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Weight and body mass index in Parkinson's disease patients after deep brain stimulation surgery
Parkinsonism and Related Disorders 11 (2005) 247–252 www.elsevier.com/locate/parkreldis
Weight and body mass index in Parkinson’s disease patients after deep brain stimulation surgery Paul J. Tuitea,*, Robert E. Maxwellb, Sayeed Ikramuddinc, Catherine M. Kotzdd,e,f, Charles J. Billingtonde,g, Maggie A. Laseskia, Scott D. Thielena a
Department of Neurology, Fairview-University Medical Center and the University of Minnesota, PWB 12-146, MMC 295, 420 Delaware St SE, Minneapolis, MN 55455, USA b Department of Neurosurgery, Fairview-University Medical Center and the University of Minnesota, Minneapolis, MN, USA c Department of Surgery, Fairview-University Medical Center and the University of Minnesota, Minneapolis, MN, USA d Veterans Affairs Medical Center, Minneapolis, MN, USA e Minnesota Obesity Center, Minneapolis, MN, USA f Department of Food Science and Nutrition, University of Minnesota, St Paul and Minneapolis, MN, USA g Department of Medicine, University of Minnesota, St Paul and Minneapolis, MN, USA Received 14 November 2003; revised 29 December 2004; accepted 15 January 2005
Abstract A retrospective chart review characterizing changes in 17 male and 10 female Parkinson’s disease (PD) patients undergoing deep brain stimulation (DBS) surgery indicated that 6 mo before surgery, patients lost a mean of 5.1 lbs, whereas in the 6 mo after surgery, subjects gained a mean of 10.1 lbs; 22% gained more than 14 lbs. In 10 patients followed an additional 6 mo, weight gain continued. This weight gain may be associated with decreased energy expenditure due to subsidence of chronic tremor. The magnitude of gain underscores the need for proactive management of body weight in PD patients undergoing DBS. q 2005 Elsevier Ltd. All rights reserved. Keywords: Parkinson’s disease; Deep brain stimulation; Weight; Obesity
1. Introduction Parkinson’s disease (PD) is a progressive neurodegenerative disorder. The treatment of PD has evolved over the years but primarily has included a variety of symptomatic medications. Functional neurosurgery, particularly deep brain stimulation (DBS), is a relatively new and effective treatment strategy for patients with advanced PD. DBS has been shown to improve quality of life [1], decrease medication requirements [2,3] and decrease rigidity, tremor, and bradykinesia [4–6] in these patients. Apart from its therapeutic effects on PD symptoms, DBS also appears to induce weight gain. PD patients tend to lose weight over the course of the disease [7] in spite of * Corresponding author. Tel.: C1 612 625 8685; fax: C1 612 625 7950. E-mail address: [email protected] (P.J. Tuite).
1353-8020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.parkreldis.2005.01.006
increased caloric intake [8]. This loss in body weight appears to be related to increased energy expenditure due to increased resting metabolic rate and persistent tremors, [9–12] although one study reported lower daily energy expenditure in PD patients relative to healthy elderly controls [13]. Weight gain has been reported in PD patients after both DBS [2,14,15] and pallidotomy [15–18]. Weight gain after DBS does not appear to be the result of reduced dysphagia, improved feeding, increased appetite, or lessened nausea/anorexia from reduced medication exposure [16]. Weight gain has been shown to correlate with improved United Parkinson’s Disease Rating Score (UPDRS) ‘on’ and ‘off’ motor scores [14,15,18], leading to the suggestion that it results from changes in the primary manifestations of the disease process [18] (i.e. reduced energy expenditures due to less frequent or severe dyskinesias) [14,15]. The repeated observation of weight gain after DBS suggests that clinicians need to proactively monitor weight changes in these patients.
