Long-term efficacy of subthalamic nucleus deep brain stimulation in focal motor seizures and implications for candidate selection

Focal motor seizures (FMS) are often unresectable because of motor risk. We aimed to evaluate the long-term effectiveness and safety of subthalamic nucleus deep brain stimulation (STN-DBS) in patients with FMS and to identify suitable candidate patients. We analyzed long-term outcomes in 22 patients with FMS treated with STN-DBS, classifying patients as responders (≥50% seizure reduction) or non-responders and relating outcomes to seizure-focus topography using focus-frequency maps and region-of-interest-based volumetrics. In a SEEG cohort of 13 patients with electrodes in the sensorimotor cortex and the STN, including 1 from the DBS cohort, we quantified changes in interictal spike (IIS) rates and broadband (0.5-90 Hz) power spectral density (PSD) across distinct sensorimotor subregions during 100-Hz STN stimulation. At final follow-up (mean 45 months), median seizure reduction was 55%, with 14/22 responders and six patients achieved >90% reduction, including one seizure-free. STN-DBS was well tolerated, with no surgical complications and one explant for infection. Responders' seizure foci clustered in a medial sensorimotor strip comprising the paracentral lobule (PCL), supplementary motor area (SMA) and trunk representations of the precentral and postcentral gyri, and greater involvement of the PCL and trunk areas correlated with better outcome. SEEG analyses showed a global reduction in broadband power but regionally selective suppression of epileptiform activity, confined to the PCL and SMA. Together, STN-DBS appears to be a safe, effective option for FMS, and patients whose seizure foci involve the medial sensorimotor strip may be potential candidates.