Medical records were obtained from all patients who received pulsed radiofrequency therapy for herpes-related pain (AHN or PHN) from January 2020 to September 2022. We included the medical records of 243 patients with herpes zoster-related pain (AHN or PHN) in a thoracic segment (Figure 1). A total of 281 patients were included before follow-up, of which 38 were lost to follow-up (three deceased and 35 lost contact). Data such as sex, age, height, weight, BMI, preoperative VAS, smoking status, drinking status, hypertension, diabetes, insomnia, and postoperative oral medication of patients were recorded.

Pain intensity (measured using the Visual Analog Scale, VAS), sleep quality (measured using the Athens Insomnia Scale, AIS), and psychological burden (measured using the Generalized Anxiety Disorder-7 items, GAD-7, and the Patient Health Questionnaire-9 items, PHQ-9) of patients were followed up at 1 week, 1 month, 3 months, 6 months, and 12 months after the operation. The therapeutic effects between the two groups were compared.

The study was approved by the Ethics Committee of the First Affiliated Hospital of Xi'an Jiaotong University (KYLLSL-2022-205).

Patients were included if they met the following inclusion criteria: (1) Met the diagnostic criteria of HZ and PHN; (2) the lesion occurred in the thoracic spinal nerves; (3) persistent intense pain, with/without local skin hyperalgesia, sensory abnormalities; (4) pain levels not well controlled by standard pharmacotherapy (antiepileptic drugs, antidepressants, lidocaine patches, opioids, etc.); and (5) 24-h VAS ≥5. After the preliminary selection, patients were excluded if they had the following exclusion criteria: (1) unwillingness or inability to complete the follow-up; (2) severe coagulation disorder; (3) severe liver or kidney dysfunction; (4) history of drug abuse; (5) severe cardiopulmonary disease; or (6) intellectual inability to complete self-evaluation using VAS or AIS.

The application of PRF to the DRG in treating all patients with either AHN or PHN in the thoracic segment was performed by the same team of doctors. Continuous ECG monitoring was carried out throughout the procedure, and the diseased spinal nerve was preoperatively determined, based on the patient's pain site. The patient was in the prone position for the surgical procedure. The surgical area was disinfected routinely. Under local infiltration anesthesia, a needle with a 5 mm exposed tip was inserted layer by layer into the DRG of the spinal nerve under C-arm guidance (Figure 2). Upon reaching the expected position, a high-frequency (50 Hz, 500 μs width, < 0.2 volts) sensory stimulation test and a low-frequency (2 Hz, 1,000 μs width, < 0.5 volts) motor stimulation test were conducted. These tests confirmed the accurate placement of the needle tip. Subsequently, the treatment was carried out with PRF parameters set at 42°C, 2 Hz, with a field intensity of 90 V, for a duration of 900 s.

During follow-up, it was found that some patients continued to take oral medications, such as pregabalin and opioids, due to poor response to PRF. These cases were recorded and analyzed. However, due to the extended follow-up period, accurate information on the oral doses and treatment courses of the drugs for many patients could not be obtained. Therefore, the number of patients who continued to take medications was used as one of the indicators for comparing the efficacy between the groups. Even though this method introduces some systematic bias, it still provides valuable insights into the difference in treatment effect between the two groups.

The Visual Analog Scale (VAS) was used to evaluate the level of pain, with 0 indicating no pain and 10 indicating maximum pain. The patient selected a number between 0 and 10 on a caliper to indicate the intensity of their pain.

The Athens Insomnia Scale (AIS) (11) was used to assess sleep quality. An AIS score of 6 was considered insomnia, scores between 4 and 6 suggested suspected insomnia, and scores below 4 indicated no sleep disturbance.

The Generalized Anxiety Disorder-7 item (GAD-7) (12) scale and the Patient Health Questionnaire-9 items (PHQ-9) (13) were used to evaluate anxiety and depression, respectively. The scores ranging from 0 to 4 indicated normal levels, while the scores ranging from 5 to 9 indicated symptomatic levels, with higher scores indicating more severe symptoms, up to a maximum score of 27.

Follow-up mainly consisted of outpatient visits, supplemented by telephone and online follow-ups. Patients were asked to fill out the evaluation forms honestly. Follow-up sessions were scheduled before operation, 1 week, 1 month, 3 months, 6 months, and 12 months post-operation.

SPSS 23.0 statistical software was used for analysis. Data were expressed as mean ± standard deviation. A t-test was performed to measure the data such as age, height, etc. Scores from the VAS, AIS, GAD-7, and PHQ-9 were compared between the two groups using repeated-measures analysis of variance. The chi-squared test was performed to compare categorical data such as sex, hypertension, diabetes, and oral medications. A P-value of < 0.05 was considered statistically significant.

Twelve months after surgery, the number of patients requiring oral medication (pregabalin or opioids) in the PHN group was 3.3 times greater than in the AHN group, indicating a statistical difference (P = 0.001). There were no statistically significant differences in terms of patients' basic information, including sex, age, height, weight, BMI, VAS, smoking, drinking, hypertension, diabetes, and insomnia, between AHN group and PHN group (see Table 1).

The VAS scores of both the AHN and PHN groups were significantly lower than those before the procedure (P < 0.001). In addition, the VAS score of the AHN group gradually decreased over time, while the PHN group's VAS score gradually increased from 1 week to 12 months after surgery (P < 0.001). The difference between the two groups gradually increased after 1 month (Figure 3). The results of repeated-measures analysis of variance showed a statistically significant time effect between the two groups (F = 1,872.990, P < 0.001), indicating that VAS scores in both groups significantly reduced over time compared with those before surgery. Time^*group effect was also statistically significant (F = 164.289, P < 0.001), indicating that the decrease in VAS scores in the AHN group was significantly greater than that in the PHN group.

AIS, GAD-7, and PHQ-9 scores significantly decreased after surgery compared to preoperative scores (P < 0.001). In the AHN group, AIS, GAD-7, and PHQ-9 scores decreased over time following the procedure. In contrast, the PHN group's AIS, GAD-7, and PHQ-9 scores gradually increased at all time points post-procedure. From 1 to 12 months after surgery, the differences between the two groups became significant (P < 0.001) and increased over time (Figures 4, 5A, B).

Repeated-measures analysis of variance of AIS, GAD-7, and PHQ-9 scores yielded similar results to those of VAS. The time effect has a statistical difference (F = 3,413.527, P < 0.001; F = 2,366.545, P < 0.001; F = 2,384.951, P < 0.001), and the time^*group interaction effect was also significant (F = 228.316, P < 0.001; F = 266.207, P < 0.001; F = 392.077, P < 0.001). This indicates that there were significant differences in AIS, GAD-7, and PHQ-9 scores between the two groups before and after surgery. Moreover, there were significant differences between the groups (P < 0.001), with the AHN group showing a more substantial decrease in AIS, GAD-7, and PHQ-9 scores compared to the PHN group.

Our study has some limitations. As a retrospective study, it may introduce some bias in the data and lack the rigor of multicenter randomized controlled studies. Currently, there is no international standard for setting the parameters of pulsed radiofrequency therapy. Conducting a multicenter, prospective, double-blind controlled study is the next step worth pursuing.