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P.J. Tuite et al. / Parkinsonism and Related Disorders 11 (2005) 247–252
In the outpatient setting, body weight is used to monitor health and to analyze health risks [19]. Weight is easy to measure and both clinicians and patients have good reference data for which to evaluate changes in weight. Body mass index (BMI) is less commonly used and less well evaluated by clinicians and patients. BMI is a weight-toheight ratio that can be used to compare people in a population. BMI values can be correlated with body types, with higher BMI values reflective of greater obesity. These values are used for weight loss planning and to determine eligibility for weight loss surgery. Bariatric weight loss surgery is considered for those with a BMI greater than 35 kg/m2 who fail to lose weight from normal weight loss strategies that include medication, dietary counseling, and exercise. Although the normal range of BMI values is 18.5– 25 kg/m2, the BMI of the average American is 26.5 kg/m2 [20]. In Minnesota, where this study was conducted, the average BMI is 26.4 kg/m2 [20]. In our DBS program the BMI of patients on the day of surgery (mean BMIZ 26.6 kg/m2) is consistent with local and national averages of the average adult population. However, this value is higher than expected, given the weight loss that normally occurs over the course of PD. With the likelihood that patients with PD, many of whom are already overweight, will gain weight after surgery, it is important to understand the nature and course of weight changes and to attempt to identify individual differences that might predict weight gain. To begin to address this question, we retrospectively examined pre- and post-operative weights and BMIs of patients undergoing STN DBS at our institution.
If multiple implantation dates were recorded for a single patient, only the pre- and post-operative weight data from the first series of implant procedures were included in the analysis. Patients who received a stimulator later than 3/1/03 were excluded from the study because insufficient follow-up data were available. This study was approved by the Institutional Review Board at the University of Minnesota.
3. Data collection and analysis Weight and height information were collected by retrospective chart review. Data were collected for the 6 mo prior to and 6 mo following surgery. Data for the post-surgical period were further divided in an effort to distinguish the interval between device placement and stimulator activation (i.e. when weight changes might be considered surgicallyinduced) from the time period following stimulator activation (i.e. when weight changes might be considered stimulator-induced). The first interval was 0–1.5 mo, and the second was 1.6–6 mos. Mean weights for each individual subject were calculated for each of the defined time periods of (0–6 mo preoperatively, 0–1.5 mo post-operatively and 1.6–6 mo post-operatively). Weight on the morning of surgery was used as the index weight for comparison to the pre and postoperative values. BMI values for each individual subject were calculated for all time periods using the following formula: BMI Z Weight ðKgÞ Height2 ðm2 Þ
2. Methods 2.1. Subjects All patients who underwent STN DBS in the FairviewUniversity Medical Center and University of Minnesota surgical program from 1996 to 2003 were eligible for inclusion in the study. Inclusion criteria included complete weight and height data in the medical record for the study period and successful bilateral implantation of the Activa’ stimulator (Medtronic Inc, Minneapolis, MN) for 6 mo. The criteria for STN DBS surgery at our institution requires that a patient pass a neuropsychological examination, they have at least a 30% difference in the ‘off’ and ‘on’ medication state, they are dopamine responsive, and are assessed to be healthy enough to tolerate the surgery. In addition, all patients experienced some wearing off of medication effects prior to being considered for surgery. Some of the patients were tremor dominant but most had rigidity or disabling dyskinesia. All of the bilateral implantation procedures were simultaneously staged between 3 days and 2 weeks from the initial implant surgery.
A full data set was created that represented all patients with data from relevant time points. Mean weights and BMI were calculated and the time block averages were analyzed by repeated measures ANOVA followed by paired t-tests (Statview, Cary, NC) to compare means. Data from 12 mo after surgery were available for a subset of patients (NZ10). A separate analysis was conducted on 12-mo pre- and post-surgical data for these patients to determine if weight and BMI trends were consistent with that of the larger study group.
4. Results 4.1. Subject characteristics During the study period, 42 patients had successful implantation of a DBS STN stimulator. Twenty-seven subjects met the inclusion criteria. The average age of the subjects was 64-yr-old; 17 were male and 10 female. Thirteen patients were excluded from the analysis due to incomplete height or weight data in the medical record.
P.J. Tuite et al. / Parkinsonism and Related Disorders 11 (2005) 247–252
Four of these patients had STN DBS surgery in the last 6 mo of the study period and follow-up data was not yet available. Two patients received only unilateral stimulation during the study period and were excluded. There were no differences between the included and excluded patients in terms of age, pre-operative BMI, or pre-operative weight based on available data. Two patients had leads explanted and reimplanted during the 6-yr study period. The second implantations did not fall within the first post-operative time frame and the patient’s data was included in the analysis. Three patients had one of the two original leads explanted 5–12 mo later because of infection; the unilateral lead remained in place and functioning and the patient’s data were included.
