From 100 consecutive patients approached, 96 patients completed the study. The four patients who declined to participate all cited the number of questionnaires as their reason for refusal. Demographic and disease characteristics of the sample are shown in . Of these 96 patients, 22 (22.9%) had previously undergone deep brain stimulation surgery in either the pallidum (GPi; 6%) or the subthalamic nucleus (STN; 17%), while 74 were exclusively medically managed. Approximately 42% of patients were taking a dopamine agonist when assessed. On average, patients were not demented or depressed. Only one patient scored below the cut-off for dementia (MMSE<24). Seventeen patients evidenced mild to moderate depression (BDI>14).
Demographics, disease characteristics, and group comparisons
According to responses on the EDDS, one patient met full diagnostic criteria for BED (1%). An additional 8 patients (8.3%) exhibited subthreshold binge eating in that they all met Criteria A and E for BED. Five patients did not meet Criterion B, 2 patients did not meet Criterion C, and 1 patient did not meet Criteria B, C, or D. This latter individual reported weekly episodes over the last 6 months.
The severity of disordered eating habits was quantified using EDE-Q global scores. In the entire sample, disordered eating correlated with general impulsiveness (r=.585; p<.001) and mania (r=.366; p<.001). No significant correlations were noted between disordered eating and any of the demographic, disease or psychological variables. shows that overeaters (N=9) did not differ from non-overeaters (N=87) on any demographic, motor or mood variables. However, overeaters endorsed greater amounts of overall disordered eating, impulsivity, mania, and clutter behaviors than non-overeaters.
Using psychometric criteria described by the individual scales’ developers, the prevalence of impulse control behaviors other than binge eating was determined. Note that DSM-IV clinical criteria were not used to categorize individuals, as a complete diagnostic interview for these other impulse controls disorders was not part of the present protocol. Six patients (6.25%) were identified as probable pathological gamblers. An additional 11 patients (11.5%) had problematic gambling. Eight patients (8.3%) had compulsive hoarding, 11 patients (11.5%) had compulsive buying, one patient (1.0%) had hypersexuality, and one patient (1.0%) had clinically-significant manic symptoms. No pathologic internet use, anorexia nervosa or bulimia nervosa was found.
Next, we examined whether overeaters were more likely than non-overeaters to demonstrate other impulse control behaviors. displays the number of overeaters and non-overeaters who met psychometric criteria in one or more of these domains. As shown, overeaters were more likely than non-overeaters to report mania, hoarding, hypersexuality, and compulsive buying. There was a trend for overeaters to be more likely than non-overeaters to exhibit significant obsessive-compulsive features. Six of the 9 overeaters (67%) met psychometric criteria for at least one other impulse control disorder, as compared to 25 out of 87 non-overeaters (29%). This difference was significant (χ2(1)=5.367; Phi=.236; p=.02).
Proportions of individuals meeting criteria for other impulsive control psychopathology
Four of the 9 (44%) overeaters were currently on an agonist, as compared to 41% of controls, and this difference was not significant (χ2(1)=0.03; Phi=.18; p=.86). Four out of 9 (44%) overeaters had undergone STN DBS surgery, and 0 had undergone GPi DBS. Twelve (14%) and 6 (7%) non-overeaters had undergone DBS in the STN and GPi, respectively. The association between overeating and DBS history (STN, GPi or no DBS) was at trend (χ2(2)=5.82; Cramer’s V=.246; p=.055).
In order to determine the relative contributions of demographic, disease and iatrogenic variables to overeating, a hierarchical logistic regression was conducted in which the dependent variable was eating status (overeater or non-overeater). Based on previous research, the first block comprised iatrogenic variables (DBS, DA agonist therapy, levodopa equivalent daily dose). The second block comprised disease characteristics (age of PD onset, UPDRS-III total score), and the third block comprised demographic characteristics (age, sex, education). Results are displayed in . While the model did not reach significance at any of the three steps, DBS emerged as the only independent predictor of being an overeater at all three steps (p=.023 after Step 1; p=.021 after Step 2; and p=.019 after Step 3).
Hierarchical logistic regression results