1. Clinical data
A total of 60 patients that underwent radiofrequency thermocoagulation therapy for postherpetic neuralgia in the pain department of our hospital from January 2013 to November 2017 were retrospectively reviewed. Among them, 34 males and 26 females were present, aged from 49 to 93 years, with an average age of 72.50 ±9.43 years. Radiofrequency thermocoagulation of spinal dorsal root ganglion was performed by the same doctor with sufficient clinical pain management experience.
2. Inclusion and exclusion criteria
2.1 The following inclusion criteria were used: (1) The subjects met the clinical diagnostic criteria of post-herpetic neuralgia; (2) The age of the subjects was higher than and/or equal to 18 years; (3) The diseased region of the herpes zoster only involved the unilateral trunk nerve, that is, the thoracic 1-12 nerve; (4) The subjects' pain numerical score (NRS) was higher than 4 when they were admitted to the hospital; (5) The course of the herpes zoster disease lasted more than 3 months; (6) During hospitalization, the subjects underwent radiofrequency thermocoagulation of the spinal dorsal root ganglion under the guidance of the CT scan (Subsidiary Table 1.); (7) All the subjects agreed and received follow-up by telephone.
2.2 The following exclusion criteria were used: (1) Patients with a history of malignant tumors; (2) Patients receiving immunosuppressive therapy; (3) Uncooperative patients with mental illness, mental retardation and confusion; (4) Patients with severe liver, kidney, heart and lung diseases; (5) Patients who had received a history of invasive treatment prior to operation; (6) Patients who withdrew from the operation due to lack of cooperation with the surgeon during the operation; (7) Patients who received other invasive treatment or other surgeries following the operation; (8) Patients who lacked basic information and could not be followed up following the operation.
The patients were selected according to the inclusion and exclusion criteria and all patients were divided into the bipolar group (DCRF group, n=24) and the unipolar group (CRF group, n=36) by reviewing their intraoperative imaging data.
3. Surgical methods
The patients entered the CT treatment room and were laid at the prone position on the treatment bed. A vital sign monitor was used to connect the monitor’s blood pressure, heart rate and oxygen saturation. A positioning grid was placed at the patient's preoperative mark and fixed with adhesive tape (Fig 1a. 2a). A single CT scan was performed and following the scan, the puncture route was designed using the CT software (Fig 1b. 2b-1. 2b-2). After using the positioning grid to determine the puncture site, local infiltration anesthesia was performed with 2% lidocaine at a volume of 0.5 ml. Under the guidance of CT, the puncture needle was used to create a puncture along the preset angle and a path to the specified position. In the CRF group, a single puncture needle was punctured to a pre-designed target (Fig 1c). In the DCRF group, two puncture needles were punctured from the different angles to the pre-designed target (Fig 2c). Following completion of the initial puncture, a CT scan was performed again to confirm the puncture site. Further adjustment of the direction of the needle was performed to the outlet of the nerve root at the ventral superior edge of the intervertebral foramen in the affected area (Fig 1d. 2d). Following successful positioning of the puncture needle, the RF device was connected and the following tests were performed: (1) the sensory electrophysiological test was carried out under 50 hz and 0.1 ms and the current threshold inducing abnormal pain sensation was observed to judge the accuracy of the puncture site and record the current (mA) at this time. (2) Subsequently, the exercise electrophysiological test was carried out under 2 hz and 1.0 ms in order to observe the current threshold that could make the muscle beat in the area, which was innervated by the dorsal root ganglion and to record the current (mA) at the same time. Subsequently, the tip position was adjusted again until the movement and sensation areas were completely covered, without affecting the normal area. Finally, the radio frequency parameters were set. The parameters of the patients in the CRF and DCRF groups were both 95℃ and 300 seconds. During the operation, the reaction of the patients was observed and the incidence of the complications was assessed. A record from all the patients was made. At the end of the operation, the puncture needle was removed, sterilized and bandaged with aseptic dressing. The patients were observed for 15 min and subsequently returned to the ward following confirmation of their vital signs being normal.
