Pudendal Nerve Entrapment

Pudendal nerve entrapment (PNE), also known as Alcock canal syndrome, is an uncommon source of chronic pain, in which the pudendal nerve (located in the pelvis) is entrapped or compressed. Pain is positional and is worsened by sitting. Other symptoms include genital numbness, fecal incontinence and urinary incontinence.

The term pudendal neuralgia (PN) is used interchangeably with "pudendal nerve entrapment", but a 2009 review study found both that "prevalence of PN is unknown and it seems to be a rare event" and that "there is no evidence to support equating the presence of this syndrome with a diagnosis of pudendal nerve entrapment," meaning that it is possible to have all the symptoms of pudendal nerve entrapment (otherwise known as pudendal neuralgia) based on the criteria specified at Nantes in 2006, without having an entrapped pudendal nerve.

A 2015 study of 13 normal female cadavers found that the pudendal nerve was attached or fixed to the sacrospinous ligament in all cadavers studied, suggesting that the diagnosis of pudendal nerve entrapment may be overestimated.

Symptoms

There are no specific clinical signs or complementary test results for this condition. The typical symptoms of PNE or PN are seen, for example, in male competitive cyclists (it is often called "cyclist syndrome"), who can rarely develop recurrent numbness of the penis and scrotum after prolonged cycling, or an altered sensation of ejaculation, with disturbance of micturition (urination) and reduced awareness of defecation. Nerve entrapment syndromes, presenting as genitalia numbness, are amongst the most common bicycling associated urogenital problems.

The pain is typically caused by sitting, relieved by standing, and is absent when recumbent (lying down) or sitting on a toilet seat. If the perineal pain is positional (changes with the patient's position, for example sitting or standing), this suggests a tunnel syndrome. Anesthesiologist John S. McDonald of UCLA reports that sitting pain relieved by standing or sitting on a toilet seat is the most reliable diagnostic parameter.

Other than positional pain and numbness, the main symptoms are fecal incontinence and urinary incontinence.

Differential diagnosis should consider the far commoner conditions chronic prostatitis/chronic pelvic pain syndrome and interstitial cystitis.

Causes

PNE can be caused by pregnancy, scarring due to surgery, accidents and surgical mishaps. Anatomic abnormalities can result in PNE due to the pudendal nerve being fused to different parts of the anatomy, or trapped between the sacrotuberous and sacrospinalis ligaments. Heavy and prolonged bicycling, especially if an inappropriately shaped or incorrectly positioned bicycle seat is used, may eventually thicken the sacrotuberous and/or sacrospinous ligaments and trap the nerve between them, resulting in PNE.

Diagnosis

Similar to a tinel sign digital palpitation of the ischial spine may produce pain. In contrast, patients may report temporary relief with a diagnostic pudendal nerve block (see Injections), typically infiltrated near the ischial spine.

Electromyography can be used to measure motor latency along the pudendal nerve. A greater than normal conduction delay can indicate entrapment of the nerve.

Imaging studies using MR neurography may be useful. In patients with unilateral pudendal entrapment in the Alcock's canal, it is typical to see asymmetric swelling and hyperintensity affecting the pudendal neurovascular bundle.

Treatment

Treatments include behavioral modifications, physical therapy, analgesics and other medications, pudendal nerve block, and surgical nerve decompression. A newer form of treatment is pulsed radiofrequency.

Physical therapy

There are stretches and exercises which have provided reduced levels of pain for some people. There are different sources of pain for people since there are so many ligament, muscles and nerves in the area. Sometimes women do pelvic floor exercises for compression after childbirth. However, there have been cases where the wrong stretches make the constant pain worse. Some people need to strengthen the muscles, others should stretch, while for some people it is purely neurological. There have been cases where doing stretches have helped bicyclists.

Medications

There are numerous pharmaceutical treatments for neuropathic pain associated with pudendal neuralgia. Drugs used include anti-epileptics (like gabapentin), antidepressants (like amitriptyline), and palmitoylethanolamide.

Injections

Alcock canal infiltration with corticosteroids is a minimally invasive technique which allows for pain relief and could be tried when physical therapy has failed and before surgery. A long-acting local anesthetic (bupivacaine hydrochloride) and a corticosteroid (e.g. methylprednisolone) are injected to provide immediate pudendal anesthesia. The injections may also bring a long-term response because the anti-inflammatory effects of the steroid and steroid-induced fat necrosis can reduce inflammation in the region around the nerve and decrease pressure on the nerve itself. This treatment may be effective in 65–73% of patients.

Pulsed radiofrequency

Pulsed radiofrequency has been successful in treating a refractory case of PNE.

Ergonomics

Various ergonomic devices can be used to allow an individual to sit while helping to take pressure off of the nerve. With bicycles the seat height and tilt can be adjusted to help alleviate compression. There are also bicycle seats designed to prevent pudendal nerve compression, these seats usually have a narrow channel in the middle of them. For sitting on hard surfaces, a cushion or coccyx cushion can be used to take pressure off the nerves.

Surgical

Decompression surgery is a "last resort", according to surgeons who perform the operation. The surgery is performed by a small number of surgeons in a limited number of countries. The validity of decompression surgery as a treatment and the existence of entrapment as a cause of pelvic pain are highly controversial. While a few doctors will prescribe decompression surgery, most will not. Notably, in February 2003 the European Association of Urology in its Guidelines on Pelvic Pain said that expert centers in Europe have found no cases of PNE and that surgical success is rare:

Pudendal nerve neuropathy is likely to be a probable diagnosis if the pain is unilateral, has a burning quality and is exacerbated by unilateral rectal palpation of the ischial spine, with delayed pudendal motor latency on that side only. However, such cases account for only a small proportion of all those presenting with perineal pain. Proof of diagnosis rests on pain relief following decompression of the nerve in Alcock’s canal and is rarely achieved. The value of the clinical neurophysiological investigations is debatable; some centres in Europe claim that the investigations have great sensitivity, while other centres, which also have a specialized interest in pelvic floor neurophysiology, have not identified any cases.

— European Association of Urology, Guidelines on Chronic Pelvic Pain

Three types of surgery have been done to decompress the pudendal nerve: transperineal, transgluteal, and transichiorectal. A follow-up of patients of this surgery after 4 years found that 50% felt their pain had improved to various extents, although control patients were not followed up for comparison. If surgery does bring relief of symptoms, patients will mostly experience it within 4 weeks of surgery.

However, the studies and surgical methods cited above generally focused on the Alcock’s canal and the area between the sacrotuberous and sacrospinous ligaments as likely sites for entrapment. More recent studies have identified possible entrapment sites anterior to Alcock’s canal.