What investigations can be done to diagnose the syndrome?
 
The sacrum, by virtue of its anatomic location, is a structure that presents itself to the attention of multiple medical specialists. This is why many people with chronic pelvic pain will visit many gynecologists, urologists, imaging specialists, gastroenterologists, neurologists and pain specialists before finding the correct diagnoses.

Pudendal neuralgia is a rare condition, and it is seldom diagnosed correctly in a short period of time. Sadly, many people with pudendal neuralgia (PN), pudendal neuropathy (PN), or pudendal nerve entrapment (PNE) are still searching for answers within the medical system. Many are being misdiagnosed over and over, some even having inappropriate and unnecessary surgeries. Additionally, many are being labeled by doctors who cannot figure out what is wrong with them as "head cases" and are sent off to psychiatrists.

Pudendal nerve entrapment syndrome is mainly a clinical diagnosis based on:
  • History
  • Characteristic symptoms and aggravating or relieving factors
  • Typical location of symptoms.

 
History:

What is your history? Were you exercising heavily, did you have an accident, pelvic surgery, vaginal delivery, or were you sitting long hours? Is your pain in the distribution area innervated by the pudendal nerve? Is there increased pain or tenderness when your doctor presses along the course of the nerve via the rectum or vagina? The most constant element is a replication or worsening of the pain during a rectal/vaginal touch at the ischial spine area. This touch must be done by the end of the finger on the postero-lateral wall of the rectum for men or the side of the vagina for women at the ischial spine and alcock's canal. What is your history? Were you exercising heavily, did you have an accident, pelvic surgery, vaginal delivery, or were you sitting long hours? Is your pain in the distribution area innervated by the pudendal nerve? Is there increased pain or tenderness when your doctor presses along the course of the nerve via the rectum or vagina? The most constant element is a replication or worsening of the pain during a rectal/vaginal touch at the ischial spine area. This touch must be done by the end of the finger on the postero-lateral wall of the rectum for men or the side of the vagina for women at the ischial spine and Alcock's canal.

The so called "skin rolling test" can be a helpful clinical sign. In this test, a thick roll (or fold) of skin just below and lateral to the anus is pinched and then rolled forwards. If pain is elicited, then this suggests the pudendal nerve is compressed (Figure-1).

It is important to exclude lesions in the pelvis which might compress the nerve by an ultrasound or computed tomography scan. Sometimes special nerve studies (electrophysiological studies) can be helpful. Local anaesthetic nerve blocks of the pudendal nerve may be helpful to confirm the diagnosis in some cases if it demonstrates complete abolition of symptoms after a nerve block.

 
Magnetic resonance imaging (MRI)

Often the pudendal nerve expert doctors recommend an MRI to rule out obvious problems such as tumors or spinal abnormalities. MRI's and CT scans cannot see the nerves. But they are important to exclude any other organic lesions or to find other causes of nerve compressions especially at the level of the spine. Many other conditions like cauda equina syndrome and arachnoiditis have some symptoms that mimic PN. One should have at least a CT scan or MRI of the lumbosacral area and lumbosacral plexus. Often with pudendal neuralgia, CT scan and MRI exams will show no irregularities. The PNE doctors each have their own protocol so while it is OK to have these tests locally, before scheduling your MRI it is good to check with the PNE doctor you may eventually wish to see so that you know exactly what type of MRI they require. This can help you avoid having an MRI twince.

Magnetic resonance neurography (MRN) is similar to an MRI but it uses special software to enhance the image of small nerves that are difficult to see on a normal MRI. There are only a handful of centers in the world where you can have this test and entrapments do not always show up so the test is only accurate for a diagnosis of PNE part of the time

 
Electro physiological testing including EMG's and PNMLT

A PNMLT is an electro physiological procedure, similar to an EMG (electromyogram), which measures the speed of nerve conduction. This exam is done by a neurologist. Not all neurologists have the necessary equipment to do this type of examination on the pudendal nerve. During this exam, the pudendal nerve is stimulated electrically inside the rectum (or vagina) at the ischial spine with electrodes on the tip of a special glove. The speed of the nerve conduction is recorded by a small needle inserted in the perineum. If the nerve responds slower than normal, this gives an indication that the nerve may be entrapped or damaged.

The PNMLT examines only the motor function of the nerve. There is no way to test the sensory fibers of the nerve which transmit pain. The reason for the test is based on the assertion that an abnormal motor function will most likely conceal a sensory affection as well but this is not always true. So, an abnormal PNMLT indicates that the pudendal nerve is affected but a normal reading does not rule out PN. In this case a sensory neuropathy could exist even if the motor fiber of the nerve has not been affected yet. This is more common with people who have had PN only for a short period of time

The neurological examination can be completed by the measurement of the anal reflex latency, measurements of the bulbocavernosus reflex latencies (BCRLs), somatosensory evoked potentials of the pudendal nerve (SEPPNs) and the sensory conduction velocity of the dorsal nerve of the penis (SCVDNP). Those exams can give further information about the condition of the nerve or the origin of the pain.

