Comparative long-term efficacy of short-term spinal cord stimulation versus bipolar pulsed radiofrequency for refractory postherpetic neuralgia: a 24 month prospective study

Abstract

Background

Postherpetic neuralgia (PHN) is a debilitating neuropathic pain condition that persists after herpes zoster infection, often resistant to conventional medications. This study compares the long-term efficacy and safety of short-term spinal cord stimulation (stSCS) versus bipolar pulsed radiofrequency (bPRF) in managing refractory PHN.

Methods

In this prospective, controlled observational study, 140 PHN patients (aged ≥ 18 years; PHN duration ≥ 3 months) with inadequate pain relief from standard therapies were enrolled and randomized equally into two groups (n = 70 each). The stSCS group received percutaneous implantation of an 8-contact electrode for temporary neuromodulation, while the bPRF group underwent application of controlled high-frequency pulses to the dorsal root ganglion. Outcome measures included pain intensity (VAS, NRS), neuropathic pain characteristics (DN4), quality of life (SF-36, EQ-5D), sleep quality (PSQI), and psychological status (SAS, SDS), assessed at baseline and at follow-up intervals over 24 months.

Results

Both stSCS and bPRF achieved significant short-term pain relief. However, from 6 to 24 months post-treatment, the stSCS group demonstrated significantly lower VAS scores and superior pain control compared to the bPRF group. In addition, improvements in sleep quality and emotional well-being were more pronounced in the stSCS group at 12, 18, and 24 months. Both treatments exhibited favorable safety profiles with only minor, transient adverse events reported.

Conclusions

While both stSCS and bPRF effectively alleviate pain in patients with refractory PHN, stSCS offers superior long-term benefits in pain reduction, sleep quality, and psychological outcomes. These findings suggest that stSCS may be the preferred neuromodulation strategy for patients with chronic PHN requiring sustained symptom management.

Introduction

Postherpetic neuralgia (PHN) represents a significant and disabling neuropathic pain condition persisting after herpes zoster infection, with prevalence rates of 10–20% among individuals affected by shingles [1, 2]. The pathophysiology of PHN encompasses a multifaceted interplay of peripheral nerve damage, inflammation of the dorsal root ganglion, and central sensitization mechanisms, manifesting clinically as allodynia, dysesthesia, and persistent burning pain [3, 4]. Conventional pharmacological approaches including anticonvulsants, tricyclic antidepressants, opioid analgesics, and topical agents frequently provide inadequate pain control or produce intolerable adverse effects, necessitating exploration of alternative therapeutic modalities [5, 6].

In response to the limitations of conventional treatments, interventional neuromodulation techniques have gained attention as promising alternatives for refractory PHN [7]. Spinal cord stimulation (SCS) has demonstrated efficacy in pain management but typically requires permanent implantation, which can be associated with high costs, surgical risks, and long-term maintenance challenges. To address these concerns, short-term SCS (stSCS) has been developed as a less invasive alternative. Emerging evidence suggests that stSCS provides comparable pain relief and functional improvement while avoiding the long-term commitment of permanent implantation [8]. Concurrently, bipolar pulsed radiofrequency (bPRF) offers a distinct neuromodulatory mechanism by delivering controlled high-frequency electrical pulses that modify neural signaling patterns without inducing structural nerve damage [9, 10]. Despite initial encouraging outcomes with both modalities, there exists a paucity of longitudinal comparative evidence examining their sustained efficacy, functional outcomes, and safety profiles in PHN management. This research gap is particularly significant given the chronic nature of PHN and the substantial impact of persistent pain on patients'quality of life and psychological wellbeing [11].

The present investigation aims to conduct a rigorous comparison of stSCS and bPRF in the management of refractory PHN through a 24-month prospective evaluation. We hypothesize that while both interventions will demonstrate pain-alleviating properties, stSCS will exhibit superior long-term outcomes across multiple dimensions, including sustained analgesic effect, quality of life parameters, sleep architecture, and psychological functioning. This comprehensive assessment will provide essential clinical guidance for optimal neuromodulation selection in this challenging patient population.

Materials and methods

Study design

This prospective, controlled observational study was conducted at a tertiary medical center to evaluate the long-term clinical efficacy and safety of stSCS versus bPRF in patients with refractory PHN. A total of 140 patients were enrolled between January 2021 and December 2022. Patients meeting the inclusion criteria were randomized using a computer-generated sequence into two groups (n = 70 per group). Randomization was performed using a computer-generated sequence, with allocation concealment managed by an independent statistician. Outcome assessors were blinded to treatment allocation, while blinding of patients and interventionalists was not feasible due to the nature of the procedures. Written informed consent was obtained from all participants, and the study was approved by the Institutional Review Board of Shandong Provincial Hospital (No.2021-slyy-018). The study protocol was prospectively registered at the Chinese Clinical Trial Registry (No. ChiCTR2000039059) and conducted in accordance with the principles of the Declaration of Helsinki and Good Clinical Practice guidelines.

