Pudendal Peripheral Nerve Stimulation For Chronic Pelvic Pain

Introduction

Pudendal neuralgia (PN) is a painful condition resulting from inflammation, compression, or entrapment of the pudendal nerve. PN is one of the most disabling forms of genital pain, affecting approximately 4% of patients complaining of chronic pain. It has devastating effects on a patient’s quality of life, with serious limitations to their usual activities of daily living, particularly if sitting is involved. This is a very common scenario in current society, where many people have sedentary jobs, and commutes are frequent and long. PN can also be associated with depression, anxiety, inability to maintain a sexual relationship with a partner, and relationship discord.

The anatomical course of the pudendal nerve makes compression a likely contributor to nerve injury, with the majority of cases produced by pudendal nerve entrapment due to birth-related difficulties, trauma or surgical sequelae, iatrogenia, intense bicycling, sacroiliac spinal deviation, and age-related changes, including pelvic skeletal fractures. The nerve may be displaced or stretched during trauma to the pelvic floor and perineum during birth. Pudendal nerve entrapment may also result from previous gynecological surgery, particularly vaginal surgery for genital prolapse or incontinence, pelvic reconstructive procedures, midurethral sling procedures, and vaginal mesh reconstructive procedures. These surgical techniques can produce direct nerve stretching or entrapment and hematomas. Pelvic skeletal fractures in the setting of osteoarthritis and osteoporosis are a common problem, and it is well known that postmenopausal women are at high risk for these conditions. PN may be related to urogenital atrophy and the decreased collagen support that accompanies lower estrogen levels during the second half of life.

Clinical characteristics of PN include pelvic pain with sitting that increases throughout the day and decreases with standing or lying down. Pain may also be relieved by sitting on a toilet seat. Patients frequently complain of burning pain and may also experience tingling, aching, stabbing, and shock-like pain. Pain distribution may be limited or extensive and may include the vulva, vagina, clitoris, perineum, and rectum in females and the glans penis, scrotum, perineum, and rectum in males. Pain may also be felt outside the “territory” of the pudendal nerve innervation. Coccygeal pain and referred pain in the calf, foot, and toes are frequent complaints. Patients may experience vague, neuropathic pain in the lower abdomen, posterior and inner thigh, or lower back.

The pudendal nerve is a mixed nerve, with sensory, motor, and autonomic functions. As a result, inflammation or injury to the nerve can also result in bowel, bladder, sexual, and autonomic dysfunction. Certain mechanisms of injury may be associated with primarily sensory symptoms or motor deficits. Symptoms include urinary frequency, urgency, symptoms mimicking interstitial cystitis, painful ejaculation, dyspareunia, painful nocturnal orgasms, and persistent sexual arousal. PN may also be associated with central sensitization, resulting in allodynic pain, such as discomfort when skin comes in contact with clothing. A pelvic foreign body sensation such as sitting on a golf ball or a hot poker in the rectum also indicates central sensitization.

Anatomy

The pudendal nerve is a mixed somatic and autonomic nerve that is derived from the ventral rami of the S2 to S4 sacral spinal roots, innervating the pelvic floor muscles, external urethral and anal sphincters, and pelvic organs. The nerve exits through the greater sciatic foramen anterior to the piriformis muscle and winds posteriorly around the ischial spine and the sacrospinous ligament, medial to the pudendal vessels ( Fig. 22.1 ). The nerve then passes deep to the sacrotuberous ligament in the biligamentary tunnel (the area between the sacrospinous and sacrotuberous ligament). The biligamentary canal can act as a “clamp” to impinge the nerve and is the most common site of entrapment.

It then reenters the perineum through the lesser sciatic foramen and the pudendal (or Alcock’s) canal, comprised of the fascia of the obturator internus muscle. At this level, the pudendal nerve normally gives rise to three terminal branches: the inferior rectal nerve (also known as the inferior anal nerve), the perineal nerve, and the dorsal nerve of the penis or clitoris ( Fig. 22.2 ). However, nerve terminations are complex, and several anatomical possibilities have been previously described. Many variations in the nerve structure have been noted during surgery or anatomical dissections. The inferior rectal branch supplies the perianal skin, the external anal sphincter, and the mucous membrane of the lower half of the anal canal. The perineal nerve gives off a deep motor portion to the muscles of the urogenital triangle (the anterior half of the perineum) and two superficial sensory branches, the medial and lateral posterior labial or scrotal nerves. The dorsal nerve of the clitoris/penis extends along the dorsum of these organs, supplying the overlying skin. PN may affect either the entire genital innervation or some of its branches.

Compression of the pudendal nerve is visible to the surgeon during decompression and transposition surgeries. The degree of compression may be severe. Congenital compression is common and observed when aberrant fascias are found and when the nerve travels through the sacrotuberous ligament. A hypertrophied obturator internus muscle may also compress the nerve in the pudendal canal. In one study, a higher pain intensity was associated with damage to the dorsal nerve of the clitoris, with sensory deficit at S2 to S4 on the dermatome map, and with a higher rate of C-fiber damage. These variables were classified as bad prognostic factors.