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4.2.2. Subset of patients The subset of patients (nZ10) for whom 1 yr of pre- and post-operative weight and height data was available is depicted in Fig. 2. The data shows that this subset of patients had a statistically insignificant average weight loss of 6.2 lbs in the 12 mo pre-operative period (F1,9Z2.4, PZ0.1533) and a statistically significant weight gain after stimulation of 20.8 lbs (F1,9Z37.7, PZ0.0002). This smaller subset showed a gain of 9.6 lbs in the first 6 mo after surgery and a gain of 11.2 lbs in the subsequent 6 mos. This finding is consistent with the averages in the larger group of subjects studied over 6 mo and shows that the weight continues to rise for at least 12 mo after lead implantation. 4.3. BMI
4.2. Body weight 4.2.1. All subjects The average weight loss over 6 mo pre-operatively was 5.1 lbs (F1,26Z6.6, PZ0.0163), whereas the average weight gain 6 mo after lead implantation surgery was 10.0 lbs (F1,26Z20.8, PZ0.0001, Fig. 1). Stratification of weight gains post-operatively revealed no significant weight gain in the immediate post-operative period of 0–1.5 mo (F1,26Z 2.4, PZ0.1352), but a significant increase in weight from 1.5 to 6 mo after surgery, after stimulation was initiated (F1,26Z20.7, PZ0.0001). Six of the study patients gained in excess of 14 lb in the 6-mo post-operative period. Four of these patients were male and two female. The average age of these subjects was 60-yr-old. Examination of the average weight changes revealed that more subjects (nZ22) gained than lost weight (nZ5). Patients who lost weight had higher BMI on the day of surgery than those who gained weight (mean BMI of 30.4 vs. 25.7 kg/m2, respectively).
The average pre- and post-operative BMI changes (Table 1) in all patients and the subset for which 12 mo data were available paralleled weight changes. With all patients included, statistically significant BMI changes included an average BMI loss in the pre-operative period of 0.7 kg/m2 (F1,26Z6.4, PZ0.0178) and an average post-operative gain of 1.4 kg/m2 (F1,26Z20.1, PZ0.0001). There was no significant change in BMI during the first postoperative period (0–1.5 mo, F1,26Z2.2, PZ0.1503); all post-surgical gain occurred after the stimulator was activated. The average BMI on the day of surgery was 26.6 kg/m2. On the day of surgery, three subjects were underweight, nine were normal weight, eight were overweight, four were obese, and three were morbidly obese. In the subset for which 12 mo data were available, BMI was decreased by 0.9 kg/min2 in the pre-operative period (Table 1). This decrease is similar to that observed in the larger group, but significance was likely not reached because of limited power in the analysis resulting form low numbers.
Fig. 1. Six-mo pre- and post-surgical weights for all subjects (NZ27). Data shown are meanGstandard error. Data shown are meanGstandard error. *PZ0.0163 as compared to mean body weight in the K6 to 0 time period; ‡PZ0.0001 as compared to mean body weight on day of surgery.
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Fig. 2. Pre- and post-surgical weights for a subset of subjects in which data for the 12-mo pre- and post-STN DBS time-period was available (NZ10). Data shown are meanGstandard error. *PZ0.0002 as compared to mean body weight on day of surgery.
Like the larger group, there was no significant change in BMI in the 0–1.5 mo post-operative period (PZ0.9612, Table 1). In the 1.5–6 and 6–12 mo post-operative period, BMI was significantly increased by 1.4 kg/m2 (PZ0.0150, Table 1) and 1.8 kg/m2 (PZ0.0394), respectively, which resulted in a cumulative increase in BMI of 3.2 kg/m2 postoperatively in this group (PZ0.0001, Table 1).
