Pudendal neuralgia (PN) is a complex disease with various clinical characteristics, and there is no treatment showing definite effectiveness. This study is aimed at evaluating the clinical efficacy of ultrasound-guided high-voltage long-duration pulsed radiofrequency (PRF) for PN. Two cadavers (one male, one female) were dissected to provide evidence for localization of the pudendal nerve. Patients diagnosed as PN who failed or were intolerant in regular medication were screened for diagnostic local anesthesia block of the pudendal nerve before recruitment. Twenty PN patients were enrolled in this study. In the PRF procedure, the needle tip was inserted medially into the internal pudendal artery under ultrasound guidance. The position of the PRF needle tip was then adjusted by the response of the pudendal nerve to the electrical stimulation within the pudendal area (42°C, a series of 2 Hz, and 20 ms width pulses that lasted for 900 s). Alleviation of pain was assessed by the visual analogue scale (VAS) and sitting time pretreatment and on 7 d, 14 d, 1 m, 2 m, 3 m, and 6 m posttreatment in outpatient follow-up or by telephone interview. Two patients were lost due to intervention-irrelevant reasons. Patients showed significantly decreased VAS scores on 7 d after RFP, compared with pretreatment status (
Pudendal neuralgia (PN) refers to neuropathic pain in the pudendal nerve innervation region, which may occur in the entire perineal region or in one of its branches, and is often accompanied by symptoms such as rectal and anal foreign body sensation, distension, frequency and urgency of urination, and sexual dysfunction [
Radiofrequency has been used to treat pain for nearly a century. It is widely applied to regions including the head, neck, chest, waist, and sacral region [
Compared with other image-guided technology, ultrasound is playing an increasingly important role in pain diagnosis and treatment due to its advantages of radiation-free, convenient, and real-time positioning guidance [
Two adult cadavers (one male and one female) formalin embalmed and fixed were used (provided by the Human Anatomy Teaching and Research Department of the Basic Department of Naval Military Medical University). The cadaver specimens had intact pelvis and pelvic organs. The subcutaneous tissues and muscles of the buttock were opened layer by layer to expose the subgluteal space, the sacrospinous ligament, and its adjacent vessels and nerves. The anatomical relationship between the sacrospinous ligament and the pudendal nerve was confirmed.
Patients diagnosed as PN who received treatment were recruited from the pain center of Changhai Hospital from Sep 1, 2015, to Oct 31, 2016. The PN diagnosis was based on the Nantes criteria (Table
Diagnostic criteria for pudendal neuralgia (Nantes criteria).
Essential criteria | Complementary diagnostic criteria | Exclusion criteria |
---|---|---|
Pain in the territory of the pudendal nerve | Burning, shooting, and stabbing pain, numbness | Exclusively coccygeal, gluteal, pubic, or hypogastric pain |
Inclusion criteria are as follows: (1) aged from 18 to 80 years old and no sex limitation; (2) patients who were not satisfied with conservative treatment or intolerant to the side effects; and (3) be able to sign an informed consent form. Exclusion criteria are as follows: (1) patients with pelvic organic disease that may also cause pain in the pudendal region; (2) patients with malignant or autoimmune diseases that cause pain; (3) pregnant women; (4) patients with any coagulation disorder; and (5) patients who are unable to complete the outpatient or telephone interview.
Effective pudendal nerve block is an essential approach for the inclusion of patients. The patient was in the prone position, and a low-frequency curved-array probe (C251/1~5 MHz, Hitachi Noblus, Japan) was used to scan from the posterior superior iliac spine downwards to the transverse section of the ischial spine (Figures
Diagnostic block of the pudendal nerve under ultrasound guidance. (a) Position and direction of the ultrasonic probe. (b) Transverse section of the ultrasound image in the ischial spine. Red outline: sacrospinous ligament; yellow outline: ischium; white arrow: ischial spine. L: lateral; M: medial.
Internal pudendal artery presented in color Doppler. White arrow: ischium spine; red arrow: internal pudendal artery; blue arrow: internal pudendal vein. L: lateral; M: medial.
