Introduction
Pudendal neuralgia was first described in 1987 by Amarenco et al. Also known as Alcock’s canal syndrome, cyclist syndrome, or pudendal nerve entrapment syndrome, it affects both men and women and presents as pain in the dermatomal distribution of the pudendal nerve, including the penis, scrotum, vulva, clitoris, perineum, and rectum. This condition is often misdiagnosed or unrecognized by the vast majority of physicians, including pelvic pain specialists. The prevalence of pudendal neuralgia is unknown, but Spinosa et al . state an incidence rate as high as 1% of the general population, with women being more affected than men.
Etiology and Pathogenesis
The pudendal nerve is derived from the ventral rami of the second, third, and fourth sacral spinal nerves. , The nerve passes through the piriformis muscle, where it is joined with the pudendal artery and vein. This neurovascular bundle travels together between the sacrospinous and sacrotuberous ligaments ( Fig. 7.1 ). As the pudendal nerve exits and reenters the pelvis, it is contained within the pudendal canal. The pudendal nerve divides into multiple branches including the inferior anal nerve, perineal nerve, and dorsal nerve of the penis. ,
The pudendal nerve carries sensory, motor, and sympathetic fibers. The inferior anal nerve provides innervation to the external anal sphincter, distal anal canal, and the anal skin. The perineal nerve divides into posterior labial (female), scrotal (male), and muscular branches. The muscular branch provides innervation to the superficial transverse perineal muscle, bulbospongiosus, ischiocavernosus, deep transverse perineal muscle, sphincter urethrae, anterior portion of the external anal sphincter, and levator ani. The dorsal nerve of the penis/clitoris is the terminal branch of the pudendal nerve and provides sensory innervation to the respective male and female genitalia. ,
Pudendal neuralgia can arise from multiple mechanisms ( Table 7.1 ). Compression is the most common cause of nerve injury and may be transient or permanent. The degree of injury is mainly affected by the duration of pressure applied to the perineum and can occur at several locations along its course. Prolonged sitting or repetitive impact often leads to mechanical compression, causing entrapment at the sacrospinous or sacrotuberous ligaments. Pelvic floor muscle spasms or scar tissue from trauma may also result in nerve entrapment.
| Pelvic Surgery | Prolonged Sitting | Infection |
| Vaginal childbirth | Constipation | Malignancy |
| Traumatic fall | Excessive masturbation | Anal intercourse |
| Repetitive cycling | Pelvic radiation | Herpes zoster |
| Nantes Essential Diagnostic Criteria ∗ | ||
| Pain in the territory of the pudendal nerve: From the anus to the penis or clitoris : this criteria excludes pain located in the gluteal, sacrum, or coccygeal regions. The pain may be located superficially in vulvovaginal or anorectal regions. | ||
| Pain is predominantly experienced while sitting: while sitting the pain is from the increased pressure placed on the nerve. For patients with progressed pudendal neuralgia, the pain can become constant and present even when standing. | ||
| Pain does not wake the patient at night: perineal pain does not usually cause patients to wake up at night. Pudendal neuralgia can cause frequent awakenings at night due to the other associated symptoms including increased urinary frequency. | ||
| Pain with no objective sensory impairment: if the patient presents with perineal sensory deficit then a lesion of the sacral nerve roots or sacral plexus is possible and may also include sphincter motor disorders. It has been hypothesized that due to anatomic location of many nerves coursing closely together, there can be sensory impairment in areas near the regions innervated by the pudendal nerve. | ||
| Pain is relieved by diagnostic pudendal nerve block: local anesthetic infiltration of the pudendal nerve reduces pain dramatically. Even though it is listed as an essential criterion, there is the possibility that it can also relieve pain related to any perineal disease or nerve lesions located distal to the site of infiltration. | ||
∗ From Hibner M, Castellanos M, et al. Glob Libr Women’s Med , (ISSN: 1756–2228) 2011; doi:10.3843/GLOWM.10468.
Direct nerve injury can occur from excessive stretching or transection of the nerve, as seen during vaginal deliveries, pelvic surgeries, and traumatic falls. Pudendal nerve injury is often observed after corrective procedures for pelvic organ prolapse, with many patients reporting symptoms of pudendal neuralgia immediately postoperatively. , Less common causes of pudendal neuralgia include infection, tumor growth, pelvic radiation, or immunological processes. Herpes zoster has been shown to cause pudendal neuralgia due to herpetic inflammation.
Lastly, severe pudendal neuralgia can develop into complex regional pain syndrome (CRPS), which is a dysfunction of the peripheral and central nervous systems that are manifested by sensory and motor signs/symptoms such as burning pains, swelling, muscle spasms, and trophic changes among others. , , Traditionally, thought of as a dysfunction that occurs predominantly in the extremities, it is believed that pudendal neuralgia may progress in its symptomatology and develop into CRPS. This may lead to a more complex treatment course, given that many of the signs and symptoms are irreversible if left untreated.