5. Discussion Weight gain has been reported after functional neurosurgery for the treatment of PD. While on average the weight gain has been shown to be modest, previous research has been limited by small sample sizes and lack of preoperative data. This retrospective chart review was meant to replicate and extend the findings of previous studies. Our findings support previous research in documenting weight gain after DBS STN surgery. Our patients gained an average of 10.1 lbs in the first 6 mo after STN DBS (all included subjects) and an average of 20.3 lbs over 12 mo (smaller subset of included patients with 12 mo data available). Our 6-mo data are consistent with other reports in the literature [14,17,18] but our 12-mo data reveal much larger weight gain than has previously been reported. Importantly, in our patients, the slope of the mean weight gain appears to remain unchanged during the entire 12-mo post-operative
period, suggesting that weight gain likely continues beyond 1 yr after surgery. The present study also extends previous findings in evaluating not only weight but also BMI. The average BMI data in the pre-operative period (26.6 kg/m2) demonstrated that over 50% of our patients receiving STN DBS were overweight. The BMI values of the subjects in this study are surprising given the typical assumption that disease progression itself reduces weight and/or BMI in surgical PD patients. Indeed, an Italian study reported a preoperative mean BMI of 21.6 kg/m2 in their surgical subjects [14]. The discrepancy between our findings and those in the Italian study cannot be explained by cultural differences alone, since BMIs among healthy individuals are similar in the US and Italy. Three people in our study group were morbidly obese at the time of lead implantation. The fairly reliable finding that DBS results in weight gain in a majority of patients raises an important clinical question: should morbidly obese patients receive bariatric surgery prior to STN DBS, or should decisions about bariatric procedures be delayed until the extent of post-surgical weight gain can be appreciated? Furthermore, given that the exact mechanism of weight gain following STN DBS is unknown, is it prudent to even consider surgical weight loss intervention? The time course data presented in this study also raise the question of when, during the post-surgical period, decisions about weight
Table 1 BMI (kg/m2) changes Months pre-operative K12 to K6 All patients (NZ27) Subset (NZ10) *
No data 26.9G2.2
Surgery K6 to 0 27.3G1.4 26.4G2.2
Months post-operative
0
0–1.5 *
26.6G1.4 26.0G2.3
26.8G1.4 26.1G2.2
1.5–6
6–12 †
28.0G1.3 27.4G2.0†
P!0.02 as compared to mean body weight in the pre-surgery time period; †P!0.02 as compared to mean body weight on day of surgery.
No data 29.2G2.3†
P.J. Tuite et al. / Parkinsonism and Related Disorders 11 (2005) 247–252
management strategies (with or without surgery) should be made. At present, there are no outcome data in PD patients with respect to bariatric surgery. Twenty-two percent of the study patients (nZ6) gained more than 14 pounds in the post-operative period. There were no obvious pre-operative characteristics that distinguished these patients from the other patients in our limited sample. Further research with more systematic attention to pre- and post-operative variables as they relate to weight gain is urgently needed so that patient risk can be assessed as part of the decision about whether to recommend DBS. As part of this assessment, it may be worthwhile to consider the possibility that for some patients, weight gain after DBS may be a homeostatic response to disease-related weight loss, unique to a given patient. Nevertheless, even a small weight gain may result in functional disability in a patient who is already de-conditioned from long-standing PD. In consideration of the findings of this study and previous research, it would be prudent to monitor the DBS population carefully with periodic weighing and BMI calculations to identify those patients gaining excessive weight in the postoperative period and to make treatment recommendations early. A comprehensive assessment of those in the overweight, obese and morbidly obese categories should be completed with particular attention to medical co-morbidities, medications, diet, exercise and activity levels [20–22]. Referral to a dietician may be appropriate for assessment and counseling. In morbidly obese and obese patients, it is recommended that the patient be referred to a center with experience in surgical and non-surgical approaches to weight management [21,23]. It is important to recognize, however, that weight loss strategies that may be appropriate for the general population (i.e. aerobic exercise) may not be appropriate in the DBS population because of the loss of function that may accompany PD. Similar attention must be given to those patients in an underweight BMI category to ensure adequate nutritional status before and after surgery. Dysphagia and difficulty with feeding due to motor difficulties may be potential causes of a low weight and BMI. A dietician may be able to recommend higher energy foods that can be tailored to the patient’s motor impairment or dysphagia status. In severe cases, total parenteral nutrition or feedings via percutaneous endoscopic gastrostomy (PEG) tubes are warranted [24,25]. Potential limitations of this study include the reliance on retrospective data and the lack of control for post-operative or pre-operative factors that could influence weight changes. Future research could be directed at prospectively identifying pre-operative patient characteristics predictive of weight gain after STN DBS. In addition, the use of bariatric weight loss surgery in this population needs further exploration. Finally, conclusive research to elucidate the mechanism of weight gain after STN DBS would significantly advance the development of directed treatment strategies to manage weight gains.
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Acknowledgements The authors would like to thank Shilpa Seshadri, MS and Lisa Brauer, PhD for their help and expertise in the preparation of this manuscript.
