Pudendal neuralgia (PN) is a chronic, severe pain in the vaginal, vulvar, anal canal, and perineal regions without organic pathology that is difficult to diagnose and treat definitively, and was proposed by Boisson et al. as early as 1966, followed by Neill and Swash, who suggested that spontaneous chronic anal perineal pain may originate from pudendal neuralgia. The incidence of pudendal neuralgia is unclear, and it is a rare condition that affects both men and women. It usually develops between the ages of 40 and 70 years. The typical female patient presents with pain in the labia, perineal area or anorectal area, while the male presents with pain in the penis, scrotum and perineal area. The pain is worse in a sitting position, relieved when standing, and disappears when lying or sitting on the toilet. Perineal neuralgia is often delayed or misdiagnosed, leading to unnecessary surgical procedures. Many gynecological conditions are also incorrectly diagnosed as pubic neuralgia because the etiology of the pain is unclear. Pain can also be caused when the pubic nerve is damaged after a pelvic fracture or surgical procedure. This article provides a comprehensive discussion of the anatomical basis of pubic neuralgia in women, symptoms, diagnostic criteria, useful diagnostic tests and the current status of treatment research.
1.Anatomy
The pubic nerve originates from the anterior horn neurons of the sacral segment of the spinal cord (S2-4), also known as Onuf’s (Onufrowicz’s) nucleus, and then travels medially and caudally to the sciatic nerve, and enters the gluteal region through the foramen magnum of the sciatic bone via the inferior foramen of the pyriform muscle. The pubic artery accompanies it and the veins surround it in a plexus pattern. The pubic nerve trunk crosses the sacrospinous ligament close to the sciatic spine, and at this level the pubic nerve lies between the ventral sacrospinous ligament and the dorsal sacral tubercle ligament; in rare cases, the pubic nerve travels in the sacral tubercle ligament cleft. The nerve trunk then enters the perineal region ventrally, medially, and caudally through the sciatic foramen and enters the subanal levator muscle at the overlap of the internal myofascia of the closed foramen to form the pubic canal (Alcock’s canal). In most cases, three neurovascular bundles originate in the canal: the anal nerve, the perineal nerve, and the dorsal clitoral nerve.
The anal nerve innervates the perineal area and communicates with the perineal branch of the posterior femoral cutaneous nerve, the terminal branch of which is the labyrinthine nerve. It can sometimes originate directly from the sacral plexus or before the pubic nerve enters the pubic canal.
The perineal nerve has a motor branch and two superficial sensory branches (medial and lateral branches of the posterior labial nerve) that innervate the perineal area and ipsilateral posterior labia majora sensation, as well as the deep and superficial transverse perineal muscles, bulbocavernosus muscle, urethral bulbocavernosus muscle, urethral sphincter and anal levator muscle. This branch originates from the posterior part of the pubic canal.
The dorsal penile (clitoral) nerve is the terminal branch of the pubic nerve at the level of the pubic symphysis, which is the afferent nerve for clitoral sensation.
Although the anatomy of the branches of the pubic nerve is well dissected, there are many variations within the sciatic fossa and within the pubic canal. Since its branches mostly travel on the surface of the pelvis, they are vulnerable to injury.
2.Symptoms
Neuralgia in the pubic area is often manifested as pain in the vagina, labia, mons pubis and clitoris area in women. The pain and sensory abnormalities can spread to the groin area, inner thighs, buttocks and abdomen, and can involve one, several or all of these areas. It usually starts in one area and worsens progressively with unilateral attacks. It can also be bilateral, and one side may be distinctly different from the other. The pain is severe, sharp, sometimes burning, and often not relieved by analgesics.
Pain has been reported to be significantly worse in the sitting position, and many patients have pain in the lying position and have difficulty sleeping. Patients may be awakened by concomitant symptoms (e.g., urgency to urinate) and are rarely awakened by pain. Pain can be relieved to varying degrees by sitting on an empty lap pillow or on the toilet, which relieves pressure on the nerves. Sensory sensitization of the skin in the area may occur. The clinical presentation of pubic neuralgia can reflect the type of nerve damaged (motor, sensory, voluntary). The patient’s history often progresses from an automatic recovery process to a chronic, progressive exacerbation process that affects the patient’s daily life.
Accompanying symptoms may include constipation, painful defecation, delayed urination, urinary frequency, urinary urgency and sexual dysfunction.
3.Pathophysiological pathogenesis
It is not clear, but the basic etiological hypothesis is that it is caused by injury caused by stretching or compression of the pubic nerve. It is usually unilateral and rarely bilateral. Causes of nerve injury include: sciatic spine fractures due to tumors, compression of the falciform portion of the sacral tubular ligament, compression during transcatheter Alcock’s canal, bicycling, herpes simplex infection, compression by tumors or endometriosis, chemotherapy for rectal cancer, constipation, and stretching of vaginal prolapse.