Clinical Features
Patients with pudendal neuralgia typically complain of perineal and rectal pain, often describing a foreign body sensation as if they are continuously sitting on an object. , Moreover, the pain may be unilateral or bilateral in nature. They may also have symptoms at the urogenital or anal regions depending on where along the course in the pelvis the nerve is affected. In females, these areas include the vulva, vagina, clitoris, and labia. For males, the glans penis and scrotum (excluding testes) can be affected. ,
Neuropathies are typically described as a burning sensation with associated numbness or a sense of heaviness. , The pain can also exhibit sharp or aching features. Peripheral and central sensitization, as seen with features of increased sensitivity to painful stimuli (hyperalgesia) or pain with nonpainful stimuli (allodynia), are common among patients. , Pain is often provoked by movement and sitting, especially while driving or using a bicycle. Patients may report relief with standing and sitting on a toilet or donut cushion, which provides relief by reducing the pressure applied at the ischial tuberosities. As the disease progresses, patients can develop constant chronic pain that is also present in the standing position. , A small percentage of patients can also exhibit vague neuropathic pain symptoms in the posterior thigh and lower abdomen that is not an area in the pudendal nerve distribution. The pain in these regions is usually due to muscle spasms or referred somatic pain , , , , .
Patients may present with dysuria, dyschezia, dyspareunia, and pain with ejaculation. , , A subset of patients may experience restless genital syndrome, causing persistent sexual arousal that is painful. , Patients can also develop fecal incontinence from decreased sphincter tone. Urinary frequency and urgency have been noted and can mirror symptoms of interstitial cystitis. , ,
Diagnosis
Pudendal neuralgia is primarily a clinical diagnosis. Developed in 2006, the Nantes criteria describe the diagnostic components for pudendal neuralgia by entrapment ( Table 7.2 ). , These components have been validated, and patients meeting all the criteria have demonstrated better outcomes from decompression surgery compared to those who partially meet them. , The criteria were formed to limit the misdiagnosis of pudendal neuralgia. The five essential components are as follows: (1) pain in the distribution of the pudendal nerve, (2) pain predominantly while sitting, (3) pain does not wake up the patient during the night, (4) pain with no objective sensory impairment, (5) pain is relieved with a pudendal nerve block. ,
| Nantes Diagnostic Criteria for Pudendal Nerve Entrapment a | Exclusion Criteria |
|---|---|
| Pain in the anatomical territory of the pudendal nerve | Purely coccygeal, gluteal, hypogastric pain |
| Pain worsened with sitting | Exclusively paroxysmal pain |
| Patient is not woken at night from the pain | Exclusive pruritus |
| No objective sensory loss on physical exam | Imaging abnormalities able to account for the pain |
| Analgesic relief with pudendal nerve block |
Imaging: Doppler ultrasound is a relatively low-cost diagnostic imaging modality that can be a useful diagnostic tool. As the neurovascular bundle travels together, it is believed that compression of the nerve may lead to compression of the pudendal vein; Doppler technology should be able to assess for any changes in venous flow. High-frequency ultrasound can also assist with identifying other signs of nerve inflammation and compression, such as edema and any flattening of the nerve, respectively. Functional magnetic resonance imaging (MRI) can be performed to assess nerve integrity, though it has not been shown to be accurate enough to diagnose pudendal nerve compression and is viewed as experimental. Nonetheless, MRI can evaluate the spinal cord and nerve roots for any compressive pathologies as well as tumors or cysts that may be the source of pain , .
Nerve conduction studies: Pudendal neuropathy can be measured with sensory-evoked potentials, motor-evoked potentials, and pudendal nerve terminal motor latency testing (PNTML). PNTML involves applying an impulse through the vagina or rectum at the ischial spine. The impulse time is measured as it travels through the perineal muscles, and if latency is present, pudendal neuropathy is likely to be diagnosed. , PNTML values, however, are subject to high variability in patients who have undergone previous pelvic surgery or have a history of vaginal delivery due to stretching of the pelvic floor muscles. PNTML is also subject to substantial operator variability, which can lead to subject inconsistencies.
Pudendal nerve block, botulinum toxin injections: Diagnostic block not only aids in the diagnosis of the neuralgia, but also serves as a treatment option by injecting local anesthetic and steroid around the pudendal nerve to relieve pain. The block can be performed with or without imaging, which is discussed in the Treatments section. , Diagnostic block should provide pain relief within an hour for local anesthetic administration. To discern whether a patient’s symptoms are due to nerve injury or compression from pelvic muscle dysfunction, botulinum toxin injections at the respective pelvic floor muscles may be performed.