4. Observation and follow-up
The preoperative data included age, sex, pain course, pain location and preoperative pain numerical rating scale22 (NRS), as well as the NRS score 1 day following the operation. These data were obtained by the inpatient information system, which is termed HTShell system 3.0. The postoperative data included NRS, pain relief, operative complications and side effects at 3 months, 6 months, 1 year and 2 years, all of which were evaluated by telephone follow-up. The medical staff in the non-operation group followed up the patients by telephone.
Pain was measured with a pain numerical rating scale, ranging from 0 (no pain) to 10 (the most unbearable pain). The degree of pain relief was evaluated according to the curative effect of the patient 2 years following the operation. The curative effect was divided into 4 grades (a, b, c, d) according to the ratio of (difference between preoperative NRS and postoperative NRS) / preoperative NRS. The following grades were defined as follows: (a): Complete Relief (CR), pain relief more than 75%; (b): Partial relief (PR), pain relief 50 to 75%; (c): Mild relief (MR), pain relief 25 to 50%; (d): Unresponsive Relief (NR), pain relief less than 25%. The total effective rate (%) was defined by the following equation: [(CR + PR + MR)/n]×100% and the marked rate (%)= [(CR + PR)/n]×100%.
In addition, the incidence of the complications, including short-term pneumothorax, such as hematoma, infection and spinal cord injury and the long-term complications, such as numbness in the corresponding innervated areas and abdominal dilatation were recorded. Moreover, the incidence of numbness and abdominal distension was calculated in the affected area.
5. Power of the study
The analysis of the clinical data of the patients suggested that the marked rate of 2 years after the surgery was 53.33% in the CRF group and 94.74% in the DCRF group. The power of the study was estimated to 90%, with 95% confidence interval and a 2-sided type I error of 5%. Therefore, the present study required 19 patients in each treatment arm. To compensate for patients who may have been lost to follow-up, 60 patients were reviewed for the two groups. Among them, 36 patients were included in the CRF group and 24 patients in the DCRF group.
6. Ovalbumin in vitro test
In the in vitro ovalbumin test, the puncture needle (Subsidiary Tab 1.) and radio frequency electrode (Subsidiary Tab 1.) used in the clinic were completely immersed in the culture medium, so that the active tip of the needle was wrapped by ovalbumin (Subsidiary Fig 1a. 1b). In the CRF group, the electrode was placed in parallel and connected to the output socket of the radio frequency generator. However, in the DCRF group, two electrodes were placed in parallel and connected to the output socket of the radio frequency generator and the distance between the two electrodes was gradually adjusted according to the experimental requirements. When the radio frequency generator was operating, the tip temperature was kept at the target temperature of 95℃. Following heating, the electrode was cooled to room temperature. The image of thermal coagulation of ovalbumin was obtained directly on the side and directly above the active tip of the puncture needle. A measuring ruler was placed for reference (Subsidiary video 1. 2). In the DCRF group, the distance between the two electrodes was set at 2, 3, 4, 5, 6, 7 and 8 mm. The length, width, height and final tissue weight (mg) of the thermal coagulation in the CRF and DCRF groups were recorded by manual measurement of thermal coagulation at different intervals and different time points (Fig 3a. 3b. 3c. 3d). Therefore, the effects of bipolar distance and heating time on the size of coagulation were analyzed further.
7. Statistical analysis
The SPSS25.0 (Subsidiary Tab 1.) was used for statistical analysis. The frequency was used as the main variable for the classification of the groups. The normality of the distribution was tested by the Kolmogorov-Smirnov test. The variables of the non-normal distribution were presented by the median (Quartile spacing) and were compared by the Mann-Whitney U test. The variables of the normal distribution were analyzed and compared by the independent sample T test and the values were expressed as mean ± standard deviation (`X±SD). The analysis was performed using the Pearson's chi-squared or the Fisher exact tests as appropriate. Bilateral P < 0.05 indicated that the differences was statistically significant.