The study included 61 patients with PD and 35 with dystonia, whose baseline characteristics are presented in . Among participants with PD, 30 had GPi and 31 had STN DBS, with a majority of PD participants being male (48M/ 13F). The PD patients’ average age was 61 years, and a follow-up weight obtained at an average of 38 months. Although PD subjects with GPi were heavier than those with STN on average (84 vs. 74 kg, p=0.0078), their baseline BMIs were only slightly higher (27 vs. 25 kg/m2, p=0.21) compared to those treated with STN, due to differences in height (1.77 vs. 1.71, p=0.06).
Baseline characteristics of subjects.
Among dystonia patients, 27 had GPi and 9 had STN DBS implants, with similar proportions of males and females (18M /18F). Those treated with GPi DBS were slightly younger on average (45 vs. 48 years, p=0.68) and had somewhat lower weight (72 vs. 84 kg, p=0.065) and BMI (24 vs. 28 kg/m2, p=0.065) compared to those with STN DBS, though none of these differences were statistically significant. In dystonia patients, the amount of time between the baseline and collection of post-operative data points was longer in the GPi DBS group than in the STN DBS group (27 vs. 18 months, p=0.023).
The distribution of annual change in BMI is presented in . The difference between targets in annual change in BMI was much larger for the dystonia patients than for the PD patients (target-by-disease interaction, p=0.012). Therefore, we stratified our analyses by disease and compared the two brain targets in both PD and dystonia separately ( and ).
Annual change in BMI after DBS surgery, stratified by disease and surgical target.
Median change in weight (kg) per year in DBS patients after surgery.
Median change in BMI per year in DBS patients after surgery.
Among those with PD, there was a non-statistically significant difference in median annual change in weight (0.93 kg/yr, p=0.071) but a statistically significant difference in change in BMI (0.53 kg/m2/yr, p=0.037) by target. Those treated with GPi DBS had a small, non-statistically significant decrease in weight (−0.04 kg/yr, 0%/yr, p=0.59) and BMI (−0.14 kg/m2/year, p=0.32), whilethose treated with STN had a trend towards anincrease in weight (+0.89 kg/yr, 1%/yr, p=0.079) and BMI (+0.39 kg/m2/year, p=0.055). Dystonia patients treated with STN DBS had a greater increase in weight (6.10 kg/yr, 7%/yr, p=0.028) and BMI (1.81 kg/m2/year, p=0.021), while those treated with GPi DBS showed only a small increase in weight (0.40 kg/yr, 1%/year, p=0.68) and BMI (0.14 kg/m2/year, p=0.56) with a statistically significant difference in median weight gain (median 5.70 kg/yr, p=0.027) and BMI increase (1.67 kg/m2/yr, p=0.020) found between the two targets. Of the GPi DBS dystonia patients, 16 had an increase in BMI (range: 0.01 – 3.82 BMI/yr) while 11 had a decrease in BMI (range: −0.04 – −1.47 BMI/yr). In the dystonia patients with STN DBS, 7 had an increase in BMI (range: 1.09 – 7.53 BMI/yr) and only 2 saw a decrease in BMI (range: −0.085 – −0.93). In the dystonia patients who received GPi DBS, 71% of those with generalized dystonia gained weight, while 15% of those with focal or segmental (craniocervical) dystonia gained weight. In dystonia patients with STN DBS, 100% of the generalized dystonia patients gained weight while 71% of the segmental (craniocervical) patients gained weight.
Multivariable median regression analyses, stratified by disease, were performed to control for potentially confounding factors (). Among those with PD, baseline BMI was negatively associated with annual change in BMI (−0.78 kg per baseline kg/m2/yr, p=.009), demonstrating that those with lower BMI at baseline were more likely to gain weight after surgery. There were no significant associations with other factors in the model (age, time to follow-up, gender, or change in LEDD (p=0.99)) in PD patients. STN target was associated with slightly greater weight gain compared with GPi target, although the difference between targets did not reach statistical significance (+3.09 kg, p=0.26). In the patients with dystonia, those treated with STN DBS gained a median of 7.99 kg more than those treated with GPi DBS (95%CI: 1.87 to 14.11, p=0.012). Baseline BMI in dystonia showed a trend toward a negative association with weight gain (−0.39 kg per pre-op BMI point, p=0.15), but the effect size was small and the association did not reach statistical significance. Dystonia patients also showed a trend toward more weight gain in women (2.03 kg more than men, p=0.38). Percent improvement in BFM-DRS showed a trend toward having a small positive relationship with annual change in BMI (0.034 kg per 1% improvement, 95%, CI: −0.025 to 0.094, p=0.25). Even with a reasonable clinical improvement of 50% in BFM-DRS after DBS, this would only give an effect size of 1.7 kg, which is still overshadowed by the effect size of target.
Results of median regression analyses for each disease with total weight change (kg) as the primary outcome.