In the PRF procedure, the patient was placed in the prone position on a sterilized sheet with routine disinfection. A 20 G radiofrequency needle (Cosman) was used for puncture, and the puncture process was the same as the diagnostic block of PN (Figures
Procedure of pulsed radiofrequency. (a) The relationship between the location of the PRF needle and the position of the ultrasonic probe. (b) The track of the PRF needle and the position of the needle tip. Orange arrow: radiofrequency puncture needle; red arrow: internal pudendal artery; white arrow: ischium spine. L: lateral; M: medial.
In the sensory test (50 Hz), when the voltage was 0.3-0.5 V, the patient could feel the tingling sensation at the pain site, which indicated that the puncture needle tip was around the pudendal nerve. When the voltage was higher than 2 V in the motor test (2 Hz), the lower limb movement of the same side was not induced, indicating that the puncture needle tip was far from the sciatic nerve. During PRF, the radiofrequency instrument was set as the manual pulse treatment mode, and the RF parameters were set as follows: temperature 42°C, stimulation frequency 2 Hz, pulse width 20 ms, and duration 900 s; the field intensity began at 40 V and gradually increased until the patient has an intolerable abnormal sensation (such as burning sensation) in the pain site (the intensity was not more than 80 V to avoid nerve damage caused by high temperature). Patients with bilateral pain were treated with bilateral PRF. The procedure was performed with the radiofrequency therapeutic apparatus (Baylis, Canada).
Through outpatient or telephone follow-up, the pain intensity of patients was evaluated before intervention and on 7 d, 14 d, 1 month, 2 months, 3 months, and 6 months after high-voltage long-duration PRF treatment. The visual analogue scale (VAS) was applied for pain assessment, with 0 indicating no pain, 1-3 mild pain, 4-6 moderate pain, and above 7 severe pain. The patients’ maximum sitting time before the onset of pain (i.e., sitting time) was evaluated according to the assessment method and criteria of previous studies [
The measurement data were expressed in terms of
Two cadaver specimens (embalmed) were examined, including one Asian man (death age 76, height 172 cm, and BMI 25.7 kg/m2) and one Asian woman (death age 86, height 158 cm, and BMI 19.2 kg/m2).
As indicated by a previous study [
Anatomical study of the pudendal nerve in cadavers. (a) Pudendal nerve and its adjacent tissues. (b) Pudendal nerve and its branches of a male cadaver (dissection of the sacrotuberous ligament). (c) Pudendal nerve and its adjacent tissue in a female cadaver. STL: sacrotuberous ligament; SSL: sacrospinous ligament; IPA: internal pudendal artery; IGA: inferior gluteal artery; PN: pudendal nerve; SN: sciatic nerve; D: dorsal nerve of the penis; P: perineal nerve; R: inferior rectal nerve.
At the cross of the sciatic spine in the male cadaver, the pudendal nerve was 13 mm medial to the sciatic spine, and the internal pudendal artery was 6 mm lateral to the pudendal nerve. In the female cadaver, the pudendal nerve was 11 mm medial to the sciatic spine, and the internal pudendal artery was 6 mm lateral to the pudendal nerve (Table
Distance of the pudendal nerve to the sciatic spine and the pudendal nerve to the internal pudendal artery in the cadavers.
Distance between the pudendal nerve and the sciatic spine | Distance between the pudendal nerve and the internal pudendal artery | |
---|---|---|
Male | 13 mm | 6 mm |
Female | 11 mm | 6 mm |
A total of twenty patients were finally enrolled, including six males and fourteen females, aged 42~68 yrs (
Demographic characteristics of patients.
