Thalamic DBS for Neuropathic Pain After Amputation
Table 1 lists the demographic characteristics of 12 consecutive patients treated over 3 years with DBS surgeries between January 2009 and May 2011, including pain origin, relevant preoperative medications, stimulation parameters, and baseline preoperative and long-term (12-month) postoperative VAS scores. Ten patients (83%) were male, 2 female (17%), and the mean age of the study population was 53.6 ± 9.8 years old. All patients suffered traumatic injuries, and only 1 was not due to a motor vehicle accident. All amputees experienced phantom pain and all BPAs had preganglionic involvement. No patients with BPA underwent amputations and no amputees had BPA. The mean duration of symptoms before surgery was 20 ± 13.4 years. One patient with BPA underwent an unsuccessful postoperative trial of externalized DBS due to lack of efficacy despite intraoperative paresthesia. Eleven patients proceeded to full DBS implantation after successful intraoperative and postoperative trials and completed postoperative follow-up duration of 1 year. There were no significant surgical complications in this series and side effects from stimulation were unremarkable. No patients have required electrode or implantable pulse generator revisions to date (as of June 2013). All patients received continuous bipolar DBS with patient control of amplitude up to a clinician-set maximum.
Table 1 and Table 2 also summarize baseline patient-reported outcome measures for those patients proceeding to full implantation of the DBS system. There were no statistically significant differences in baseline characteristics between pain etiologies. Figure 1 illustrates baseline scores and improvements across the entire 11-patient cohort for all outcome measures. At 1 month after surgery, mean VAS score improved by 60.1% ± 27.3% (p < 0.001), SF-36 improved by 30.1% ± 75.5% (p = 0.553), UWNPS improved by 47.1% ± 37.1% (p < 0.001), and BPI improved by 51.4% ± 33.3% (p < 0.001). Throughout the first year, mean pain relief was sustained, and at 12 months the VAS score was improved from before surgery by 69.6% ± 29.6% (p < 0.001), SF-36 improved by 34.6% ± 69.1% (p = 0.093), UWNPS improved by 50.8% ± 41.2% (p < 0.001), and BPI improved by 57.3% ± 37.8% (p < 0.001).
(Enlarge Image)
Figure 1.
Bar graphs showing overall outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), preoperatively and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. **p < 0.01 (highly statistically significant). Open circles indicate outliers.
Although both amputation and BPA subgroups showed significant improvements initially with DBS sustained for 1 year (Table 3, Figs. 2 and 3), amputation pain improved the most, with benefits sustained across all pain outcome measures. The BPA pain improvements in overall outcome scores were restricted to the VAS. In the amputation group, after 12 months the mean VAS score improved by 90.0% ± 10.0% (p < 0.001), SF-36 improved by 57.5% ± 97.9% (p = 0.127), UWNPS improved by 80.4% ± 12.7% (p < 0.001), and BPI improved by 79.9% ± 14.7% (p < 0.001). In the BPA group, after 12 months the mean VAS score improved by 52.7% ± 30.2% (p < 0.001), SF-36 improved by 15.6% ± 30.5% (p = 1.000), U WNPS improved by 26.2% ± 40.8% (p = 0.399), and BPI improved by 38.4% ± 41.7% (p = 0.018).
(Enlarge Image)
Figure 2.
Amputation subgroup outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), before surgery (preop) and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. *p < 0.05 (statistically significant), **p < 0.01 (highly statistically significant). Open circles indicate outliers.
(Enlarge Image)
Figure 3.
Brachial plexus avulsion subgroup outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), before surgery (pre-op) and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. *p < 0.05 (statistically significant), **p < 0.01 (highly statistically significant). Open circles indicate outliers.
Despite considerable improvements in pain scores, statistically significant overall improvements in SF-36 were not observed, with the exception of amputation pain 1 month after surgery, which improved by 71.4% ± 98.1% (p = 0.013). However, analyses of SF-36 subscores across the entire cohort demonstrated significant and sustained improvements in bodily pain (p < 0.001 throughout) and physical functioning (p = 0.08 at 6 months), with improvements in physical role and general health also approaching statistical significance. In contrast to anecdotal patient reports (Video 1), social functioning, vitality, and emotional and mental health were not significantly improved. Highly significant improvements (p < 0.001) were observed in most UWNPS subscores including sharp, hot, intense, dull, deep, and unpleasant pain, but not cold, sensitive, and itchy pain. Statistical analyses of these subscores by etiological subgroup was not performed to avoid Type I errors, although considerable reductions in hot, sharp, deep, and dull UWNPS subscores in both amputation and BPA pain subgroups suggest DBS relieved both the continuous and paroxysmal components of neuropathic pain. The BPI improvements were statistically significant (p < 0.001) in both severity and interference domains.
