Part III of our “Demystifying Pudendal Neuralgia” Series
How does PNE (pudendal nerve entrapment) occur? How is it diagnosed? When is a patient a good candidate for the pudendal nerve decompression surgery? When are they not?
These are among the questions we asked two of the leading experts on the controversial diagnosis PNE and the decompression surgery associated with it: Michael Hibner, M.D., a gynecologic surgeon at St. Joseph’s Hospital and Medical Center in Phoenix, Ariz. and Mark Conway, M.D., a gynecologic surgeon at St. Joseph’s Hospital in Nashua, New Hampshire. (See full bios below.)
Q: How does PNE occur?
In my experience it is usually a traumatic event. In my practice, the majority of women with PNE have had some kind of gynecological surgery, such as some kind of mesh procedure. Another cause for women can be childbirth. The nerve runs on the inside of the bony pelvis and as the baby’s head comes out it may crush the nerve, which is a mechanical compression. There is also the possibility of the nerve being stretched during childbirth, which is a tension injury. Another possible mechanism PNE can occur is the result of vigorous exercise, such as lower extremity exercises, the so-called “dead weight lift,” and bicycling.
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.
It can occur from a variety of different mechanisms. I tell my patients: There are lots of roads that lead to Rome. Many patients I deal with have a direct or an indirect surgical injury to the nerve such as a surgery to correct prolapse, especially when there is a use of prosthetic mesh to correct the prolapse. Oftentimes those mesh materials are put in close proximity to the pudendal nerve, and can cause injury that way.
Other mechanisms include trauma to the area from a car accident for example where the pelvis fractures or whiplash type of phenomenon occurs. Also, taking a direct fall to the buttock area can cause scar tissue to form from some degree of hematoma formation, which would cause some degree of bleeding back into the area where the nerve runs between two ligaments, so that can lead to scar formation that can trap the nerve or irritates the nerve.
Still another mechanism is obstetrical trauma. There are different ways for this to occur. One way is for there to be bleeding into the nerve space, and then as the blood clot resolves it leaves fibrosis and the nerve is compressed that way. Lifestyle can also play a role such as if a patient is an avid cyclist.
Another thing to consider is there is probably also some sort of anatomic predisposition in some patients, meaning the space between the two ligaments that the nerve traverses is more narrow in some patients, which will set them up to get the condition. Another thing that we often see in surgery is that the nerve trunk itself actually perforates these ligaments meaning it actually goes through the ligaments rather than between them. Therefore, they are kind of born with a low level of entrapment that is then very easily triggered later in life, sometimes by very innocuous activity.
It is extremely plausible that surgical insult can entrap a nerve. Red flags go up when patients tell me they had no prior symptoms of pelvic pain and then woke up in the operating room with signs of pudendal neuralgia. I immediately refer these patients to consult with Drs. Conway and Hibner.
Q: How is PNE Diagnosed?
There is no way to definitively diagnose PNE. It is a diagnosis of exclusion.
The history is extremely important. First off, the patient has to have had a traumatic event or “events” because a series of micro traumas can lead to entrapment. Riding a horse for instance is an example of one micro trauma. One does not just wake up one morning and have PN (unless there was the above-mentioned surgical insult).
In our practice we have a system to determine what is causing a patient’s symptoms and whether the pudendal nerve decompression surgery is a treatment option.
First, when a new patient calls we schedule them for several things. They all get a pelvic MRI. It’s a 3-Tesla MRI that is focused on the pudendal nerve, therefore, we perform this even if they have had an MRI elsewhere. The second step is a one-hour physical therapy evaluation with our pelvic floor physical therapist. This includes a history and an physical examination. This is done to identify musculoskeletal issues as pain generators. Once I have the MRI I evaluate the patient. Based on their history, PT evaluation and MRI results we come up with a plan.