Medically induced injuries include nerve blocks in the pubic area, effects on nerves and blood flow during surgical exploration of the pelvic cavity, and injury to nerves from muscle strains during lower extremity surgery. Since the pubic nerve travels lateral to the sacrospinous ligament, knots tied laterally to the ligament during sacrospinous ligament fixation for vaginal prolapse, for example, tend to compress and injure the nerve.
4.Diagnosis
(1) The diagnosis of pubic neuralgia is an exclusionary diagnosis, that is, it can be suggested by excluding other causes of the same symptoms. ‘Urodynamique et dePelviPe?rine?ologie) was recognized.
Diagnostic criteria: (1) the pain is distributed in the innervated area of the pubic nerve; (2) the pain worsens further when sitting; (3) the patient does not wake up with pain at night; (4) there is no loss of sensation on physical examination; and (5) the pain is improved by a pubic nerve block. Exclusion criteria included paroxysmal sacrococcygeal, gluteal, or lower abdominal pain with pruritus or abnormal imaging findings . The difficulty in diagnosis is that all of these criteria are entirely subjective sensations and there is also a placebo effect or a false positive result of distal anesthesia with nerve blocks.
(2) Pubic nerve block
is considered to be the basic diagnostic method in the Nantes diagnostic criteria. After blocking the nerve with local anesthetics, if the pain is relieved then the nerve is proven to be agitated or damaged. However, there is a placebo effect for pubic nerve blocks and there are no specific indicators that the drug is acting on the pubic nerve. Pain from other perineal and vaginal causes of disease can also be relieved by pubic nerve blocks, and there can be positive responses to all types of nerve damage through drug penetration. A negative result likewise does not exclude the presence of pubic nerve pain, as there is no evidence that the drug has reached the site of pubic nerve damage.
(3) Laboratory tests
Vaginitis or urinary tract infection can be ruled out. In contrast, the clinical examination is usually normal in patients with pubic neuralgia. If there is sensory deficit suggestive of sacral nerve root, especially cauda equina, or sacral plexus injury, these proximal injuries usually do not cause pain and clinically manifest only as sensory-motor deficits, especially sensory deficits and sphincter motor dysregulation. The classic physical examination is to apply appropriate pressure in the rectum or vagina, which can replicate or worsen the pain.
(4) CT scan does not show the nerves and is not valuable in diagnosing pubic neuralgia, but is valuable in ruling out organ damage and finding the cause of nerve compression at the level of the lumbar spine (cauda equina syndrome, sacroiliac joint dysfunction, etc. are very similar to the symptoms of pubic neuralgia).
(5) MRI
It can also be used to rule out other organ injuries in the pelvis, and it can also show the course of the pudendal nerves in detail. Asymmetric swelling, distortion, or high signal of the pubic neurovascular bundle at the level of the Alcock canal or sciatic spine can be seen.
(6) Color ultrasonography aids in the diagnosis.
(7) Neurophysiological test
PNMLT is the administration of electrical nerve stimulation, followed by recording of the stimulation conduction velocity with special electrodes. A slower than normal nerve response (2.2m/s) indicates nerve damage. However, this test is not specific, as PNMLT is specific for demyelination, but not for nerve fiber damage, and only for motor nerves. There is no good way to test for sensory nerves that conduct pain. EMG and single-fiber EMG with latency testing provide a better picture of neuropathy, but only motor nerves can be assessed, and the procedure can also cause pain and discomfort. Neurophysiologic evaluation can measure anal reflex latency, bulbocavernosus reflex latency, somatosensory evoked potentials of the pubic nerves, and conduction velocity of the dorsal clitoral nerve. These tests can provide further insight into the condition of the nerves, but none is specific due to age and gender.
5.Treatment
(1) Conservative treatment
Conservative treatment includes behavioral changes, such as avoiding triggering behaviors (bicycling, hip flexion, etc.). Stretching exercises can reduce pain in a proportion of patients with pubic neuralgia such as cyclists. Actions such as bending over and touching the toes or holding the knees toward the chest in the supine position are effective Acupuncture is effective in some patients, but not in general. Low back massage may be effective. Medications such as gabapentin (an antiepileptic) and tricyclic antidepressants are mostly ineffective. If conservative treatment is not effective, invasive treatment is available.