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[19] Wilson PW, D’Agostino RB, Sullivan L, Parise H, Kannel WB. Overweight and obesity as determinants of cardiovascular risk: the Framingham experience. Arch Intern Med 2002;162(16):1867–72. [20] Mokdad AH, Ford ES, Bowman BA, Dietz WH, Vinicor F, Bales VS, Marks JS. Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. JAMA 2003;289(1):76–9. [21] Mellin L, Croughan-Minihane M, Dickey L. The solution method: 2-year trends in weight, blood pressure, exercise, depression, and functioning of adults trained in development skills. J Am Diet Assoc 1997;97(10):1133–8.
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Weight and body mass index in Parkinson’s disease patients after deep brain stimulation surgery Paul J. Tuitea,*, Robert E. Maxwellb, Sayeed Ikramuddinc, Catherine M. Kotzdd,e,f, Charles J. Billingtonde,g, Maggie A. Laseskia, Scott D. Thielena a
Department of Neurology, Fairview-University Medical Center and the University of Minnesota, PWB 12-146, MMC 295, 420 Delaware St SE, Minneapolis, MN 55455, USA b Department of Neurosurgery, Fairview-University Medical Center and the University of Minnesota, Minneapolis, MN, USA c Department of Surgery, Fairview-University Medical Center and the University of Minnesota, Minneapolis, MN, USA d Veterans Affairs Medical Center, Minneapolis, MN, USA e Minnesota Obesity Center, Minneapolis, MN, USA f Department of Food Science and Nutrition, University of Minnesota, St Paul and Minneapolis, MN, USA g Department of Medicine, University of Minnesota, St Paul and Minneapolis, MN, USA Received 14 November 2003; revised 29 December 2004; accepted 15 January 2005
Abstract A retrospective chart review characterizing changes in 17 male and 10 female Parkinson’s disease (PD) patients undergoing deep brain stimulation (DBS) surgery indicated that 6 mo before surgery, patients lost a mean of 5.1 lbs, whereas in the 6 mo after surgery, subjects gained a mean of 10.1 lbs; 22% gained more than 14 lbs. In 10 patients followed an additional 6 mo, weight gain continued. This weight gain may be associated with decreased energy expenditure due to subsidence of chronic tremor. The magnitude of gain underscores the need for proactive management of body weight in PD patients undergoing DBS. q 2005 Elsevier Ltd. All rights reserved. Keywords: Parkinson’s disease; Deep brain stimulation; Weight; Obesity
1. Introduction Parkinson’s disease (PD) is a progressive neurodegenerative disorder. The treatment of PD has evolved over the years but primarily has included a variety of symptomatic medications. Functional neurosurgery, particularly deep brain stimulation (DBS), is a relatively new and effective treatment strategy for patients with advanced PD. DBS has been shown to improve quality of life [1], decrease medication requirements [2,3] and decrease rigidity, tremor, and bradykinesia [4–6] in these patients. Apart from its therapeutic effects on PD symptoms, DBS also appears to induce weight gain. PD patients tend to lose weight over the course of the disease [7] in spite of * Corresponding author. Tel.: C1 612 625 8685; fax: C1 612 625 7950. E-mail address: [email protected] (P.J. Tuite).
1353-8020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.parkreldis.2005.01.006
increased caloric intake [8]. This loss in body weight appears to be related to increased energy expenditure due to increased resting metabolic rate and persistent tremors, [9–12] although one study reported lower daily energy expenditure in PD patients relative to healthy elderly controls [13]. Weight gain has been reported in PD patients after both DBS [2,14,15] and pallidotomy [15–18]. Weight gain after DBS does not appear to be the result of reduced dysphagia, improved feeding, increased appetite, or lessened nausea/anorexia from reduced medication exposure [16]. Weight gain has been shown to correlate with improved United Parkinson’s Disease Rating Score (UPDRS) ‘on’ and ‘off’ motor scores [14,15,18], leading to the suggestion that it results from changes in the primary manifestations of the disease process [18] (i.e. reduced energy expenditures due to less frequent or severe dyskinesias) [14,15]. The repeated observation of weight gain after DBS suggests that clinicians need to proactively monitor weight changes in these patients.