What I generally do with most of the patients is start with Botox injections into the pelvic floor because almost all patients with PN or presumed PNE have pelvic floor muscle spasms. You want to eliminate that muscle spasm first before you do anything else. The patient undergoes Botox injections, which takes about two weeks to start working. If the patient continues to have pain after the Botox then our PT re-examines them to determine whether the muscles have relaxed or not. If the muscle have not relaxed we take into consideration whether we injected enough Botox or if we injected the right spot and repeat if necessary. We see about 80 percent of our patients improve after Botox, and it they do improve, it’s a significant improvement. Botox typically has an “all or none” effect. It either works well or doesn’t work at all.
However, if the muscles have relaxed and they are still in pain then we do what is known as CT guided pudendal nerve blocks. (These nerve blocks can also give us information about where there is compression if we suspect compression. This allows us to decide which surgical approach to use.) If they don’t work then we start talking about possibly doing the decompression surgery. In the meantime, patients are doing PT.
I should point out that I very rarely operate on anyone who improves as a result of our protocols, even if it’s only a small improvement.
I think the etiology is the strongest diagnostic indicator. Because there are no tests to diagnose entrapment, a team approach with a thorough assessment is absolutely crucial.
The most important components to the workup and diagnosis of PN are the history and physical exam. In short patient’s complain of pain in the distribution of the pudendal nerve increased with sitting. The pain can be a burning sensation, lancinating, electrical zapping, or aching. The pain is usually not as bad in the morning, and is at least somewhat relieved sitting on a toilet seat. The patients may have a variety of other symptoms including urinary, defecatory, and sexual dysfunction. They often have a clear mechanism leading to the condition(i.e. antecedent surgery, sporting activity etc.). On exam they may have allodynia, skin rolling sensitivity, pelvic floor hypertonus and tenderness.
Most importantly compression of the nerve on rectal exam between the SSL and STL will cause pain and flare up the patient’s PN symptoms even after the exam is over.
Can you tell us about your diagnostic workup for PNE?
Our diagnostic work up varies to some degree on the patient. We offer nearly all our patients a pudendal nerve EMG. This is a highly specialized test devised by Eric de Bisschop, MD, a neurologist in France. It measures a series of sacral reflexes, and is helpful to confirm nerve dysfunction.
It’s use to localize the possible site of nerve irritation, or quantify the degree of nerve dysfunction is less clear. We have no large database of published reports on the utility of the test, but in our quite substantial clinical experience it correlates well with patient complaints and operative findings.
Imaging such as MRN or 3T MRI is also available with limited data on its usefulness. I order these tests on select cases where the standard evaluation is not clear and further data is needed.
PT evaluation is also essential to evaluate the myofascial component of the pain and to look for other possible pathology such as hip pathology. Of course other studies such as lumbar MRI, hip MR arthrogram etc. are used as indicated to look for other causative or associated pathology. In addition, evaluation for autoimmune disease or Lyme disease may be indicated in some patients.
Also in some patients selective diagnostic nerve blocks (i.e. pudendal, ilioinguinal, PFCN, or obturator) are used to further elucidate which nerves are affected. In some patients they will have a totally effective PN block with numbness in the nerve distribution, but no pain relief. This would help exclude PN/PNE as a diagnosis.
Lastly, we do not use Botox as standard therapy but on select cases where severe pelvic floor hypertonus not responsive to PT is a possible cause of the pain.
Q: Can entrapment be seen at the time of surgery?
The answer is yes it can. However, it’s important to keep in mind that we can’t always go by what we see as actually a measure of the patient’s function. At this point we have no studies over time that actually get a correlation of patients’ preoperative, surgical, and postoperative findings.
Q: How can you tell if a patient has PN or PNE?
Again, there is no definitive way of telling.
However, the pudendal nerve motor terminal latency test was used in the past. This test measures the conduction velocity of electrical impulses. This test is not dependable because there is a high rate of both observer variability (two different providers can get two different reads) and variations among patients who have had previous vaginal deliveries or pelvic surgery. A second test, the sensory threshold test, also has questionable reliability. This is test is done by placing varying temperatures on a patient’s skin in the different territories of each nerve branch. The tester asks the patient to report what they feel. If there is a sensation other than heat it is considered ‘positive’.
