Multi-parametric analysis assists in STN localization in Parkinson's patients

Background Initial subthalamic nucleus (STN) localization is based on MRI and an anatomical atlas and then refined intraoperatively using electrophysiological mapping with microelectrode recordings (IOA - intraoperative multi-unit activity) during deep brain stimulation (DBS) in Parkinson's disease (PD). IOA is time consuming and subjective. The purpose of this study was to assess the value of high frequency multi-unit background activity (MUA, frequency > 500 Hz), and local field potentials (LFP, frequency 5-500 Hz) in detection of the STN borders. Methods This was a retrospective, single center study. 18 leads in ten PD patients that underwent STN DBS surgery were evaluated. IOA, MUA and LFP have been compared in detection of the STN. IOA using single train spikes analysis have been used as a gold standard. Results Both LFP in beta range (20-35 Hz) and MUA increased as the microelectrode entered the STN and their increase correlated with dorsal/ventral STN borders. The differences (mean ± sd) were: between IOA and MUA of the dorsal/ventral border 0.20 ± 0.76/0.28 ± 0.30 mm; between IOA and LFP of the dorsal/ventral border 0.08 ± 0.94/0.05 ± 0.53 mm. Using Bland-Altman statistics, only 2 / 36 (5.6%) differences between IOA and MUA and also 2 / 36 differences between IOA and LFP (one for the dorsal border and one for the ventral border) were out of ± 1.96 SD line of measurement differences. Correlation between dorsal border/ventral border positions obtained by IOA and MUA was 0.86, p < 0.000005/0.97, p < 10^{- 11}; by IOA and LFP was 0.78, p < 0.00015/0.88, p < 0.000001. Conclusions Both MUA and LFP are characteristically elevated in the STN compared to neighboring structures. They may provide fast, real-time, objective and reliable markers of STN borders.