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Diagnostic path.
By Pierre Gauvin , Greg Thibeau - December 2003
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 this type of 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 (also known as “pudendal neuropathy” or “pudendal nerve entrapment”) are still search for answers within the medical system. Many are being misdiagnosed over and over, some even having inappropriate and unnecessary surgeries. Additionally, many are being labelled by doctors who cannot figure out what is wrong with them as “head cases”, and are sent off to psychiatrists.
This page is aimed at giving you a roadmap for a pudendal neuralgia diagnosis. The predominant factor in the diagnoses of pudendal neuralgia are the symptoms.
Then, the medical exams that one should have are:
1. The clinical exam
2. MRI or CT Scan
3. Pudendal Nerve Motor Latency Test (PNMLT)
4. Diagnostic block
1- The clinical exam
The clinical exam is rather poor. The most constant element is a replication or worsening of the pain during a rectal 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. The doctor should also look for the following signs:
The perineum, and genital may have a decreased threshold response to tactile stimuli, but will have a normal threshold response to pain.
Usually the bulbo-cavernous and anal reflex are not affected.
Very often there are other painful areas in the surrounding region (piriformis muscle, tailbone pain...). Most of the time this is a reaction to the nerve pain. But in some cases the piriformis muscle could pinch the nerve and be the main cause.
A clinical exam should be done first to rule out other more conventional conditions such as prostatis, vaginit or urinary infections. If the pain persists after the conventional medication then the next steps in the Diagnosis of pudendal neuralgia can be pursued.
2- Magnetic resonance imaging (MRI) or computerized tomography (CT Scan).
Those devices cannot see the nerves. But they are the best imaging technology available today. So, 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 have some symptoms that mimic PNE. One should pass at least a CT scan or MRI from the S5 disk to S1. In the case of pudendal neuralgia, CT Scan and MRI exams will show no irregularities.
3- Pudendal Nerve Motor Latency Test (PNMLT)
A PNMLT is an electrophysiological 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. 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 for 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. So, an abnormal PNMLT indicates that the pudendal nerve is affected but a normal reading does not rule out PNE. In this case an entrapment could exist even if the motor fiber of the nerve has not been affected yet. This is more common with people who have had PNE only for a short period of time. Nevertheless, the PNMLT is the most accurate neurological examination for the pudendal nerve.
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.
5- Diagnostic block.
A diagnostic block, or a "blockage of the nerve", is an injection with a local analgetic 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 analgetic persists, this is an indication that your pudendal nerve is being compromised in some fashion, and that possibly some damage to the nerve has occurred.
Injections can serve as diagnostic tool but can also serve as a therapeutic tool. In the latter case, the injection consists of steroid. See Treatments for more information.
These injections must be given only under strict radiological control for safety reasons since the exact placement of the needle is critical in confirming the diagnoses, or even curing the patient. Injections at the ischial spine, can be done under fluoroscopy or CT scan while the final injection done into alcock’s canal must be done under CT guidance only. The complete “how to” guide for pudendal nerve injections for radiologist can be found here.
In search for a diagnoses
The final diagnoses of pudendal neuralgia is based on a persona having at least two out of the three criteria:
- typical PNE symptoms,
- an abnormal electrophysiological test
- a positive response to the nerve block.
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