The biggest issue with these tests is that if a patient has pelvic floor muscle spasm and it is putting pressure on the nerve, he or she will get an abnormal reading. As I already mentioned, most patients with PN have muscle dysfunction therefore we cannot use these tests to confirm PNE. These tests over-diagnoses patients.
Magnetic resonance neurography (MRN) is another test that is used by some physicians. This is another type of MRI. I view this test as very questionable. I have discussed it with my neurosurgery colleagues we all agree. When patients bring me these test results they do not factor into my calculation in any way.
Lastly, there is the three tesla MRI, which I mentioned above. The radiologist who is really known for administering this test is Hollis Potter in New York City. We do a similar test here at St. Joseph’s. And the bottom line is that with this MRI you can not really see the pudendal nerve. Due to the resolution of the test, the MRI pixels on the screen are larger than the actual nerve.
Having said that, we do have our patients get this MRI because there is some information you can get from it. The thinking is that the pudendal nerve runs together with the pudendal vein. Indeed, they’re really attached to each other. So if the pudendal nerve is compressed the pudendal vein is going to be compressed and if you compress the vein, there is varicosity that you can see on the MRI. Again, this is not a direct view of the nerve compression; it’s more of an indirect view showing that the vein is enlarged.
Therefore, the MRI as important. For example, I saw a young patient in her late 20s, who for many years was treated by a top vulvodynia doctor with ointments. When she came to see us she had the MRI done, and on the MRI we saw that she had a tumor in her pelvis that was pressing directly on her pudendal nerve. It was a benign tumor that needed to be removed. The point is that MRIs can provide useful information.
One last thought on using an MRI to diagnose PNE: I think honestly if you want to use an MRI to diagnose PNE then you first have to have a clear understanding of what “normal” is. If one is going to make strong statements that there is nerve compression than we have to show what the normal picture is. Likely, there are people walking around with what we would classify as entrapment that are asymptomatic. With that said, MRIs cannot confirm PNE and patients need to be aware of this.
At the end of the day, no one can say with 100 percent certainty that the nerve is compressed. I look at it like a jigsaw puzzle that we put together using the patient’s history, symptoms, the exam, and then trying to allow for all the other things that could cause pudendal neuralgia. That’s how I make the diagnosis. It is very unlikely that the diagnosis can be made in one visit. The only time I make a diagnosis in the first visit is with the patients who had a surgery and wake up in the hospital with severe pudendal nerve-type pain. In this case, I assume that the nerve has been impinged inside the mesh directly.
How would you diagnose PNE prior to operating on somebody? The fact is you can’t. The imaging techniques available haven’t been proven in any kind of large controlled trial as to how accurate they are and how well they correlate with any surgical findings. We certainly still use those techniques to try to get a better idea of the nerves condition sometimes they are very helpful, but other times they serve up a lot red herrings as far as what the nerve’s condition is. In addition, the pudendal nerve motor terminal latency test can be used, but there isn’t a lot of data on how accurate it is in predicting outcomes on surgeries.
What I always say to patients is that we need to look at how they respond to treatment and start with the least invasive things and then move up from there. We should almost nerve jump to surgery. However, there are a couple of instances that might be exceptions to that rule. For example, there have been patients who have a history of either mechanical trauma or vehicle accident or pelvic fracture etc. or surgical injury where people say” I have never had these symptoms at all prior to surgery or “so this event happened and it’s a major event and ever since then I’ve had the pain”.
And not just the pain, but the patients also actually have end organ dysfunction, such as incontinence or they have numbness. Those patients might be better served to move more quickly to have the nerve operated on because the worry is the longer you leave it at that level of dysfunction, it will just get worse and worse and may be unrecoverable. So that’s the one time where I will be up front about surgery. But that’s about five percent of cases I don’t have an exact number but it’s pretty unusual for me to have that conversation.
