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Pudendal neuralgia diagnosis and treatment.

Pudendal neuralgia is an important but often unrecognized and undiagnosed cause of pelvic floor pain.

Its incidence is unknown, and there is relatively little data and scientific evidence in the literature on its diagnosis and treatment. However, I believe that a significant number of women who have burning pain in the vulva, clitoris, vagina, perineum, or rectum - including women who are diagnosed with interstitial cystitis, pelvic floor muscle spasms, vulvodynia, or other conditions - may in fact have pudendal neuralgia. Indeed, pudendal neuralgia is largely a diagnosis of exclusion, and such conditions often must be ruled out. But it should be suspected in women who have burning pain in any area along the distribution of the pudendal nerve. Awareness of the nerve's anatomy and distribution, and of the hallmark characteristics and symptoms of pudendal neuralgia, is important, because earlier identification and treatment appears to provide better outcomes.

Pudendal neuralgia is but one type of pelvic neuralgia; neuropathic pain in the pelvic region also can stem from injury to the obturator, ilioinguinal, iliohypogastric, or genitofemoral nerves, for instance. Most of the patients in our practice, however, have pudendal neuralgia caused by mechanical compression - what is referred to as pudendal nerve entrapment-rather than disease of the nerve.

The condition is sometimes referred to as cyclist syndrome because, historically, the first documented group of patients with symptoms of pudendal neuralgia was competitive cyclists. There is a misconception, however, that the condition only occurs in cyclists. In fact, pudendal neuralgia and pudendal nerve entrapment specifically may be caused by various forms of pelvic trauma, from vaginal delivery (with or without instrumentation) and heavy lifting or falls on the back or pelvis, to previous gynecologic surgery such as hysterectomy cystocele repair, and mesh procedures for prolapse and incontinence.

Pudendal neuralgia is multifactorial, involving not only compression of the nerve, for instance, but also muscle spasm and peripheral and central sensitization of pain. Treatment involves a progression of conservative therapies followed by decompression surgery when these conservative treatments fail. We have made several modifications to the transgluteal approach as it was originally described, and believe this approach affords the best outcomes.

Anatomy and Symptoms

The pudendal nerve originates in the S2-S4 sacral foramina, and divides into three branches - the inferior rectal nerve, the perineal nerve, and the dorsal clitoral nerve. The nerve innervates the clitoris, vulva, labia, vagina, perineum, and rectum. Pain can be present along the entire nerve, or localized to the sites of nerve innervation. Symptoms can be unilateral or bilateral, although with bilateral pain there usually is a more affected side. In most cases, patients will describe neuropathic pain - a burning, tingling, or numbing pain - that is worse with sitting, and less severe or absent when standing or lying down.

Initially, pain may be present only with sitting, but with time pain becomes more constant and severely aggravated by sitting. Many of my patients cannot tolerate sitting at all. Patients usually report less pain when sitting on a toilet seat, a phenomenon that we believe is associated with pressure being applied to the ischial tuberosities rather than to the pelvic floor muscles. Pain usually gets progressively worse through the day Patients often will report the sensation of having a foreign body, frequently described as a golf ball or tennis ball, in the vagina, perineum, or rectum.

Pain with urination and/or bowel movements, and problems with frequency and urgency, also are often reported, as is pain with intercourse. Dyspareunia may be associated with penetration, sexual arousal, or orgasm, or any combination. Some patients report feeling persistent sexual arousal. Occasionally, patients report having pain in regions outside the areas of innervation for the pudendal nerve, such as the lower back or posterior thigh. The presence of pain that radiates down the leg, for instance, should not rule out consideration of pudendal neuralgia.

Just as worsening pain with sitting is a defining characteristic, almost all patients also have an acute onset of discomfort or pain; their pain can be traced to some type of traumatic event. One of my recent patients, for instance, was in a gym class doing a lunge with barbells on her shoulders when her legs gave out and she experienced the start of continuous pain in her vulvar area. Many of our patients trace the onset of their symptoms to immediately after gynecologic surgery, particularly vaginal procedures for prolapse or incontinence. (The pain in these cases is frequently attributed to normal postoperative pain.) Some patients report a more gradual onset of symptoms after surgery.

The pudendal nerve can be compressed in various locations along its course. The nerve runs between the sacrospinous and sacrotuberous ligaments, for instance, and entrapment between these two ligaments is probably the most common cause of pudendal neuralgia. This is where the nerve is compressed by the suturing of mesh placed during prolapse/incontinence surgery. Another area of compression is Alcock's canal; entrapment here is characteristic of pudendal neuralgia following vaginal childbirth. Compression also can occur where the clitoral nerve continues underneath the pubic ramus to the clitoris; this is typically where the nerve is compressed by a bicycle seat.

