We reviewed 209 patient records. Nine patients missed follow-up appointments or had inadequate medical records for the 6 months following the procedure. Twenty-five patients underwent other interventional procedures within the 6 months of continuous epidural infusion. In one patient, the catheter could not be maintained for more than 10 days due to side effects associated with the continuous epidural infusion. Two patients did not receive antiviral drugs at the beginning of the herpes zoster episode. During the 6-month follow-up period, two patients reported other painful diseases. The medical records of those patients were excluded from the final analysis. Additionally, eight patients stopped using anticonvulsants and analgesics due to drug-associated side effects after the procedure, and 48 patients received other drugs, such as opioids, via the epidural catheter. To prevent drug-induced bias, these patients were also excluded from the final analysis. Finally, the medical records of 114 patients were analyzed and 57 patients each were assigned to the contrast and stimulation groups (Figure 3).
There were no significant differences in baseline demographics between the groups (Table 1). Bonferroni post-hoc tests revealed that the pain scores at each time point after the procedure were significantly lower than those at baseline in both groups (Table 2).
Table 1. Baseline characteristics of the patients
|
Acute HZ
(≤ 30 days)
Contrast group
(n = 57)
|
Acute HZ
(≤ 30 days)
Stimulation group
(n = 57)
|
P value
|
Age (years)
|
67.0 ± 10.3
|
66.2 ± 11.7
|
P = 0.72
|
Sex (M/F)
|
25/32
|
16/41
|
P = 0.12
|
Site of HZ infection
|
C: 14
T: 36
L: 7
|
C: 13
T: 33
L: 11
|
P = 0.52
|
HTN
|
26 [46% (33, 58%)]
|
21 [37% (26, 50%)]
|
P = 0.45
|
DM
|
11 [19% (11, 31%)]
|
16 [28% (18, 41%)]
|
P = 0.38
|
Asthma
|
3 [5% (2, 14%)]
|
1 [2% (0, 9%)]
|
P = 0.62
|
Hepatic disease
|
5 [9% (4, 19%)]
|
3 [5% (2, 14%)]
|
P = 0.72
|
Kidney disease
|
2 [4% (1, 12%)]
|
3 [5% (2, 14%)]
|
P = 1.0
|
Avg. amount of ropivacaine in infusion device (ml)
|
37.7 ± 3.8
|
37.5 ± 4.0
|
P = 0.79
|
Baseline pain score*
|
8 [7–8]
|
8 [7–8]
|
P = 0.22
|
HZ: herpes zoster, HTN: hypertension, DM: diabetes mellitus, Avg: average, * Pain score on an 11-point (0–10) numerical rating scale, C: cervical, T: thoracic, L: lumbar.
Data are represented as mean ± standard deviation, median [interquartile range], or number [% (95% confidence interval)].
Table 2. Comparison with baseline pain score at each time point
Group
|
Contrast group
|
Stimulation group
|
Period A
|
Period B
|
Average difference (a−b)
|
P value
|
Average difference (a−b)
|
P value
|
Baseline pain score*
|
(1)
|
3.97
|
P < 0.001
|
4.25
|
P < 0.001
|
(2)
|
4.62
|
P < 0.001
|
5.51
|
P < 0.001
|
(3)
|
4.47
|
P < 0.001
|
5.21
|
P < 0.001
|
(4)
|
4.88
|
P < 0.001
|
5.65
|
P < 0.001
|
(5)
|
5.25
|
P < 0.001
|
5.88
|
P < 0.001
|
* Pain score on an 11-point (0–10) numerical rating scale. (1) Pain score immediately after epidural procedure, (2) Pain score 14 days after epidural procedure, (3) Pain score 1 month after epidural procedure, (4) Pain score 3 months after epidural procedure, (5) Pain score 6 months after epidural procedure. Data were analyzed using the Bonferroni post-hoc test. P value < 0.01 was considered statistically significant.
When the post-procedure pain scores of the two groups were compared, (after correcting for confounding variables), no significant differences were observed immediately after the procedure; however, there were significant differences in the post-procedure pain scores between the two groups after the 14th day, and up to the sixth month (Table 3).
Table 3. Comparison of pain scores between groups after correction for confounding variables
|
Acute HZ
(≤ 30 days)
Contrast group
(n = 57)
|
Acute HZ
(≤ 30 days)
Stimulation group
(n = 57)
|
P value
|
Baseline pain score
|
7.4 ± 1.5
|
7.2 ± 1.5
|
P = 0.28
|
Pain score* immediately after epidural procedure
|
3.5 ± 2.0
|
2.9 ± 1.8
|
P = 0.25
|
Pain score* 14 days after epidural procedure
|
2.8 ± 1.9
|
1.7 ± 0.8
|
P = 0.001
|
Pain score* 1 month after epidural procedure
|
3.0 ± 2.1
|
1.9 ± 1.1
|
P = 0.01
|
Pain score* 3 months after epidural procedure
|
2.6 ± 1.8
|
1.5 ± 1.2
|
P = 0.001
|
Pain score* 6 months after epidural procedure
|
2.2 ± 1.8
|
1.3 ± 1.1
|
P = 0.01
|
HZ: herpes zoster, * Pain score on an 11-point (0–10) numerical rating scale.
