STN- DBS and then at 60 Hz at a high voltage in Parkinson disease patients who develop severe gait disorders.