Pudendal Nerve Entrapment Syndrome

History

The presenting features of PNE are discussed below[4]

1. It causes pain, numbness, and dysfunction in the distribution of the pudendal nerve that includes genitalia, rectum, and terminal urinary tract.
2. Sexual dysfunction, including persistent arousal, dyspareunia, vulvodynia, and male impotence.[14]
3. Sphincter dysfunction presenting as dyschezia, fecal incontinence, and urinary hesitancy.[15]
4. Foreign body sensation in the anus, rectum, urethra, or vagina.

Physical Examination

The physical examination in patients with PNE is relatively normal, except for pain reproduction.[16] The symptoms depend on the site of entrapment. If the nerve gets entrapped at the ischial spine or the sacrospinous ligament, it causes pain medial to the ischium. Similarly, tenderness over the greater sciatic notch results when the nerve gets entrapped at, the greater sciatic notch. Entrapment at the piriformis leads to spasm and tenderness of piriformis muscle. Lastly, entrapment at the Alcock canal and obturator internus result in tenderness and spasm of the obturator internus muscle.

In some cases, a transrectal or transvaginal examination might be included in the patient examination to exclude intrapelvic entrapment.

Pudendal nerve entrapment is a potentially challenging condition to diagnose because there are no specific diagnostic tests. The clinician needs to realize that it is exceedingly mandatory to get a thorough history and perform a detailed physical examination to reach a diagnosis.[17] Dr. Roger Robert published the Nantes criteria to diagnose PNE and appears in detail below. This criterion has validation by many European physicians who have ample experience treating similar conditions.

Nantes Criteria[17]

Inclusion criteria:

1. Pain co-relates with the anatomical distribution of pudendal nerve: Pudendal nerve supplies external genitalia. The pain can be superficial or deep in the vulvovaginal, anorectal, and distal urethra.
2. Pain predominantly in sitting position: This symptom favors nerve compression because if there is a decrease in mobility of the nerve, it makes the nerves vulnerable to compression against hard ligamentous structures. This aspect of pain is dynamic as the pain results from compression and not by sitting position. 
3. The patient does not get up with pain at night, although many patients may experience difficulty going to sleep because of pain.
4. There is no sensory loss: The presence of superficial perineal sensory impairment indicates a sacral root-lesion rather than PNE.
5. Relief of pain with pudendal nerve block: This essential criterion is not specific as any perineal disease other than entrapment can cause pain in the anatomic region of the pudendal nerve. A negative block also doesn’t exclude the diagnosis if there is a lack of precision or when performed too distally.

Complementary diagnostic criteria:

1. Pain is of a burning, shooting, or stabbing nature and associated with numbness.
2. Allodynia or hyperpathia
3. Foreign body sensation or heaviness in rectum or vagina.
4. The pain progressively increases and peaks in the evening and stops when the patient sleeps.
5. Pain is more on one side.
6. Pain is more prominent posteriorly and is triggered minutes or hours after defecation.
7. Tenderness that is felt around the ischial spine during a digital vaginal or rectal examination.
8. An abnormal result on neurophysiological tests

Exclusion criteria:

1. Pain exclusively in the territory not served by the pudendal nerve. It can be in the hypogastrium, coccyx, pubis, or gluteus.
2. Pain is associated with pruritus (more suggestive of a skin lesion).
3. Pain entirely paroxysmal in nature.
4. An imaging abnormality can justify the cause of the pain.

Associated signs:

1. Pain in the buttock 
2. Referred sciatic pain
3. Pain in the medial thigh (indicates obturator nerve)
4. Pain in the suprapubic region
5. Increased frequency of urine or pain with a full bladder
6. Pain after ejaculation
7. Pain worsens hours after sexual intercourse. 
8. Erectile dysfunction
9. A normal result on electrophysiological tests

Diagnostic Tests

The following tests can help in the diagnosis:

1. Diagnostic blocks: In females, the unguided block can be performed vaginally and in males transperineally. If there is pain relief following the procedure, it indicates that pudendal nerve pathology is the likely cause of pain. The absence of pain relief doesn't necessarily mean that the patient doesn’t have the condition as it can be because of operative error as well. Image-guided blocks (use of fluoroscopy, ultrasound, CT scan ) increases the efficiency of performance.[18]
2. Quantitative sensory threshold testing works on the principle that compressed nerves cannot detect and transmit changes in vibration and temperature sensation. Thus patients with nerve injury are unable to detect gradual temperature changes.[19]
3. High-frequency ultrasonography is helpful in the detection of the site of compression. Compressed nerves appear flat, whereas inflamed nerves appear edematous.[20]
4. Doppler ultrasound has a role in the diagnosis of PNE. As the pudendal nerve and vessels course together in a neurovascular bundle, the assumption can be if there is nerve compression, it would also cause vein compression as well, which is diagnosable with a doppler ultrasound.[20]
5. MRI (magnetic resonance imaging) can help in ruling out other causes of chronic pain. The advancement of MRI techniques in evaluating peripheral nerves provides a detailed description of the anatomy, fascicular details, the blood supply of nerve, and 3-D anatomy.[21] It also helps in localizing the site of entrapment.
   Functional MRI assesses nerve integrity based on their biological properties. Currently, it is considered experimental and inconclusive.[22]

There are no specific and consistent radiological findings in patients with PNE, and further research is necessary.

If the patient fulfills the Nantes criteria, no further investigation is needed to make the diagnosis. However, if the patient lacks any of the criteria, further evaluation should be pursued. MRI helps to rule out other causes of chronic pain in such cases.