(2) Minimally invasive treatment
(1) Nerve block
①Pubic nerve block
The earliest method of pubic nerve block was the transrectal route described by Mueller in 1908, in which the index finger was placed on the sciatic spine through the anal canal and a 10-cm puncture needle was used to inject local anesthetic through the colorectal fossa, and in 1954, Kohl advocated a more accurate transvaginal route. Due to the hypersensitivity of the perineal region, the injection often causes severe pain and some patients must be operated under general anesthesia. mcdonald and spigos used CT guidance to locate the sciatic spine more precisely. In their study, 26 female patients with pubic neuralgia underwent CT-guided pubic nerve blocks once a month for 5 consecutive sessions, and 16 patients (62%) experienced pain relief after treatment. In another report of CT-guided pubic nerve blocks, the puncture needle was positioned at the highest point of the sciatic spine, and all 25 patients were successfully blocked. More recently, a prospective study of 55 patients with MRI-guided pubic nerve blocks was reported, with a good result of 87% efficiency. It is clear that all three studies mentioned above lacked a control group and were insufficiently randomized.
The block is usually unilateral, or bilateral if the patient has bilateral symptoms. Frequent puncture injections of local anesthetic can also stimulate the nerve and trigger new pain. Patients usually begin to experience pain relief within minutes after a pubic nerve block, and the effect lasts for 4-6 weeks.
The use of nerve stimulators and ultrasound localizers has improved the accuracy of nerve blocks and reduced the number of complications.
The inferior hypogastric plexus block is located bilaterally in the anterior sacral promontory of the retroperitoneum from L5 to S1, near the point of bifurcation of the common iliac vessels, and is a continuation of the abdominal and lumbar sympathetic nerve chain on both sides, and innervates the pelvic viscera through the inferior hypogastric nerve. Plancarte et al. first described the inferior hypogastric plexus block in 1990, and several reports have now demonstrated that this plexus block is effective in treating advanced pelvic cancer pain, and is also effective in The pudendal nerve pain has also been shown to be effective in the treatment of pubic neuralgia.
These nerve blocks can be performed in weekly fractions or as a continuous block, with the latter having a more stable and long-lasting effect. NSAIDs can reduce the inflammation and expand the sliding space of the nerve. The mechanism of nerve block therapy: ① block the conduction pathway of nociception; ② block the vicious cycle of pain; ③ improve local blood circulation; ④ anti-inflammatory effect.
2） Pulsed radiofrequency
Pulsed radiofrequency has been reported to be used for the treatment of pubic neuralgia. In this report, a 41-year-old woman had sharp burning pain in the left buttock and perineal region for one and a half years and could not sit for more than 10 minutes. The pain was not relieved by sacroiliac joint, epidural, or pear muscle injections; morphine and gabapentin only slightly relieved the pain; the diagnostic pubic nerve block test was positive; pulsed radiofrequency treatment of the pubic nerve was given at a frequency of 2 Hz, pulse width of 20 μs, and 42°C for 120 seconds. The patient was able to sit for 4 to 5 hours after treatment, and other treatments were discontinued. The patient felt able to work after 5 months of follow-up, and after one and a half years, oral oxycodone could control the pain and tolerate sitting. No associated complications occurred. Although this is only one case report, it is significant. The effectiveness of pulsed radiofrequency for trigeminal neuralgia has been demonstrated, but the maintenance time is unstable, generally lasting only 3 months to 6 months.
3) Cryo-analgesia method
Cryoanalgesia is a special technique for pain relief by interventional means. The method destroys the nerve structure and causes Wallerian degeneration, preserving the myelin sheath and endothelium. Neuralgia in the pubic area is one of the indications for cryo-analgesia, but there is no literature to prove the effectiveness and safety of this method for treating neuralgia in the pubic area.
4) Spinal cord electrical stimulation
In 1906, sacral root stimulation (SRS) was first suggested for the treatment of urinary dysfunction. In 1965, Melzack and Wall proposed the gate theory of pain, which became the main mechanism of action of spinal cord stimulation (spinal cord stimulationSCS). The spinal cord is the center of pain regulation and integration, and pain signals are regulated in the spinal cord before they enter the higher centers, and the spinal cord responds to stimuli by opening and closing the “pain gates. When the gates are open, pain signals travel up the thalamic tract of the spinal cord to the hypothalamus, where the right limbic system produces slow pain perception. In 1967, Shealy et al. successfully implanted electrodes into the epidural to treat chronic pain. Many prospective and retrospective studies have now confirmed the effectiveness and safety of SCS in the treatment of chronic pain. Recently, studies have also been conducted for the treatment of pubic neuralgia.
5) Nerve destruction
Because the motor branch of the pubic nerve manages important physiological functions, it is generally not used for pubic neuralgia.
(3) Nerve decompression surgery
Surgical nerve decompression surgery is also an option when there is evidence of nerve compression and the pain is only partially relieved temporarily after nerve block. There are three commonly used procedures: transperineal, transgluteal, and trans-sciatic rectal fossa. The efficacy of the three modalities is similar 50% to 86%, but randomized controlled studies are lacking.