248
P.J. Tuite et al. / Parkinsonism and Related Disorders 11 (2005) 247–252
In the outpatient setting, body weight is used to monitor health and to analyze health risks [19]. Weight is easy to measure and both clinicians and patients have good reference data for which to evaluate changes in weight. Body mass index (BMI) is less commonly used and less well evaluated by clinicians and patients. BMI is a weight-toheight ratio that can be used to compare people in a population. BMI values can be correlated with body types, with higher BMI values reflective of greater obesity. These values are used for weight loss planning and to determine eligibility for weight loss surgery. Bariatric weight loss surgery is considered for those with a BMI greater than 35 kg/m2 who fail to lose weight from normal weight loss strategies that include medication, dietary counseling, and exercise. Although the normal range of BMI values is 18.5– 25 kg/m2, the BMI of the average American is 26.5 kg/m2 [20]. In Minnesota, where this study was conducted, the average BMI is 26.4 kg/m2 [20]. In our DBS program the BMI of patients on the day of surgery (mean BMIZ 26.6 kg/m2) is consistent with local and national averages of the average adult population. However, this value is higher than expected, given the weight loss that normally occurs over the course of PD. With the likelihood that patients with PD, many of whom are already overweight, will gain weight after surgery, it is important to understand the nature and course of weight changes and to attempt to identify individual differences that might predict weight gain. To begin to address this question, we retrospectively examined pre- and post-operative weights and BMIs of patients undergoing STN DBS at our institution.
If multiple implantation dates were recorded for a single patient, only the pre- and post-operative weight data from the first series of implant procedures were included in the analysis. Patients who received a stimulator later than 3/1/03 were excluded from the study because insufficient follow-up data were available. This study was approved by the Institutional Review Board at the University of Minnesota.
3. Data collection and analysis Weight and height information were collected by retrospective chart review. Data were collected for the 6 mo prior to and 6 mo following surgery. Data for the post-surgical period were further divided in an effort to distinguish the interval between device placement and stimulator activation (i.e. when weight changes might be considered surgicallyinduced) from the time period following stimulator activation (i.e. when weight changes might be considered stimulator-induced). The first interval was 0–1.5 mo, and the second was 1.6–6 mos. Mean weights for each individual subject were calculated for each of the defined time periods of (0–6 mo preoperatively, 0–1.5 mo post-operatively and 1.6–6 mo post-operatively). Weight on the morning of surgery was used as the index weight for comparison to the pre and postoperative values. BMI values for each individual subject were calculated for all time periods using the following formula: BMI Z Weight ðKgÞ Height2 ðm2 Þ
2. Methods 2.1. Subjects All patients who underwent STN DBS in the FairviewUniversity Medical Center and University of Minnesota surgical program from 1996 to 2003 were eligible for inclusion in the study. Inclusion criteria included complete weight and height data in the medical record for the study period and successful bilateral implantation of the Activa’ stimulator (Medtronic Inc, Minneapolis, MN) for 6 mo. The criteria for STN DBS surgery at our institution requires that a patient pass a neuropsychological examination, they have at least a 30% difference in the ‘off’ and ‘on’ medication state, they are dopamine responsive, and are assessed to be healthy enough to tolerate the surgery. In addition, all patients experienced some wearing off of medication effects prior to being considered for surgery. Some of the patients were tremor dominant but most had rigidity or disabling dyskinesia. All of the bilateral implantation procedures were simultaneously staged between 3 days and 2 weeks from the initial implant surgery.
A full data set was created that represented all patients with data from relevant time points. Mean weights and BMI were calculated and the time block averages were analyzed by repeated measures ANOVA followed by paired t-tests (Statview, Cary, NC) to compare means. Data from 12 mo after surgery were available for a subset of patients (NZ10). A separate analysis was conducted on 12-mo pre- and post-surgical data for these patients to determine if weight and BMI trends were consistent with that of the larger study group.
4. Results 4.1. Subject characteristics During the study period, 42 patients had successful implantation of a DBS STN stimulator. Twenty-seven subjects met the inclusion criteria. The average age of the subjects was 64-yr-old; 17 were male and 10 female. Thirteen patients were excluded from the analysis due to incomplete height or weight data in the medical record.
P.J. Tuite et al. / Parkinsonism and Related Disorders 11 (2005) 247–252
Four of these patients had STN DBS surgery in the last 6 mo of the study period and follow-up data was not yet available. Two patients received only unilateral stimulation during the study period and were excluded. There were no differences between the included and excluded patients in terms of age, pre-operative BMI, or pre-operative weight based on available data. Two patients had leads explanted and reimplanted during the 6-yr study period. The second implantations did not fall within the first post-operative time frame and the patient’s data was included in the analysis. Three patients had one of the two original leads explanted 5–12 mo later because of infection; the unilateral lead remained in place and functioning and the patient’s data were included.
