Deep brain stimulation (DBS) of the bilateral subthalamic nucleus (STN) in Parkinson's disease is thought to produce adverse events such as emotional disorders, and in a recent study, we found fear recognition to be impaired as a result. These changes have been attributed to disturbance of the STN's limbic territory and would appear to confirm that the negative emotion recognition network passes through the STN. In addition, it is now widely acknowledged that damage to the orbitofrontal cortex (OFC), especially the right side, can result in impaired recognition of facial emotions (RFE). In this context, we hypothesized that this reduced recognition of fear is correlated with modifications in the cerebral glucose metabolism of the right OFC. The objective of the present study was first, to reinforce our previous results by demonstrating reduced fear recognition in our Parkinson's disease patient group following STN DBS and, second, to correlate these emotional performances with glucose metabolism using (18)FDG-PET. The (18)FDG-PET and RFE tasks were both performed by a cohort of 13 Parkinson's disease patients 3 months before and 3 months after surgery for STN DBS. As predicted, we observed a significant reduction in fear recognition following surgery and obtained a positive correlation between these neuropsychological results and changes in glucose metabolism, especially in the right OFC. These results confirm the role of the STN as a key basal ganglia structure in limbic circuits.
OBJECTIVE: To evaluate apathy and its relation to verbal fluency tasks in a consecutive series of 19 patients with Parkinson's disease (PD) submitted to deep brain stimulation of the subthalamic nucleus (DBS of STN).
METHODS: 19 consecutive PD patients submitted to bilateral DBS of STN were studied for apathy pre-operatively and 17 months after surgery. The PD patients underwent a battery of cognitive tests assessing reasoning, memory and frontal executive functions, including phonemic and categorial fluency tasks. The Beck Depression Inventory (BDI) was used for depression. Apathy was assessed by means of the Apathy Scale (AS). In order to quantify changes among individual patients, the clinical criterion of more or less than 1 SD (standard z-score) was used to register a patient as improved or worsened, respectively.
RESULTS: After surgery, apathy scores did not change and mood improved (p < 0.02), while a significant worsening was found in the phonemic fluency (p < 0.001). The percentage of patients with an apathy score above the recommended cut-off value (14) was 42% both before and after DBS of STN. Individual outcomes on the apathy scale (1 SD criterion) evidenced that 53% of the patients remained stable, 16% improved, while 31% worsened. This last percentage reduced to 21% (4/19) when considering only the PD patients with an apathy score > or =14 after surgery. No significant correlation was found between the apathy scores variation and any of the neurological variables considered, and, in particular, no correlation was found between apathy and verbal fluency.
CONCLUSIONS: The results of the present study suggest that DBS of STN does not necessarily induce apathy even if individual patients show a moderate post-operative worsening of apathetic symptoms.