Diagnosis

The most important element of the diagnosis of pudendal neuralgia is the history, particularly regarding the onset of pain, the location of pain, and the nature of symptoms. History and physical examination both are important for ruling out other reasons for pain, including vulvo-dynia, pelvic floor tension muscle spasm, and interstitial cystitis. A pelvic exam often will reveal significant tenderness in the pelvic floor muscles, especially in the area of the sacrospinous ligaments. Patients with pudendal neuralgia often have a trigger point - a place of maximal tenderness and pain - at the ischial spine. Palpation of this area to produce what's known as a Tinel's sign (with pain and symptoms) thus should be part of the exam.

Also key to diagnosis are computed tomography-guided blocks of the pudendal nerve. In our practice, we consider any degree of pain relief, for any duration of time after the block, as supportive of a diagnosis of pudendal neuralgia. Patients who do not experience immediate relief from a block are thought not to have the condition. These image-guided blocks must be performed by experienced interventional radiologists with a local anesthetic.

To date, there are no imaging studies that are reliable for diagnosis. Ongoing advances in magnetic resonance imaging (MRI) and magnetic resonance neurography (MRN) may make these modalities valuable in the future, but currently these techniques yield too many false-negative results. Pudendal nerve motor terminal latency, which measures the conduction velocity of electrical impulses, is not useful given a high rate of intra- and inter-observer variability and variations among patients who have had previous vaginal deliveries or pelvic surgery. Sensory threshold testing has questionable reliability.

Initial Treatments

The initial approach to pudendal neuralgia should be conservative. Surgical decompression is the treatment of choice in patients with likely nerve entrapment, but determining the likelihood and extent of entrapment is a process. First, time must be spent in trying to identify and address the factors causing pain, and in trying to break the vicious cycle that occurs when neuropathic pain causes spasm of the pelvic floor muscles, which in turn leads to increased compression of the nerve and subsequent increases in pain levels.

While there are no official treatment algorithms, we have found - based on available data and our experience in treating more than 500 patients with pudendal neuralgia - that particular therapies can lead to marked improvements for many patients. For some patients, especially those in whom bicycling or specific exercises initially caused the pain, avoidance of activities that worsen the pain, and other lifestyle modifications, can be helpful. Medical therapy with analgesics/pain management (such as oral pregabalin) and muscle relaxants also may be helpful for some patients. We have tried all kinds muscle relaxants and have found that a vaginal suppository combining diazepam and baclofen is superior.

The most important treatment modality, however, is pelvic floor physical therapy. Such therapy is key because many patients have significant muscle spasm and subsequent muscle shortening. Therapists who are specially trained to work with pelvic floor muscle dysfunction can address these and other problems largely through various hands-on techniques, exercises, stretching, and education. Therapists can be identified on the International Pelvic Pain Society's website, www.pelvicpain.org.

Botulinum toxin A (Botox) injections also are often a key part of therapy for patients with significant muscle spasm. In our practice, we administer approximately 200 units in 20 injections using a pudendal nerve block needle, under anesthesia. Not only does the treatment aid in muscle relaxation (thus increasing the patient's tolerance to physical therapy), it also helps to differentiate between pain caused solely by muscle spasm, and pain caused by nerve injury and muscle spasm.

While patients who do not have neuralgia whose pain is caused solely or almost solely by muscle spasm will benefit significantly more from Botox injections, some patients with pudendal neuralgia will benefit from occasional, repeated Botox treatment in lieu or surgical decompression therapy. Many of our patients have been receiving Botox injections every 3-4 months, for instance.

Similarly, many other patients get significant pain relief from CT-guided injections of the nerve. While an initial CT-guided injection of anesthetic and steroid serves both diagnostic and therapeutic roles, a second and third injection can be performed to deliver more steroid and anesthetic into the pudendal nerve canal (Alcock's canal) in a patient who responded to the first injection but whose pain has returned. Again, these injections must be performed by an experienced interventional radiologist in a CT scanner.

Injections are offered 6 weeks apart, but some patients have significant pain relief for 4-5 months, or even longer, after CT-guided nerve blocks. Patients who have long-term pain relief from CT-guided blocks will not be offered decompression surgery. One of our patients, for instance, is receiving nerve blocks every 8 months as part of her treatment.

Surgical Decompression

If patients do not have sufficient pain relief from conservative therapies (relief that enables them to return to normal daily function), surgical decompression of the nerve is indicated. An estimated 30%-40% of all patients with pudendal neuralgia will benefit from surgery.

Four different procedures have been described for decompressing an entrapped pudendal nerve: transgluteal, transischiorectal, transperineal, and endoscopic.