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4.2.2. Subset of patients The subset of patients (nZ10) for whom 1 yr of pre- and post-operative weight and height data was available is depicted in Fig. 2. The data shows that this subset of patients had a statistically insignificant average weight loss of 6.2 lbs in the 12 mo pre-operative period (F1,9Z2.4, PZ0.1533) and a statistically significant weight gain after stimulation of 20.8 lbs (F1,9Z37.7, PZ0.0002). This smaller subset showed a gain of 9.6 lbs in the first 6 mo after surgery and a gain of 11.2 lbs in the subsequent 6 mos. This finding is consistent with the averages in the larger group of subjects studied over 6 mo and shows that the weight continues to rise for at least 12 mo after lead implantation. 4.3. BMI
4.2. Body weight 4.2.1. All subjects The average weight loss over 6 mo pre-operatively was 5.1 lbs (F1,26Z6.6, PZ0.0163), whereas the average weight gain 6 mo after lead implantation surgery was 10.0 lbs (F1,26Z20.8, PZ0.0001, Fig. 1). Stratification of weight gains post-operatively revealed no significant weight gain in the immediate post-operative period of 0–1.5 mo (F1,26Z 2.4, PZ0.1352), but a significant increase in weight from 1.5 to 6 mo after surgery, after stimulation was initiated (F1,26Z20.7, PZ0.0001). Six of the study patients gained in excess of 14 lb in the 6-mo post-operative period. Four of these patients were male and two female. The average age of these subjects was 60-yr-old. Examination of the average weight changes revealed that more subjects (nZ22) gained than lost weight (nZ5). Patients who lost weight had higher BMI on the day of surgery than those who gained weight (mean BMI of 30.4 vs. 25.7 kg/m2, respectively).
The average pre- and post-operative BMI changes (Table 1) in all patients and the subset for which 12 mo data were available paralleled weight changes. With all patients included, statistically significant BMI changes included an average BMI loss in the pre-operative period of 0.7 kg/m2 (F1,26Z6.4, PZ0.0178) and an average post-operative gain of 1.4 kg/m2 (F1,26Z20.1, PZ0.0001). There was no significant change in BMI during the first postoperative period (0–1.5 mo, F1,26Z2.2, PZ0.1503); all post-surgical gain occurred after the stimulator was activated. The average BMI on the day of surgery was 26.6 kg/m2. On the day of surgery, three subjects were underweight, nine were normal weight, eight were overweight, four were obese, and three were morbidly obese. In the subset for which 12 mo data were available, BMI was decreased by 0.9 kg/min2 in the pre-operative period (Table 1). This decrease is similar to that observed in the larger group, but significance was likely not reached because of limited power in the analysis resulting form low numbers.
Fig. 1. Six-mo pre- and post-surgical weights for all subjects (NZ27). Data shown are meanGstandard error. Data shown are meanGstandard error. *PZ0.0163 as compared to mean body weight in the K6 to 0 time period; ‡PZ0.0001 as compared to mean body weight on day of surgery.
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Fig. 2. Pre- and post-surgical weights for a subset of subjects in which data for the 12-mo pre- and post-STN DBS time-period was available (NZ10). Data shown are meanGstandard error. *PZ0.0002 as compared to mean body weight on day of surgery.
Like the larger group, there was no significant change in BMI in the 0–1.5 mo post-operative period (PZ0.9612, Table 1). In the 1.5–6 and 6–12 mo post-operative period, BMI was significantly increased by 1.4 kg/m2 (PZ0.0150, Table 1) and 1.8 kg/m2 (PZ0.0394), respectively, which resulted in a cumulative increase in BMI of 3.2 kg/m2 postoperatively in this group (PZ0.0001, Table 1).