Results
Table 1 lists the demographic characteristics of 12 consecutive patients treated over 3 years with DBS surgeries between January 2009 and May 2011, including pain origin, relevant preoperative medications, stimulation parameters, and baseline preoperative and long-term (12-month) postoperative VAS scores. Ten patients (83%) were male, 2 female (17%), and the mean age of the study population was 53.6 ± 9.8 years old. All patients suffered traumatic injuries, and only 1 was not due to a motor vehicle accident. All amputees experienced phantom pain and all BPAs had preganglionic involvement. No patients with BPA underwent amputations and no amputees had BPA. The mean duration of symptoms before surgery was 20 ± 13.4 years. One patient with BPA underwent an unsuccessful postoperative trial of externalized DBS due to lack of efficacy despite intraoperative paresthesia. Eleven patients proceeded to full DBS implantation after successful intraoperative and postoperative trials and completed postoperative follow-up duration of 1 year. There were no significant surgical complications in this series and side effects from stimulation were unremarkable. No patients have required electrode or implantable pulse generator revisions to date (as of June 2013). All patients received continuous bipolar DBS with patient control of amplitude up to a clinician-set maximum.
Table 1 and Table 2 also summarize baseline patient-reported outcome measures for those patients proceeding to full implantation of the DBS system. There were no statistically significant differences in baseline characteristics between pain etiologies. Figure 1 illustrates baseline scores and improvements across the entire 11-patient cohort for all outcome measures. At 1 month after surgery, mean VAS score improved by 60.1% ± 27.3% (p < 0.001), SF-36 improved by 30.1% ± 75.5% (p = 0.553), UWNPS improved by 47.1% ± 37.1% (p < 0.001), and BPI improved by 51.4% ± 33.3% (p < 0.001). Throughout the first year, mean pain relief was sustained, and at 12 months the VAS score was improved from before surgery by 69.6% ± 29.6% (p < 0.001), SF-36 improved by 34.6% ± 69.1% (p = 0.093), UWNPS improved by 50.8% ± 41.2% (p < 0.001), and BPI improved by 57.3% ± 37.8% (p < 0.001).
(Enlarge Image)
Figure 1.
Bar graphs showing overall outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), preoperatively and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. **p < 0.01 (highly statistically significant). Open circles indicate outliers.
Although both amputation and BPA subgroups showed significant improvements initially with DBS sustained for 1 year (Table 3, Figs. 2 and 3), amputation pain improved the most, with benefits sustained across all pain outcome measures. The BPA pain improvements in overall outcome scores were restricted to the VAS. In the amputation group, after 12 months the mean VAS score improved by 90.0% ± 10.0% (p < 0.001), SF-36 improved by 57.5% ± 97.9% (p = 0.127), UWNPS improved by 80.4% ± 12.7% (p < 0.001), and BPI improved by 79.9% ± 14.7% (p < 0.001). In the BPA group, after 12 months the mean VAS score improved by 52.7% ± 30.2% (p < 0.001), SF-36 improved by 15.6% ± 30.5% (p = 1.000), U WNPS improved by 26.2% ± 40.8% (p = 0.399), and BPI improved by 38.4% ± 41.7% (p = 0.018).
(Enlarge Image)
Figure 2.
Amputation subgroup outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), before surgery (preop) and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. *p < 0.05 (statistically significant), **p < 0.01 (highly statistically significant). Open circles indicate outliers.
(Enlarge Image)
Figure 3.
Brachial plexus avulsion subgroup outcomes according to the VAS (A), SF-36 (B), UWNPS (C), and BPI (D), before surgery (pre-op) and at 1, 3, 6, and 12 months after surgery. The median is indicated by the horizontal line inside the boxes, which represent 2 quartiles, and the whiskers show minimum and maximum values. Asterisks indicate the statistical significance of the difference between the postsurgery and presurgery scores. *p < 0.05 (statistically significant), **p < 0.01 (highly statistically significant). Open circles indicate outliers.
Despite considerable improvements in pain scores, statistically significant overall improvements in SF-36 were not observed, with the exception of amputation pain 1 month after surgery, which improved by 71.4% ± 98.1% (p = 0.013). However, analyses of SF-36 subscores across the entire cohort demonstrated significant and sustained improvements in bodily pain (p < 0.001 throughout) and physical functioning (p = 0.08 at 6 months), with improvements in physical role and general health also approaching statistical significance. In contrast to anecdotal patient reports (Video 1), social functioning, vitality, and emotional and mental health were not significantly improved. Highly significant improvements (p < 0.001) were observed in most UWNPS subscores including sharp, hot, intense, dull, deep, and unpleasant pain, but not cold, sensitive, and itchy pain. Statistical analyses of these subscores by etiological subgroup was not performed to avoid Type I errors, although considerable reductions in hot, sharp, deep, and dull UWNPS subscores in both amputation and BPA pain subgroups suggest DBS relieved both the continuous and paroxysmal components of neuropathic pain. The BPI improvements were statistically significant (p < 0.001) in both severity and interference domains.
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