Physical Exam Findings
Physical exam of the patient should include a detailed examination of the patient’s back, abdomen, and pelvic floor muscles with an emphasis on any obvious signs of infection, palpable masses, lacerations, or skin erythema. Natal cleft livedo reticularis or cutis anserine skin changes can be seen in patients who develop CRPS due to pudendal neuralgia. , , Other potential signs include changes in skin color/temperature/texture, allodynia, and hyperalgesia.
Palpation of the coccygeal muscles, obturator internus, levator ani, psoas major and abdominal muscles should be assessed for tenderness and muscle spasms. A neurological examination should also be performed to include sensation to touch and pinprick. Painful palpation is common along the distributions of the pudendal nerve, including the clitoris or glans penis, posterior labia or posterior scrotum, and the posterior perianal skin , , .
The most common physical exam finding is reproducible pain, or a positive Tinel’s sign, when pressure is applied to the pudendal canal and ischial spine where the sacrospinous ligament inserts. Tinel’s sign is usually described as a numbing or tingling sensation when palpation or percussion of a certain nerve is performed. There can also be a positive Tinel’s sign when percussing the dorsal branch of the pudendal nerve affecting the clitoris or glans penis. , , In many cases of pudendal neuralgia, patients do not present with neurological deficits. ,
Treatment
Along with lifestyle modifications, the mainstay treatment for pudendal neuralgia is conservative management with pharmacologic and physical therapy. When these measures are unable to provide adequate pain relief, an interventional approach with injections and surgery may be considered. A multimodal approach to pudendal neuralgia is often required. , ,
Lifestyle modifications: Lifestyle modifications should be implemented immediately to avoid additional injury or worsening of symptoms. Provocative exercises or activities that exacerbate pain should be stopped. If pain is present with prolonged sitting, modifying position, or avoidance of sitting should take precedence. If patients are unable to avoid sitting, a cushion should be utilized to support the ischial tuberosities to decrease pressure on the pelvic floor muscles and pudendal nerve. Other modifications that should be employed include avoiding hard surfaces, cycling, hip flexion exercises, and squats focused on the lower body muscles. ,
Physical therapy: When applicable, physical therapy is centered on addressing pelvic floor muscle dysfunction. The majority of patients experience muscle spasms and muscle shortening of the pelvic girdle. Physical therapists work with patients on manual therapies to lengthen the pelvic muscles and work on strengthening exercises, stretching, biofeedback techniques, and trigger point release to relax the pelvic floor muscles. , ,
Medications : When lifestyle modifications and physical therapy fail to provide adequate relief, medical management can be considered. Neuropathic medications are a staple for the treatment of pudendal neuralgia. Gabapentinoids, such as gabapentin and pregabalin, are anticonvulsants that are used for a variety of other neuropathic pain syndromes and have both been used for the treatment of pudendal neuralgia; neither of these medications has been FDA-approved for this syndrome specifically. Additionally, tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors are other agents that have been shown to be beneficial in reducing neuropathic symptoms. , Muscle relaxants, such as cyclobenzaprine, tizanidine, and baclofen, are commonly prescribed for patients with a myofascial component to their pain. Nonsteroidal antiinflammatory drugs and paracetamol should also be used when appropriate.
Botulinum toxin injection : If physical therapy does not improve pelvic floor muscle dysfunction, then botulinum toxin injections into the pelvic floor muscles as an alternative treatment can be considered. Administration of 50–400 units of botulinum toxin have been reported in the literature. A concerning complication is accidental injection into the anal or urinary sphincter, which can lead to transient incontinence. Patient may resume physical therapy after 5–7 days. It is important to note that while effective in up to 67% of patients with pelvic floor dysfunction, the success rate of botulinum toxin injection is 30% when used for pudendal neuralgia specifically.
Pudendal nerve block: Pudendal nerve block injections serve as a diagnostic and therapeutic procedure. Injections can be performed using anatomical landmarks, fluoroscopic guidance, computed tomography (CT), or ultrasound. , Unilateral or bilateral injections are performed depending on the laterality of the patient’s pain. A combination of long-acting local anesthetic, such as bupivacaine, and corticosteroids are commonly used for the injectate.
When using the landmark technique in female patients, the transvaginal approach requires the patient to be placed in the lithotomy position. The ischial spine is palpated and the needle is guided toward the tip of the ischial spine. The needle is advanced through the vaginal mucosa until it reaches the sacrospinous ligament. With fluoroscopy or CT guidance, the patient is placed in the prone position and the needle is advanced to the tip of the ischial spine ( Fig. 7.2 ). The needle is slightly withdrawn after contact with the ischial spine is made and medication is administered after negative aspiration rules out intravascular injection.