Participants

Patients were eligible for inclusion if they were aged 18 years or older, with a confirmed diagnosis of PHN for at least 3 months, and had inadequate pain relief from conventional treatments such as anticonvulsants, tricyclic antidepressants, opioids, or topical analgesics. Patients were excluded if they had a history of spinal surgery or preexisting neurological disorders that could affect pain perception, an active systemic infection or coagulopathy that contraindicated interventional procedures, or a psychiatric disorder severe enough to interfere with study participation. Individuals with significant cardiopulmonary comorbidities that might increase the procedural risk were also excluded. A detailed CONSORT-style flow diagram of patient screening, enrollment, allocation, and follow-up is provided in Fig. 1.

Fig. 1

CONSORT flow diagram of patient enrollment and follow-up. This figure illustrates the study flow from initial screening to patient allocation and follow-up. A total of 140 patients were enrolled and equally distributed between the stSCS and bPRF groups. The diagram details the number of patients assessed for eligibility, exclusions (with reasons), allocation to treatment arms, and follow-up at designated intervals (1, 3, 6, 12, 18, and 24 months)

Surgical interventions

All procedures were performed by associate chief physicians or senior specialists with extensive experience in interventional pain management.

Spinal cord stimulation (stSCS)

stSCS was conducted under local anesthesia with continuous electrocardiogram (ECG) monitoring. Patients were positioned prone on the operating table, and the spinal cord segment to be stimulated was determined based on dermatomal mapping of the pain distribution. After sterile preparation of the surgical field, an 8-contact electrode (977D260, Medtron) was introduced percutaneously via a puncture needle and positioned over the dorsal aspect of the target spinal cord segment under fluoroscopic guidance. The fluoroscopic views during electrode placement are shown in Fig. 2A and B, where the anteroposterior view (Fig. 2A) demonstrates the implantation of spinal cord stimulation electrodes, and the lateral view (Fig. 2B) shows the electrode trajectory along the spinal column. Intraoperative stimulation testing was performed to confirm adequate coverage of the painful region, and stimulation parameters were adjusted accordingly. If pain coverage was satisfactory and no complications such as bleeding or discomfort were observed, the electrode was secured, and the patient was returned to the ward. Postoperative stimulation parameters were set with a frequency of 40–100 Hz, a pulse width of 40–200 μs, and a self-controlled amplitude voltage of 1–10 V.

Fig. 2

Fluoroscopic views of electrode placement for stSCS and bPRF. A Anteroposterior fluoroscopic view demonstrating the implantation of spinal cord stimulation electrodes; B lateral fluoroscopic view showing the electrode trajectory along the spinal column; C anteroposterior view illustrating the placement of bipolar pulsed radiofrequency needles at the target site; D lateral view confirming the accurate positioning of bipolar pulsed radiofrequency needles relative to vertebral structures

Bipolar pulsed radiofrequency

Bipolar pulsed radiofrequency treatment was also performed under local anesthesia with continuous ECG monitoring. The target spinal nerve root segments were identified based on the patient’s most severe pain site and the distribution of cutaneous lesions, with two nerve root levels treated per session. Under fluoroscopic or ultrasound guidance, a percutaneous puncture was performed to access the intervertebral foramen of the affected spinal nerve root. Once the target site was reached, a radiofrequency electrode (R-2000B D1, BNS) was introduced and connected to the radiofrequency generator. Sensory and motor testing was conducted to ensure precise needle placement, with sensory stimulation at 50 Hz and 0.4 V used to elicit abnormal sensations at the pain site and motor stimulation at 2 Hz and 0.8 V used to confirm appropriate localization via induction of muscle contractions. The fluoroscopic views during bPRF needle placement are shown in Fig. 2C and D, where the anteroposterior view (Fig. 2C) illustrates the placement of bipolar pulsed radiofrequency needles at the target site, and the lateral view (Fig. 2D) confirms the accurate positioning of bipolar pulsed radiofrequency needles relative to vertebral structures. The bipolar pulsed radiofrequency mode was activated with an initial treatment voltage of 70 V, which was gradually increased to a maximum of 100 V depending on patient tolerance. Treatment was delivered at a pulse frequency of 2 Hz, a pulse width of 20 μs, and a target temperature of 45 °C for a total duration of 900 s per segment. Upon completion of the procedure, an anti-inflammatory and analgesic solution comprising 5 mL of 2% lidocaine, 10 mL of normal saline, and 5 mg (1 mL) of betamethasone was prepared. Following the modulation of each dorsal root ganglion, 3 mL of this solution was administered via the puncture needle at the treated segment. The patient was then monitored for 10 min postoperatively, and in the absence of any adverse reactions, was safely transferred back to the ward.