The treatment options are as below:

1. Conservative: Avoidance of painful stimulus is one of the most important parts of the treatment. For instance, if cycling causes pain, the patient should use proper padding or cease the activity. Similarly, patients who present with pain on prolonged sitting should adopt lifestyle modifications to minimize sitting.
2. Physical therapy: Pelvic floor physical therapy works best for patients in whom pain results from muscle spasms. Physical therapy helps in the relaxation of pelvic floor muscles by releasing spasm and muscle lengthening. 
3. Pharmacologic therapy: The drugs used are analgesics, muscle relaxants, and anticonvulsants (including gabapentin and pregabalin). There are no randomized trials to study and evaluate the efficacy of these drugs.
4. Pudendal nerve block: The other treatment modality is infiltration with a local anesthetic or steroid in an area encircling the pudendal nerve. The block can be given unguided or with the aid of ultrasonography, fluoroscopy, or computed tomography (CT) scan. The most consistent technique is with the use of a CT scan.[23]
5. Surgical decompression is considered the best treatment for PNE. The four different approaches are transperineal, transgluteal, transischiorectal, and laparoscopy.[24] All methods destroy nerve fibers. It helps in removing the cause of the compression. Erdogru described a new technique (Istanbul technique) of laparoscopy using the omental flap in 27 patients. The outcome measurement was in terms of pain scores and quality of life. Approximately 81% of patients had more than 80% reduction in pain after six months. Laparoscopy has the advantage of a better surgical field, but it has a learning curve.[24]
6. Neuromodulation: This latest treatment includes using a peripheral nerve stimulator, which causes stimulation of the pudendal nerve in the ischioanal fossa. The first case report of this technique by Valovska mentioned the successful management of a patient with pudendal neuralgia with minimally invasive transforaminal sacral neurostimulation.[25] A prospective trial of 27 patients with refractory pudendal neuralgia showed promising results with the use of stimulation of conus medullaris, in which twenty out of 27 patients responded, and out of those twenty patients, all had long term relief.[26]
7. Pulsed radiofrequency: Pulsed radiofrequency is a relatively new neuromodulation technique and is considered safer than continuous radiofrequency ablation. Current literature suggests that it involves the use of electromagnetic radiation to cause neuromodulation. It is useful for chronic refractory neuropathic pudendal neuralgia.[27]
8. Lipofilling: This is a relatively new technique for the treatment of pudendal neuralgia. Venturi described this technique in fifteen female patients. It requires an autologous injection of adipose tissue along with stem cells in the pudendal canal. The results of ten patients showed decreased pain and a better quality of life at the end of six months.[28] Since this study was of small sample size, and there was no control group, further research in this area is necessary for a more comprehensive application.

Since there is no confirmatory diagnostic test, pudendal neuralgia is a diagnosis of exclusion. Other conditions merit consideration before making a final diagnosis.[29]

1. Compression by an external source including a tumor or metastasis
2. Superficial infections of the skin in the dermatomes covered by the pudendal nerve
3. Neuropathy of the sacral region is caused by damage to the sacral nerve plexus.
4. Childbirth that causes a stretch of the perineum
5. Complex regional pain syndrome, a chronic pain condition that causes pain in one of the limbs and usually occurs after an injury.

Pudendal neuralgia due to PNE affects the quality of life immensely. However, it does not affect life expectancy.

The complications associated with pudendal nerve block are[30]:

1. Laceration of the vaginal mucosa
2. Accidental intravascular injection of a local anesthetic can cause cardiovascular and CNS toxicity. The patient can present with palpitations, hypotension, bradycardia, dysarthria, tinnitus, drowsiness, confusion, loss of consciousness, and convulsions.
3. Hematoma from injury to the pudendal artery
4. Infection

Patients should be educated to avoid painful stimuli and actively participate in physiotherapy. Lifestyle modifications are one of the essential elements of the treatment plan.

It is crucial to understand that all types of pudendal neuralgias are not the result of PNE in the treatment planning of patients with chronic pain. It is essential to realize that the pudendal nerve can get trapped at different locations, and therefore, all patients will not benefit from the same therapy. Patients with chronic pain syndromes tend to get frustrated with multiple failed treatments and can be clinically depressed as well.[31]

A study was conducted by Raynor et al. on 1024 patients to study the prevalence of depression in patients with chronic pain and its impact on health care cost. They categorized 60.8% of patients with chronic pain into probable depression and 33.8% into severe depression based on a questionnaire survey. They also reported higher health care cost amongst patients with depression (p=0.001).[32] Similar results can be seen in data analysis by the medical expenditure panel survey of 26671 patients from 2008 to 2011. The research found that different levels of pain interference increase the total health care cost.[33]

Chronic pain poses a mental and economic burden on the patient. These aspects should be considered when providing care to patients.

Pudendal neuralgia due to PNE is a rare neuropathic condition. It causes a significant impairment of quality of life. It often does not get diagnosed promptly, and most patients get treated for other conditions. Thus Nantes diagnostic criteria were established and validated by an interprofessional team to aid in the diagnosis and further treatment of such patients. If the patient fulfills the Nantes criteria, no further investigation is required. However, if any of the criteria are not present, the patient should be further evaluated, and MRI is generally done to rule out other causes of chronic pain. Individualized treatment is necessary. It typically requires permanent lifestyle changes and physical therapy. The treatment options include pharmacological therapy, CT guided blocks, decompression surgery, and neuromodulation.

A well-coordinated interprofessional healthcare team comprised of a pain physician, surgeon, anesthesiologist, nurse, radiologist, and physiotherapist to help in physical rehabilitation is necessary to treat this challenging neuropathic syndrome. All these disciplines need to collaborate across interprofessional boundaries to optimize care and outcomes. [Level 5]