I think we are all on the same page here. The team approach is crucial to attempt to differentiate between myofascial causes of PN and entrapment causes of PN. A patient’s response to various therapies can also help us determine the sources of pain. If a patient responds to pelvic floor physical therapy or Botox it is likely myofascial and not entrapment. It seems unlikely that PT would be able to decrease symptoms in cases of actual entrapment.
Q: If you make the decision that the patient’s symptoms are being caused by an entrapped nerve than is surgery the only option?
If we conclude that there is PNE, first off, PT is not going to help. In surgery I can see scar tissue around the nerve and there is no physical therapy technique that will free up that nerve from the scar tissue.
PT is the key treatment for PN but not for PNE.
My primary concern is that we have no way to determine if non-surgically induced PN is caused by entrapment. I do agree that if entrapment is confirmed, which really is based on history, surgery is warranted.
I take a very practical approach with patients, except in the (post-surgical) situations mentioned above. I tell patients to start with the pelvic floor with physical therapy, potentially using nerve blocks as well to reduce nerve irritation, medication to reduce nerve hypersensitivity instructing them to avoid the activities which exacerbate their pain, which primarily involves trying to limit sitting and also other physical activities that increase their pain. And if the patients respond that’s great; I’m not saying they don’t have nerve entrapment, I’m saying the nerve entrapment they have can be treated conservatively.
What other treatments are you using for PNE?
We are using ketamine to treat patients with suspected PNE. We IV- infuse the ketamine, which is an old school anesthesia that isn’t used anymore due to its propensity to cause hallucinations. When it is infused in a dose lower than the hallucination inducing dose, and it’s infused for more than a week in the hospital, it can somehow reprogram the nervous system giving patients a different perception of pain. The great majority of patients experience improvement in their symptoms.
However, it’s a lifelong thing and must be repeated once or twice a month in the office for four hours or so. In addition, these treatments are experimental and are not covered by insurance. They can cost patients thousands of dollars. In addition, ketamine works after surgery. To go this route, I will administer a ketamine infusion during the surgical procedure and then continue it in the hospital afterward while the patient is in recovery. We can also do a five-day in-hospital infusion; however, it is not always covered by insurance. This is our latest protocol, and it more effective than surgery alone.
In addition to the surgery and the ketamine infusion, we also administer Botox. We’re really trying to hit the pain on every front. With the surgery we are decompressing the nerve, with Botox we relax the muscles, and with ketamine we are reprogramming the spinal cord or the central nervous system.
When is surgery NOT the best course of action?
The patients that we feel the least good about surgery have had the condition come out of nowhere, and it’s hard to figure out why a patient would have a problem in this area. Also, we are concerned when nerve blocks don’t help at all. The patient feels the numbness, but continues to feel pain. Typically, if patients have a good response to a block, better chance of having a better outcome. In addition, patients who have pain on both sides may not have a good outcome.
Lastly, studies show that elderly patients and patients who have had their symptoms for a long time have less of a chance of a good outcome.
Check back for Part 2 of our Q&A with Drs. Hibner and Conway where they’ll discuss the pudendal nerve decompression surgery, the risks of the surgery, and when it can be considered a success/failure, among other things.
If you have any questions or comments for Drs. Hibner and Conway, please leave them in the comment section or email to: blog@pelvic
Dr. Hibner is director of the Arizona Center for Chronic Pelvic Pain, St. Joseph’s Hospital and Medical Center, Phoenix. He is a former fellow in advanced gynecologic surgery at Mayo Clinic, Scottsdale, Ariz., and is now professor of obstetrics and gynecology, Creighton University, Omaha, Neb., and associate clinical professor of obstetrics and gynecology, University of Arizona, Tucson.
Dr. Mark Conway is the head of the obstetrics and gynecology department at St. Joseph’s Hospital in Nashua, New Hampshire. Dr. Conway, a Fellow of The American Congress of Obstetricians and Gynecologists, heads a comprehensive pudendal neuralgia treatment center offering conservative therapies, medication management, a surgical solution to treat pudendal nerve entrapment as well as comprehensive post-operative care.