Characteristic | Content | Value |
---|---|---|
Numbers ( | 20 | |
Sex ( | Male | 6 |
Female | 14 | |
BMI | Range | 18.9-31.70 |
Age (years) | Range | 42-68 |
Pain site | Anus | 5 |
Genitals | 7 | |
Anus, genitals, and perineum | 8 | |
Unilateral and bilateral pain | Unilateral | 12 |
Bilateral | 8 | |
Baseline VAS (points) | Range | 5-9 |
Baseline of sitting time (min) | Range | 5-52 |
Duration of pain | <1 year | 5 |
1-5 years | 10 | |
>5 years | 5 | |
Pain characteristics | Stabbing pain | 5 |
Burning pain | 11 | |
Aching pain | 4 | |
Throbbing pain | 2 |
All the patients reported moderate or severe pain, with VAS scores of
Results of the visual analogue scale (VAS) before and after high-voltage long-duration pulsed radiofrequency (PRF) treatment. VAS significantly decreased on 7 d after treatment and remained steady till 6 months. There was no significant difference among all the time points after treatment (pretreatment vs. 7 d, 14 d, 1 m, 2 m, 3 m, and 6 m posttreatment;
As many patients were unable to come for each outpatient follow-up due to intervention-irrelevant reasons (e.g., lived too far away from the center), part of the assessments was completed under the guidance of the same physician through telephone interview. Compared with pretreatment (
Comparison of sitting time before and after pulsed radiofrequency treatment. The sitting time significantly increased since day 7 after treatment (pretreatment vs. 7 d,
No serious adverse event was reported. No infection occurred following PRF. One patient reported ipsilateral involuntary convulsion of the lower extremity immediately after treatment and recovered within 12 h. Six patients complained of pain at the puncture site, which alleviated shortly with the application of nonsteroidal drugs. Three patients reported mild skin herpes in the perineum within 3 days after treatment and recovered thereafter, which was considered irrelevant to the intervention (Supplement Table
The etiology of PN is complex, and the mechanism is largely unclear. It may be due to the entrapment and mechanical injury of the pudendal nerve. The common entrapment sites are the sciatic foramen and pudendal canal between the sacrotuberous ligament and the sacrospinal ligament, especially the sciatic spine [
For these reasons, conservative treatment (e.g., oral medicine, nerve block therapy, and physical therapy) is usually ineffective. With the continuous development of image-guided technology, interventional treatment has been increasingly performed by clinicians, especially by pain practitioners. Interventional treatment (such as nerve block, radiofrequency, and electrical stimulation treatment) has been applied in the treatment of PN [
Radiofrequency technology is a novel technology to treat chronic pain. Traditional continuous radiofrequency technology damages nerves to treat pain in the dominant area, which would inevitably lead to permanent nerve injury and serious side effects. Compared with traditional continuous radiofrequency thermocoagulation technology, pulsed radiofrequency is a nonneurodegenerative radiofrequency technology. The temperature of the electrode tip does not exceed 42°C, which will not cause irreversible tissue damage, in which situation the sensorimotor functions of the nerve could be largely preserved.
However, the underlying mechanism of pulsed radiofrequency in the treatment of neuropathic pain is mostly unknown. Some studies suggested that low-temperature pulsed radiofrequency can form a field effect around the lesion, thus regulating the transmission of pain signals [
Anatomically, the pudendal nerve goes tortuously and is largely varied. A study showed that before entering the pudendal canal, the branch of the pudendal nerve, the inferior rectum nerve, often runs inward and downward [
With the internal pudendal artery companied, the pudendal nerve is located on the surface of the sacrospinal ligament. When it goes down into the pudendal canal, its branches are more dispersed, and its relative location to the internal pudendal artery may be varied. Therefore, the pudendal nerve is more accessible in the transverse section of the sciatic spine. Previous studies suggested that the pudendal nerve is adjacent to the sciatic nerve above the cross-section of the sciatic spine, which indicated that the sciatic nerve and even the sacral plexus could be involved if penetrating above the cross-section of the sciatic spine. Therefore, punctuation is recommended to locate at the entrance of the pudendal nerve canal. This provided important information for improving ultrasound-guided treatment for PN [
Brusciano et al. reported a novel approach, the dynamic transperineal ultrasound (DTU), in the assessment of the pudendal nerve motility [
The present study suggested that high-voltage long-duration PRF treatment can alleviate the pain of patients with pudendal neuralgia and improve their quality of life by prolonging the sitting time without obvious severe adverse events. Ultrasound-guided PRF could be a safe and rewarding treatment for PN patients.
The data used to support the findings of this study are available from the corresponding author upon request.
All authors claim that there are no conflicts of interest.
Feng Ji and Shuzhuan Zhou contributed equally to this work.
This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 82074288).
Supplement Table 1: information of all patients. Supplement Table 2: adverse events. Supplement Table 3: follow-up assessments of all patients.