Data are represented as adjusted mean ± standard deviation. Data were analyzed for the difference in pain scores between the groups using covariance analysis. Adjustments were made for age, sex, timing from rash to epidural procedure, location of herpes zoster, hypertension, diabetes mellitus, asthma, hepatic disease, and kidney disease.
The difference between the post-procedure pain scores of the two groups was analyzed at each level. The cervical and thoracic level results were similar to those of the entire analysis. However, there was no significant difference between the two groups in the lumbar area, which was an affected site for a small number of patients (Table 4).
Table 4. Comparison of pain scores between the groups for cervical, thoracic, and lumbar levels
|
Cervical area
|
Thoracic area
|
Lumbar area
|
|
Acute HZ
(≤ 30 days)
Contrast group
(n = 14)
|
Acute HZ
(≤ 30 days)
Stimulation group
(n = 13)
|
P value
|
Acute HZ
(≤ 30 days)
Contrast group
(n = 36)
|
Acute HZ
(≤ 30 days)
Stimulation group
(n = 33)
|
P value
|
Acute HZ
(≤ 30 days)
Contrast group
(n = 7)
|
Acute HZ
(≤ 30 days)
Stimulation group
(n = 11)
|
P value
|
Baseline pain score
|
7.8 ± 1.4
|
6.9 ± 1.3
|
P = 0.13
|
7.4 ± 1.6
|
7.2 ± 1.5
|
P = 0.85
|
7.1 ± 1.7
|
7.3 ± 2.0
|
P = 0.9
|
Pain score* immediately after epidural procedure
|
3.8 ± 2.0
|
3.0 ± 2.1
|
P = 0.44
|
3.5 ± 2.0
|
3.1 ± 1.7
|
P = 0.51
|
3.0 ± 1.8
|
2.1 ± 1.8
|
P = 0.58
|
Pain score* 14 days after epidural procedure
|
3.2 ± 2.1
|
1.7 ± 0.8
|
P = 0.02
|
2.8 ± 1.9
|
1.7 ± 0.9
|
P = 0.03
|
2.3 ± 1.0
|
1.5 ± 0.8
|
P = 0.08
|
Pain score* 1 month after epidural procedure
|
3.4 ± 2.5
|
1.9 ± 1.2
|
P = 0.06
|
2.9 ± 2.1
|
2.0 ± 1.1
|
P = 0.19
|
2.7 ± 1.5
|
1.6 ± 1.1
|
P = 0.12
|
Pain score* 3 months after epidural procedure
|
2.3 ± 1.3
|
1.3 ± 1.3
|
P = 0.04
|
2.6 ± 2.0
|
1.6 ± 1.1
|
P = 0.04
|
2.9 ± 2.0
|
1.3 ± 1.2
|
P = 0.07
|
Pain score* six months after epidural procedure
|
2.2 ± 1.8
|
1.2 ± 1.1
|
P = 0.03
|
2.2 ± 1.8
|
1.3 ± 1.1
|
P = 0.08
|
2.3 ± 1.6
|
1.2 ± 1.2
|
P = 0.46
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
HZ: herpes zoster, * Pain score on an 11-point (0–10) numerical rating scale.
Data are represented as adjusted mean ± standard deviation. Data were analyzed for differences in pain score between the groups using covariance analysis. Adjustments were made for age, sex, timing from rash to epidural procedure, hypertension, diabetes mellitus, asthma, hepatic disease, and kidney disease.
The proportion of patients with complete remission was 1.90 times higher in the stimulation group than in the contrast group (Table 5).
Table 5. Comparison of complete remission between contrast and stimulation groups during the 6-month follow-up period after each procedure
|
Contrast
Group
|
Stimulation
Group
|
Adjusted OR
(95% CI)
Reference: contrast group
|
P value
|
Acute HZ
(≤3 0 days)
|
29/57
[51% (38, 63%)]
|
41/57
[72% (59, 82%)]
|
1.90 (0.81–4.44)
|
P = 0.14
|
HZ: herpes zoster, OR: odds ratio, CI: confidence interval.
Complete remission is defined as a pain score of less than 2 with no further medication. Data are represented as number [% (95% confidence interval)] and were analyzed by logistic regression analysis. Adjustments were made for age, sex, location of herpes zoster, days from the onset of rash to procedure, hypertension history, diabetes mellitus history, asthma history, hepatic disease history, kidney disease history, and baseline pain score.
The proportion of patients who underwent other interventional procedures within 6 months after continuous epidural infusion due to insufficient pain control was 3.62 times higher in the contrast group than in the stimulation group (Table 6).
Table 6. Comparison of implemented procedures due to insufficient pain control during the 6-month follow-up period
|
Contrast
Group
|
Stimulation
Group
|
Adjusted OR
(95% CI)
Reference: stimulation group
|
P value
|
Acute HZ
(≤30 days)
|
20/77
[26% (17, 37%)]
|
5/62
[8% (3, 18%)]
|
3.62 (1.17-11.19)
|
P = 0.03
|
HZ: herpes zoster, OR: odds ratio, CI: confidence interval
Data are represented as number [% (95% confidence interval)]. Data were analyzed by logistic regression analysis. Adjustments were made for age, sex, location of herpes zoster, days from the onset of rash to procedure, hypertension history, diabetes mellitus history, asthma history, hepatic disease history, kidney disease history, and baseline pain score.