Outcome measures

The primary outcome of the study was the reduction in pain intensity, as assessed by changes in the VAS and Numeric Rating Scale (NRS, 0–10) at each follow-up time point. Secondary outcomes included assessments of neuropathic pain characteristics using the DN4 questionnaire, quality of life changes through the SF-36 and EQ-5D instruments, and improvements in sleep quality based on the Pittsburgh Sleep Quality Index (PSQI). Safety outcomes included the incidence of procedural complications, such as infection, device migration (in the stSCS group), and nerve irritation (in the bPRF group), as well as the need for retreatment or additional interventions. Clinical evaluations were performed at baseline and at follow-up intervals of 1, 3, 6, 12, 18, and 24 months after treatment. To minimize bias, investigators who performed the clinical evaluations, including pain intensity assessments and quality of life measurements, were blinded to the treatment allocation of the patients throughout the study period.

Statistical analysis

All analyses were conducted using SPSS version 27.0 (IBM Corp.). Continuous variables are reported as means ± standard deviations, and categorical variables as frequencies (%). Group comparisons were performed using Student’s t-test or ANOVA for continuous variables and Chi-square tests for categorical variables. For longitudinal outcomes, repeated-measures ANOVA was employed. Normality and sphericity assumptions were verified via Shapiro–Wilk and Mauchly’s tests, respectively, with Greenhouse–Geisser correction applied when sphericity was violated. To mitigate the risk of type I error from multiple comparisons, Bonferroni correction was used for post hoc analyses. A two-sided p-value < 0.05 was considered statistically significant.

Results

Patient characteristics

A total of 140 patients diagnosed with PHN were enrolled in the study, with 70 patients assigned to the stSCS group and 70 patients to the bPRF group. The mean age of patients was 67.2 ± 9.7 years in the stSCS group and 68.1 ± 8.9 years in the bPRF group, with no statistically significant difference between the two groups (p = 0.058). There were no significant differences in gender distribution, PHN duration, or affected dermatome segments between the groups (p > 0.05 for all variables), ensuring comparability at baseline. See Table 1 for details.

Table 1 Baseline characteristics of the study population

Pain relief outcomes

Both treatment modalities yielded a statistically significant reduction in pain intensity as measured by the VAS. Short-term outcomes (1–3 months) were comparable between the two groups; however, the stSCS group maintained significantly lower VAS scores from 6 to 24 months compared with the bPRF group (p < 0.05). At the 24 month follow-up, the mean VAS score was 2.6 ± 0.7 in the stSCS group versus 4.2 ± 1.1 in the bPRF group. These longitudinal changes in pain intensity are graphically represented in Fig. 3.

Fig. 3

Longitudinal changes in pain scores (VAS) over 24 months. This figure displays the mean VAS scores for both the stSCS and bPRF groups at baseline and subsequent follow-up intervals (1, 3, 6, 12, 18, and 24 months). Error bars represent standard deviations. The graph highlights that, while both groups showed significant short-term pain relief, the stSCS group maintained superior pain control over the long term (p < 0.05 from 6 months onward). Asterisks denote statistically significant differences between groups at the corresponding time points

Quality of life and sleep improvement

Both groups experienced significant improvement in sleep quality (assessed via the PSQI) and mental health (assessed via the SAS and SDS). However, at 12, 18, and 24 months, stSCS demonstrated significantly greater improvements in sleep and emotional well-being compared to bPRF. These findings indicate that stSCS not only provided better long-term pain relief but also improved sleep and mental health more effectively than bPRF. The comprehensive improvements in sleep and mental health outcomes at the 24 month follow-up are further detailed in Fig. 4.

Fig. 4

Sleep and mental health outcomes at 24 months. This figure summarizes the improvements in sleep quality and mental health parameters at the 24 month follow-up. Bar graphs represent the PSQI, SAS, and SDS scores for both treatment groups. The stSCS group demonstrated significantly greater improvements compared to the bPRF group, with *p < 0.05 indicating statistically significant differences between the groups

Adverse events and safety profile

Both treatments were well tolerated, with no serious complications such as infection, permanent nerve damage, or device-related failure. However, minor complications were observed in both groups (see Table 2 for details). The overall complication rate was low, with no significant differences between the two groups (p > 0.05 for all events). These events were likely related to procedural stress or local anesthesia and resolved spontaneously within one week.

Table 2 Adverse events

Discussion

The findings of this study confirm that both stSCS and bPRF are effective in the treatment of PHN, with significant improvements in pain relief, sleep quality, and emotional well-being observed in both groups. These results are consistent with previous studies showing that both stSCS and PRF can provide substantial pain relief in PHN patients [9, 14, 15]. However, our study also reveals that while the short-term efficacy of both treatments is comparable, stSCS demonstrated superior long-term efficacy in controlling pain, improving quality of life, and enhancing sleep and mental health outcomes at 12-, 18-, and 24-months post-treatment.

