Objective: We aimed to investigate the neuropsychological outcome six months after bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) in Parkison’s disease (PD) patients and whether total electrical energy delivered (TEED) could be responsible for neuropsychological alterations.

Background: STN-DBS is currently the treatment option for advanced PD refractory to medical therapy. While the motor benefits of the surgery is well established, consensus regarding long-term neuropsychological outcome continues to be debated.

Method: Our study involved 21 PD patients (10 female, mean [± SD] age 59 ± 7.07 years) undergoing bilateral STN-DBS. Cognitive functions were assessed in all patients before DBS surgery (T0) and 6 months after DBS implantation (T1) with the Montreal Cognitive Assessment (MoCA) [1] and Verbal phonemic [2] and semantic fluency test [3]. At T1, we recorded stimulation parameters, in order to estimate total electrical energy delivered to the STN.

Results: One-way repeated measures ANOVAs revealed a significant main effect of ‘Time’ on phonemic fluency (F[2,40] = 10.39; P < 0.001; η2 = 0.34) and semantic fluency (F[2,40] = 11.21; P < 0.001; η2 = 0.33). Bonferroni-corrected post-hoc tests showed that phonemic and semantic verbal fluency  worsened at T1 (Fonemic T0 vs T1: mean ± SD = 42.38 ± 10.85 vs. 36.33 ± 10.80; P = 0.001; Semantic: 48.14 ± 8.36 vs. 40.86 ± 9.41; P < 0.001). TEED did not differ significantly between the left and right STN at T1 (t(16) = 0.533; P = 0.601). We  found no significant correlations between cognitive performance and TEED Left (all P > 0.285), TEED Right (all P > 0.256), or TEED Laterality (all P > 0.111).

Conclusion: Our pilot study suggests that STN-DBS can be considered as a significant contribution to the treatment of severe PD, although it can induce language changes. Chronic stimulation has been proposed as underlying mechanisms, but we didn’t find a correlation with TEED. It is possible that these and other effects underlie the etiology of cognitive sequelae in DBS of the STN and that these factors, such as patient age, preoperative neuropsychological function, surgical trauma, electrode placement within subdivisions of STN, and natural history of PD interact in a complicated manner influencing the outcome.

References: [1] Santangelo, G., Siciliano, M., Pedone, R., Vitale, C., Falco, F., Bisogno, R., … & Trojano, L. (2015). Normative data for the Montreal Cognitive Assessment in an Italian population sample. Neurological Sciences, 36(4), 585-591.

[2] Carlesimo GA, Caltagirone C, Gainotti G, and the group for the standardization of the mental deterioration battery (1996) The Mental deterioration battery: normative data, diagnostic reliability and qualitative analyses of cognitive impairment. Eur Neurol 36:378–384.

[3] Costa, A., Bagoj, E., Monaco, M., Zabberoni, S., De Rosa, S., Papantonio, A. M., … & Carlesimo, G. A. (2014). Standardization and normative data obtained in the Italian population for a new verbal fluency instrument, the phonemic/semantic alternate fluency test. Neurological Sciences, 35(3), 365-372.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/evaluation-of-the-association-between-total-electrical-energy-delivered-teed-and-cognitive-function-six-months-after-dbs-in-patients-with-parkinsons-disease/