To date, few studies have utilized standardized measures to assess the neurobehavioral changes that can accompany deep brain stimulation (DBS) of the subthalamic nuclei (STN) for the treatment of Parkinson's disease (PD), yet behavioral changes are the most debated among practitioners. We evaluated behavior with the Frontal Systems Behavior Scale (FrSBe), which includes a large-scale normative sample for self- and collateral ratings and is particularly relevant to PD with subscales assessing Apathy, Disinhibition, and Executive Dysfunction. Data were collected from 16 (11 males) PD patients. All FrSBe subscale scores increased significantly when retrospective preoperative scores and current (postoperative) scores were compared. Self- and collateral FrSBe ratings were not significantly correlated with each other, though for both scores at least half of the group met criteria for a clinically significant level of symptoms postoperatively. No significant correlations were seen for collateral current FrSBE ratings with cognitive or motor variables. Higher self-ratings of behavior characteristic of apathy were related to higher self-ratings of depressive symptoms, and to a smaller decrease in antiparkinsonian medications following surgery. We propose that the standardized assessment of behavioral aspects of executive dysfunction adds information that is largely dissociable from the motor and cognitive assessment of function in PD patients undergoing STN DBS. In future, prospective standardized measurement of behavior may allow for better prediction of which patients will experience significant behavioral issues postoperatively.
Both Parkinson's disease (PD) and its treatment impact frontal–striatal systems, circuitry that is critical for behavioral regulation (Frank, Scheres, & Sherman, 2007). While deep brain stimulation (DBS) of the subthalamic nuclei (STN) is one of the most effective treatments for PD motor dysfunction (for review see Limousin & Martinez-Torres, 2008), it is thought to adversely affect behavior and executive function in some patients (for review see Voon, Kubu, Krack, Houeto, & Tröster, 2006). Although the behavioral effects of STN DBS are widely debated both in the literature (see for example Tröster, 2008 commentary) and among practitioners, only the cognitive impact of STN DBS has been well-studied using standardized measures. To date, few reports have utilized standardized measures to assess neurobehavioral changes despite a call for such measurement nearly a decade ago (Trépanier, Kumar, Lozano, Lang, & Saint-Cyr, 2000).
Previous reports of behavioral executive dysfunction issues following surgery have been largely descriptive. One publication reported results of a standardized measure for a small selected sample of patients (Saint-Cyr, Trépanier, Kumar, Lozano, & Lang, 2000). A recent paper (Smeding et al., 2006) administered the Dysexecutive Questionnaire (DEX; Wilson, Alderman, Burgess, Emslie, & Evans, 1996); however, normative data are not available for this measure. The prevalence of papers on cognitive outcomes of STN DBS and the absence of papers focused on standardized assessment of behavior is particularly notable given that cognitive and behavioral measures purported to tap executive functions are readily dissociable (e.g., Reid-Arndt, Nehl, & Hinkebein, 2007Shallice and Burgess, 1991 and Vriezen and Pigott, 2002). Indeed, success on a standardized measure of problem solving or mental flexibility may fail to capture real-world behavioral consequences of executive dysfunction. Given the potential impact of behavioral changes on the functioning of the individual, and consequently their family, reliable and valid assessment of behavior is critical.
The choice of behavioral measures is far narrower than the choice of cognitive measures of frontal system functioning. Of the behavioral measures, The Frontal Systems Behavior Scale (FrSBe; Grace & Malloy, 2001) stands out as particularly relevant to PD. The FrSBe consists of 46 items, each of which falls into one of three subscales: Apathy, Disinhibition, or Executive Dysfunction. Zgaljardic and colleagues have previously emphasized how well these subscales map onto the frontal–striatal circuitry relevant to PD (Zgaljardic, Borod, Foldi, & Mattis, 2003). Psychometrically, the FrSBe distinguishes itself from other measures with its large-scale normative sample for self- and family ratings and demonstrated validity for the assessment of behavior disturbances associated with damage to the frontal–subcortical circuits (Malloy & Grace, 2005). For these reasons we chose the FrSBe to provide quantitative assessment of post-operative behavioral functioning in PD patients who had undergone STN DBS surgery. Our primary objective was to explore the utility of the FrSBe in characterizing behavioral disturbance in this population. Secondly, we examined the relationship between FrSBe scores, mood, motor function, and cognitive measures. Finally, we sought to determine the relationship between self- and family reports of behavior.
