Pudendal nerve entrapment syndrome (ORPHA:60039)
A rare, acquired peripheral neuropathy characterized by chronic neuropathic pain involving the sensory territory of the pudendal nerve (from clitoris to anus or from penis to anus) aggravated by sitting. It is often associated with pelvic dysfunction.
Epidemiology
The prevalence of Pudendal neuralgia (PN) is unknown. A female predominance is reported, with a female/male ratio of 6:4.
Clinical description
PN usually presents between the ages of 50-70 years. and manifests with neuropathic pain of varying intensity in the perineal region. The pain is described as an intense, sharp, burning sensation, and sometimes as numbness. Rectal or vaginal foreign body sensations (sympathalgia) are commonly reported. Pain is unilateral or often medial, and is more intense during the day, when sitting or when wearing tight clothing. The pain is often associated with pelvic sensitization, which explains the urinary (pollakiuria, dysuria), anorectal (dyschezia, increased pain after bowl movement) and sexual (dyspareunia, intolerance of vulval contact, post-coital exacerbation of pain, persistent genital arousal, erectile dysfunction) problems as well as myofascial pain in the buttocks. The co-occurrence of truncal sciatica is common. Several forms of PN exist: benign, regressive, evolutive with flares, stable, and very debilitating forms with progressive symptom aggravation.
Etiology
The pudendal nerve can be compressed or entrapped by posterior pelvis ligaments (comprised of the sacrotuberous and sacrospinalis ligaments), or in the Alcock's canal (due to splitting of the obturator muscle aponeurosis). There is also the possibility of proximal entrapment at the level of the sub-piriformis canal and distal entrapment of the dorsal nerve of the clitoris/penis at the level of the sub-pubic canal. Other causes of pudendal neuralgia may include birth-related difficulties (due to excessive stretching), trauma, surgical, radiation sequalae, intense bicycling, spinal deviation, pelvic skeletal fractures or a tumor. In these cases, the pain is likely to be permanent and sitting position has little or no effect on it.
Diagnostic methods
The diagnostic criteria (Nantes criteria) for PN includes the presence of pain in the distribution of the pudendal nerve that is worsened by sitting, with no objective sensory impairment, which does not provoke awakening in the night, and that is relieved with anesthesia by pudendal nerve block. The diagnosis is strictly clinical and no additional examination can validate the diagnosis with certainty. Imaging tests may be necessary to rule out other diagnoses (pelvic and lumbosacral MRI, endoscopy, infection check-up, etc.). Normal imaging findings do not exclude a diagnosis of PN.
Differential diagnosis
Differential diagnoses include neuropathies of the neighboring nerves (ilio-inguinal, genitofemoral, lower cluneal), coccygodynia (given the location of pain projecting into the anus and rectum, aggravated by sitting position) and myofascial syndromes of the deep gluteus muscles (piriformes, obturator internus muscle, levator ani). Dermatological inflammatory pathologies (psoriasis, vulvar sclerotrophic lichen) should be systematically eliminated. When the pain is not triggered by sitting position, but rather by sexual intercourse, vestibulodynia should be considered. Isolated chronic urethralgia or bladder pain syndrome may be considered when perineal pain varies with urination.
Management and treatment
Management includes the treatment of neuropathic pain with antidepressant therapy (amitriptyline at low dose or duloxetine) or antiepileptic (pregabalin, gabapentin) and percutaneous posterior tibial nerve stimulation. Physiotherapy, osteopathy and short-term psychotherapy are also proposed as first-line solutions. The effect of anesthetic infiltration of the pudendal nerve is limited and its therapeutic effects in the medium and long term have not been demonstrated. In refractory forms, surgical decompression of the pudendal nerve has been effective (the trans-gluteal pathway being the only surgery whose efficacy has been proved). In those where surgery has been ineffective, an implanted neurostimulator can be proposed at the conus medullaris level or on sacral roots and pudendal nerve level.
Prognosis
PN greatly affects quality of life, but has no effect on life expectancy.

                            Last update: 
                            April 2020


                            - Expert reviewer(s): 
                            Dr Amélie LEVESQUE