Results of these tests are not 100% accurate for a diagnosis of pudendal neuralgia or PNE but they can help add to the overall picture as to how well the nerve is functioning. Sometimes, although not always, there will be a latency with the EMG and PNMLT testing that indicates a neuropathy. There are some doctors who rely mostly on the PNMLT and there are others who rely mostly on the EMG. Some doctors feel that utilizing the EMG, they can actually "tell" where the entrapment is.

 
Pudendal nerve blocks

A diagnostic block, or a "blockage of the nerve", is an injection with a local anesthetic such as lidocaine or one of its derivatives (also used by dentists). The block is usually done in the buttock to reach the pudendal nerve at the ischial spine where it is most often entrapped between the sacrospinous and sacrotuberous ligaments. One block for each side affected is necessary. If the pain diminishes immediately or even vanishes completely as long as the effect of the local anesthetic persists, this is an indication that your pudendal nerve may be compromised in some fashion, and that possibly some damage to the nerve has occured.

Injections can serve as a diagnostic tool but can also serve as a therapeutic tool. In the latter case, the injection consists of a steroid as well as an anesthetic agent.

If you experience significant pain relief for even a short time (several hours) from a nerve block that may mean you have pudendal neuralgia. However pudendal nerve blocks can temporarily ease the pain caused by other problems in the distribution area of the pudendal nerve so the nerve block is only one of the tools used in the diagnosis of PNE.

In the context of PN, a nerve block involves injecting a liquid at a precise location near a nerve. For a small nerve like the pudendal that takes slightly different paths in different people, this requires more than just studying a person's body and deciding where to insert the needle, at what angle, and how deep. It requires imaging of some type, such as X-ray (fluoroscope), ultrasound, MRI or CT. Without the accuracy these imaging systems provide, it is difficult or impossible to know if the needle tip is located correctly. If incorrectly located, the nerve can be damaged or the injected liquid will be too far away to have its intended effect. Dr. Bensignor says the needle tip must be within one millimeter of the target. However, even with image guidance it is possible for the block to miss its mark.

There are two main types of injected liquids: a local anesthetic and slow-release steroids. The local is a short term diagnostic tool. If the pain goes away and stays gone for the short term, the location was correct and the nerve can be suspected of being a contributor or the sole source of pain. The steroids are a long term therapeutic attempt. In some cases they will cause the nerve, if it is irritated, to get better. This can take days or weeks, and improvement may be temporary or permanent. This delay explains why physicians prefer a delay of several weeks between nerve blocks with steroids. If the nerve is not irritated, the steroids have no effect. Some doctors use heparin, an anti-inflammatory medication, instead of steroids.

Two main locations are used. The ischial spine block is done by injecting into the sacrospinous ligament. Alcock's canal block is done by injecting into the sacrotuberous ligament. These are not the same as the blocks carried out for childbirth pain. In some cases the blocks may worsen the pain a little but this should last only a few weeks. In a few cases nerve blocks have caused a permanent worsening of pain possibly due to the nerve being "nicked" by the needle, a reaction to the medication, or formation of scar tissue.

When the nerve block is conducted under guidance, the patient is asked to lie down in the prone position. Using a small needle the doctor injects an anesthetic to numb the buttocks prior to injecting with the larger needle that targets the pudendal nerve. When the doctor is able to find the pudendal nerve, he will then inject either the local anesthetic and the long term steroid or heparin. The procedure itself lasts approximately 30 minutes. This is done on an outpatient basis. No overnight stay is required.

If the injection relieves your pain that is considered a positive response to the nerve block and the pudendal nerve may be the source of your pain. If the injection did not provide any relief there are two possible conclusions

1. The pain is not as a result of the pudendal nerve or
2. The physician did not get close enough to the pudendal nerve to feel any effects. After a pudendal nerve block it is possible to evaluate whether the block hit the target of the pudendal nerve by testing the perineum, clitoral, and anal areas for loss of sensation and numbness. Sometimes the physician might order another block four to six weeks after your first block, to make sure that they can entirely rule out pudendal neuralgia, by trying to see if they can get close enough to the nerve again.

Occasionally medication from the nerve block can wander into the area of the sciatic nerve making it difficult for the patient to walk. This problem typically subsides within 24 hours.

In-Conclusion
None of the diagnostic tests for PN and PNE are 100% accurate so the more of these tests you have the better your overall picture will be in determining your diagnosis.
The final diagnosis of pudendal neuralgia is based on a person having several or all of these criteria.
  1. Typical PNE symptoms
  2. An abnormal electro physiological test
  3. A positive response to the nerve block
  4. A distinct abnormality on an MRN
  5. Pain elicited upon pressing along the course of the nerve
  6. Elimination of other diseases being the cause