The transgluteal approach appears to be the most effective technique, allowing the best visualization of the pudendal nerve and the greatest extent of decompression along the length of the nerve. The main concern with this approach since it was originally described by Professor Roger Robert in Nantes, France, has been the required transection of the sacrotuberous ligament and the possible impact on stability of the sacroiliac joint. In our practice, however, we have made several modifications to the approach that minimize these concerns and, we believe, are improving recovery and outcomes.

The patient is placed in a prone jackknife position, and the electrodes of an NIMS monitor (Nerve Integrity Monitoring System; Medtronic, Minneapolis) are placed in the anal sphincter. An incision of approximately 7-10 cm in length is made across the gluteal region overlying the sacrotuberous ligament. The gluteus muscles are spread, with muscle fibers separated longitudinally, and once the ligament is reached, it is transected at its narrowest point.

The pudendal nerve then can be identified immediately below the ligament with use of a surgical microscope and the NIMS. When the surface of the nerve is touched, we are alerted by the NIMS monitor (part of the nerve runs to the anal center). In some patients, the pudendal nerve may actually be attached to the anterior surface of the sacrotuberous ligament.

The nerve is then decompressed along its entire length, from the piriformis muscle and as close as possible to the spinal cord, to the distal Alcock's canal. Neurolysis is performed along each of the nerve's branches - the inferior rectal nerve, the perineal nerve, and the dorsal clitoral nerve - until the nerve is completely free. In our practice, we most often find the nerve entrapped between the sacrospinous and sacrotuberous ligaments, which form a sort of "V" in the pelvis. Because the sacrospinous ligament does not serve any anatomic purpose, I transect the ligament so that I can transpose the pudendal nerve anteriorly to give it more room.

Repair of the sacrotuberous ligament was not traditionally performed as part of the transgluteal approach, but we believe that repair is important for stability of the sacroiliac joint. Until recently, we used a graft of cadaver tendon to repair the ligament. Now, however, we transect the ligament with a z-shaped cut; this method allows us to repair the ligament without using any cadaver tissue.

In other modifications to the traditional approach, we wrap a piece of NeuraGen Nerve Guide (Integra Life-Sciences, Plainsboro, N.J.), a nerve-protecting sheath made of collagen, around the nerve to prevent the formation or reformation of scar tissue. To promote nerve healing, we then cover the nerve with platelet-rich plasma that has been prepared from the patient's own blood. The plasma contains growth factors that stimulate the production of myelin-producing cells. Before closure, we also place a pain pump catheter along the course of the nerve. We believe that infusion of bupivacaine for 10-20 days postoperatively decreases the risk of central sensitization to pain and allows patients to be more mobile after surgery, which we encourage. It also may reduce the risk of scar formation. When neuropathic central pain is believed to be a significant problem, as it often is in patients whose nerves have been injured by surgical mesh, we also administer ketamine. An infusion of this old anesthetic can erase or reverse the troubling phenomena of central sensitization to pain. Nerve entrapment involving mesh requires lengthy surgery. While other surgeons may trim the mesh, I firmly believe in removing all the mesh because we cannot determine which part of the mesh is causing pain.

Outcomes data from France show that approximately 30%-40% of patients are pain free after surgical decompression, with another 30% reporting improvement in pain and 30% reporting no change in their pain levels (Eur. Urol. 2005;47:403-8).

At our institution, using national scientific standards for the reporting of pain and extent of pain improvement, we have found that 70% of patients who undergo transgluteal surgical decompression have at least a 20% improvement in pain. Within this category are a significant number of patients who are pain free, and many who report improvements of 50% or more.

Interestingly, we have found that outcomes are similar among our much smaller number of "re-do" surgical patients. Thus far we have performed approximately 20 such transgluteal procedures - 17 on patients who had re-scarring of the nerve after surgery performed at other institutions, and 3 who had surgery many years ago in our practice, before we were able to optimally visualize the entire nerve and before we made modifications to improve the procedure. Just as with our first-time surgeries, approximately 70% of patients who underwent a second procedure had at least a 20% improvement in pain.

In all cases, the pudendal nerve recovers slowly, especially when it has been en trapped and injured for a long time, and improvements in pain often do not occur until about 4 months after surgery. Improvement typically continues for some time, up to 18 months after surgery. Patients may still have pain related to muscle spasms after surgery, so continued physical therapy and/or more Botox injections are often beneficial. Patients must also, of course, continue to avoid any offending factors or activities.

VIEW VIDEO ONLINE

* To view a video on surgery to treat pudendal neuralgia by Dr. Hibner, scan this QR code or visit SurgeryU at www.aagl.org/obgynnews

Dr. Hibner said he has no relevant financial disclosures.
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Title Annotation:GYNECOLOGY
Author:Hibner, Michael
Publication:OB GYN News
Date:Mar 1, 2012
Words:2622
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