5. Discussion Weight gain has been reported after functional neurosurgery for the treatment of PD. While on average the weight gain has been shown to be modest, previous research has been limited by small sample sizes and lack of preoperative data. This retrospective chart review was meant to replicate and extend the findings of previous studies. Our findings support previous research in documenting weight gain after DBS STN surgery. Our patients gained an average of 10.1 lbs in the first 6 mo after STN DBS (all included subjects) and an average of 20.3 lbs over 12 mo (smaller subset of included patients with 12 mo data available). Our 6-mo data are consistent with other reports in the literature [14,17,18] but our 12-mo data reveal much larger weight gain than has previously been reported. Importantly, in our patients, the slope of the mean weight gain appears to remain unchanged during the entire 12-mo post-operative
period, suggesting that weight gain likely continues beyond 1 yr after surgery. The present study also extends previous findings in evaluating not only weight but also BMI. The average BMI data in the pre-operative period (26.6 kg/m2) demonstrated that over 50% of our patients receiving STN DBS were overweight. The BMI values of the subjects in this study are surprising given the typical assumption that disease progression itself reduces weight and/or BMI in surgical PD patients. Indeed, an Italian study reported a preoperative mean BMI of 21.6 kg/m2 in their surgical subjects [14]. The discrepancy between our findings and those in the Italian study cannot be explained by cultural differences alone, since BMIs among healthy individuals are similar in the US and Italy. Three people in our study group were morbidly obese at the time of lead implantation. The fairly reliable finding that DBS results in weight gain in a majority of patients raises an important clinical question: should morbidly obese patients receive bariatric surgery prior to STN DBS, or should decisions about bariatric procedures be delayed until the extent of post-surgical weight gain can be appreciated? Furthermore, given that the exact mechanism of weight gain following STN DBS is unknown, is it prudent to even consider surgical weight loss intervention? The time course data presented in this study also raise the question of when, during the post-surgical period, decisions about weight
Table 1 BMI (kg/m2) changes Months pre-operative K12 to K6 All patients (NZ27) Subset (NZ10) *
No data 26.9G2.2
Surgery K6 to 0 27.3G1.4 26.4G2.2
Months post-operative
0
0–1.5 *
26.6G1.4 26.0G2.3
26.8G1.4 26.1G2.2
1.5–6
6–12 †
28.0G1.3 27.4G2.0†
P!0.02 as compared to mean body weight in the pre-surgery time period; †P!0.02 as compared to mean body weight on day of surgery.
No data 29.2G2.3†
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management strategies (with or without surgery) should be made. At present, there are no outcome data in PD patients with respect to bariatric surgery. Twenty-two percent of the study patients (nZ6) gained more than 14 pounds in the post-operative period. There were no obvious pre-operative characteristics that distinguished these patients from the other patients in our limited sample. Further research with more systematic attention to pre- and post-operative variables as they relate to weight gain is urgently needed so that patient risk can be assessed as part of the decision about whether to recommend DBS. As part of this assessment, it may be worthwhile to consider the possibility that for some patients, weight gain after DBS may be a homeostatic response to disease-related weight loss, unique to a given patient. Nevertheless, even a small weight gain may result in functional disability in a patient who is already de-conditioned from long-standing PD. In consideration of the findings of this study and previous research, it would be prudent to monitor the DBS population carefully with periodic weighing and BMI calculations to identify those patients gaining excessive weight in the postoperative period and to make treatment recommendations early. A comprehensive assessment of those in the overweight, obese and morbidly obese categories should be completed with particular attention to medical co-morbidities, medications, diet, exercise and activity levels [20–22]. Referral to a dietician may be appropriate for assessment and counseling. In morbidly obese and obese patients, it is recommended that the patient be referred to a center with experience in surgical and non-surgical approaches to weight management [21,23]. It is important to recognize, however, that weight loss strategies that may be appropriate for the general population (i.e. aerobic exercise) may not be appropriate in the DBS population because of the loss of function that may accompany PD. Similar attention must be given to those patients in an underweight BMI category to ensure adequate nutritional status before and after surgery. Dysphagia and difficulty with feeding due to motor difficulties may be potential causes of a low weight and BMI. A dietician may be able to recommend higher energy foods that can be tailored to the patient’s motor impairment or dysphagia status. In severe cases, total parenteral nutrition or feedings via percutaneous endoscopic gastrostomy (PEG) tubes are warranted [24,25]. Potential limitations of this study include the reliance on retrospective data and the lack of control for post-operative or pre-operative factors that could influence weight changes. Future research could be directed at prospectively identifying pre-operative patient characteristics predictive of weight gain after STN DBS. In addition, the use of bariatric weight loss surgery in this population needs further exploration. Finally, conclusive research to elucidate the mechanism of weight gain after STN DBS would significantly advance the development of directed treatment strategies to manage weight gains.
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Acknowledgements The authors would like to thank Shilpa Seshadri, MS and Lisa Brauer, PhD for their help and expertise in the preparation of this manuscript.
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