Our study highlights the durability of pain relief associated with stSCS, with the VAS scores remaining significantly lower in the stSCS group compared to the bPRF group over the long-term follow-up period. These findings are in line with studies by Wan et al. (2021) and Xue et al. (2022), who reported that SCS is more effective in providing long-term pain control compared to other neuromodulatory treatments like PRF [9, 16]. The underlying mechanism of stSCS involves the modulation of pain signals at the spinal cord level, where electrical pulses inhibit the transmission of nociceptive signals. This action may contribute to the long-term efficacy of stSCS in maintaining pain relief even months after the intervention [12, 17].

In contrast, bPRF, while effective in providing pain relief, may not produce the same sustained benefits as stSCS. bPRF works by applying high-frequency pulses to the dorsal root ganglion, altering neuronal signaling without causing permanent nerve damage [18]. However, its pain-relieving effects tend to diminish over time, especially in chronic pain conditions like PHN. This may explain the shorter duration of effectiveness observed in the bPRF group in our study, as seen in the VAS score comparisons at 6, 12, 18, and 24 months post-treatment [19].

Both stSCS and bPRF led to significant improvements in sleep quality and reductions in anxiety and depression (as measured by the PSQI, SAS, and SDS scales). However, the stSCS group exhibited greater improvements in sleep and mental health at long-term follow-up (12, 18, and 24 months). These findings align with prior research that suggests neuromodulation therapies, particularly SCS, can ameliorate pain-related sleep disturbances and reduce the emotional burden associated with chronic pain [20, 21]. The better long-term outcomes in the stSCS group may be due to the continuous nature of spinal cord stimulation, which provides ongoing modulation of pain pathways over an extended period. In contrast, bPRF provides acute pain relief that may not extend to the emotional and sleep-related benefits seen with more continuous stimulation methods [22, 23]. This has important clinical implications for patients with chronic, persistent pain, suggesting that stSCS may offer a more comprehensive treatment option for PHN patients who suffer from both pain and the emotional impacts of the condition.

Both stSCS and bPRF were found to be safe, with only minor complications observed in a small proportion of patients [15, 24]. The overall complication rate was low, and all events resolved spontaneously within one week without requiring additional interventions. Transient headache and dizziness in the stSCS group may be attributed to the percutaneous electrode placement, while cerebrospinal fluid leaks are likely due to puncture site complications [25]. In the bPRF group, nausea and vomiting may be related to the local anesthesia or procedural stress. These findings are consistent with prior studies demonstrating the favorable safety profiles of stSCS and bPRF [26,27,28]. The transient nature of these adverse events underscores the minimally invasive nature of both treatments, making them suitable for elderly patients or those with comorbidities who require low-risk interventions. Furthermore, the excellent tolerability of both therapies supports their use in chronic pain management, where long-term adherence to treatment is critical [29].

The results of this study suggest that both stSCS and bPRF are effective and safe interventions for PHN. However, based on the long-term efficacy, stSCS may be the preferred option for patients with chronic PHN who require sustained pain relief and have associated sleep disturbances or mood disorders. The superior long-term results observed with stSCS make it an attractive option for elderly patients or those with refractory PHN who seek a durable solution to their chronic pain [30, 31]. Moreover, bPRF remains a viable alternative, particularly for patients who prefer a less invasive approach or those who are not candidates for implantation of an SCS device [9, 32]. bPRF may offer quicker recovery times and requires less long-term commitment from patients, making it an appealing choice for those with more acute or subacute pain [33].

Limitations and future research

Several limitations should be acknowledged in this study. First, the observational design without randomization may introduce selection bias, and a randomized controlled trial would provide stronger evidence of the comparative efficacy of stSCS and bPRF. Second, as this research was conducted at a single center, the findings may not be fully generalizable to a broader patient population. Future studies involving multiple centers and larger sample sizes would help validate these results. Finally, although our focus was on clinical outcomes, we did not deeply explore the neurophysiological mechanisms underlying the responses to stSCS and bPRF [4, 34]. Future investigations into these mechanisms and the potential benefits of combining these modalities could lead to even more effective treatment strategies.

Conclusions

This 24 month comparative study demonstrates that both stSCS and bPRF provide significant improvements in pain and quality of life for refractory PHN patients. However, stSCS offers superior long-term pain relief and greater improvements in sleep quality and emotional well-being, particularly evident from 6 months onward. These findings suggest that stSCS should be considered as a preferred neuromodulation approach for patients with chronic, refractory PHN, especially when long-term symptom control is the therapeutic goal. Future research should explore novel SCS paradigms and optimal patient selection criteria to maximize treatment benefits while minimizing invasiveness.