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CASE REPORT

CASE REPORT

Chronic Pelvic Pain Due to Peripheral Neuropathy: A Case Report

Shyam Balasubramanian, MBBS, MD, FRCA,1 Patricia Morley-Forster, MD, FRCPC2

1 2

Clinical Fellow, Interdisciplinary Pain Program, Schulich School of Medicine, University of Western Ontario, London ON Medical Director, Interdisciplinary Pain Program, Schulich School of Medicine, University of Western Ontario, London ON

Abstract

Background: There are numerous possible causes for chronic pelvic pain. Evaluation of these causes should begin with the least invasive form of assessment. Case: A 28-year-old woman with chronic pelvic pain underwent an array of investigations and surgical interventions without relief of pain. When she was admitted to hospital because of a flare up of pelvic pain, the chronic pain service was consulted. The presentation of stabbing pain that was reproduced by eliciting focal tenderness over the course of ilioinguinal nerve made nerve entrapment a possible diagnosis. An ilioinguinal nerve block was performed, resulting in resolution of the pain. Conclusion: Chronic pelvic pain due to peripheral neuropathy can mimic visceral pain, presenting a diagnostic challenge.

of pathologic causes, and it may occur in individuals with no apparent physical abnormalities. About 40% of laparoscopies are performed to evaluate CPP.2 The neuropathy arising from entrapment of the ilioinguinal nerve is a possible cause. The mean delay in diagnosing this condition may be as long as 12 months.3 Having knowledge of this condition can prevent unnecessary investigation and delay in treatment.

THE CASE

Résumé

Contexte : La douleur pelvienne chronique compte de nombreuses causes possibles. L'évaluation de ces causes devrait commencer par la forme d'examen la moins invasive. Cas : Une femme de 28 ans présentant une douleur pelvienne chronique a été soumise à un ensemble d'explorations et d'interventions chirurgicales, sans pour autant obtenir un soulagement de la douleur. Lorsqu'elle a été hospitalisée en raison d'une flambée de douleur pelvienne, le service de douleur chronique a été consulté. La présentation d'une douleur en coup de poignard, reproduite par le déclenchement d'une sensibilité en foyer le long du petit nerf abdomino-génital, a fait en sorte que la compression chronique a été considérée à titre de diagnostic possible. Un bloc du petit nerf abdomino-génital a été effectué, ce qui a entraîné la résolution de la douleur. Conclusion : La douleur pelvienne chronique attribuable à une neuropathie périphérique peut imiter la douleur viscérale, ce qui constitue un défi sur le plan du diagnostic. J Obstet Gynaecol Can 2006;28(7):603­607

A 28-year-old woman was referred to the chronic pain service with an 18-month history of pelvic pain. Her background problems included polycystic ovaries, obesity (BMI 43 kg/m2), asthma, and depression. She had undergone Caesarean section nine years previously and laparoscopic cholecystectomy seven years previously. The pain had begun spontaneously 18 months prior to admission. It involved the lower abdomen, more markedly the right lower quadrant than the left. The intensity of the pain gradually increased. The patient underwent a series of investigations, including blood tests, computerized tomography of the pelvis, ultrasound examinations, laparoscopy, and hysteroscopy, none of which identified the cause of the pain. Hysterosalpingography was attempted but was abandoned because of the intense pain. The patient was admitted to hospital for investigation and treatment, and the chronic pain service was consulted. The patient described the pain as continuous, intense, and stabbing. It was located in the pelvic region, was felt more on the right side than the left, and was aggravated by having a full bladder, by menstruation, and by sitting upright. It was severe enough to limit mobility but was partially relieved by local application of heat or by lifting the abdominal panniculus. The patient had previously used oxycodone, acetaminophen, and nonsteroidal anti-inflammatory agents

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INTRODUCTION

C

hronic pelvic pain (CPP) in women is a debilitating condition that is responsible for substantial suffering and health care expenditure.1 It can arise from a variety

Key Words: Chronic pelvic pain, entrapment neuropathy Competing Interests: None declared. Received on December 20, 2005. Accepted on February 28, 2006

CASE REPORT

with little benefit. She was taking venlafaxine 75 mg daily for treatment of depression. Following admission to hospital, she was offered patient-controlled analgesia (PCA) using morphine. Her score on the analogue pain-rating scale remained 10/10 at rest, despite the use of PCA with administration of morphine 10 mg per hour. On examination, the patient was moderately distressed by the pain. The abdomen was soft with no palpable masses; there was decreased sensation to pinprick over the Pfannenstiel scar, which was hidden by the abdominal panniculus. The pain was reproduced by palpating the scar along the course of the ilioinguinal nerve, more on the right side than the left. There was no allodynia or hyperalgesia in the area involved. We suspected that the patient's CPP resulted from a peripheral neuropathy following entrapment of the ilioinguinal nerve. Thus, a diagnostic and therapeutic nerve block was performed using 20 mL of 0.25% bupivacaine and 40 mg of methylprednisolone to block the right ilioinguinal nerve and tender areas in the scar. Within minutes, the patient's rating of pain on the analogue scale had fallen to zero, and she was able to sit up and walk without pain. Treatment subsequently began with pregabalin 75 mg twice daily, and over the next few days she discontinued the use of opioids. Three months later the patient reported a recent recurrence of lower abdominal pain, this time more on the left side than the right, but milder than during the original presentation. Bilateral ilioinguinal nerve block was again performed with bupivacaine and methylprednisolone. Her pain rating score has since remained at less than 2/10, even with exertion. She continues to attempt to reduce weight.

DISCUSSION

tissue. Although these mechanisms can produce pain immediately in the postoperative period, the onset of pain can also occur many years after the original surgery.4,6 Bilateral idiopathic entrapment neuropathy involving ilioinguinal nerves, with no obvious cause for entrapment, has also been reported.7 The patient in the present case was obese and had gained more weight in the two to three years before the onset of pain. A protruding, pendulous abdomen can push the inguinal ligament anteriorly and inferiorly, dragging the inguinal nerves with it and contributing to entrapment neuropathy. Although this mechanism is commonly described in meralgia paresthetica (involving the lateral femoral cutaneous nerve deep to the inguinal ligament), it can also involve other nerves in that area. In a series of groin neuropathy that included 35 patients with ilioinguinal nerve involvement causing groin pain who underwent surgical management, two of the patients with poor results had a large abdominal panniculus.8 In another series of patients with nerve entrapment treated with neurolysis, the only patient who failed to respond to the treatment had a large panniculus.9 In both of these series, the pain was relieved when the respective procedures were combined with panniculectomy. The patient's pain was exacerbated when the bladder was full and during menstruation. Consequently, visceral pathologies including urinary tract infection, endometriosis, and polycystic ovaries were suspected but ruled out. The phenomenon of "viscero-somatic convergence" makes discrimination of somatic and visceral pain difficult.10 Somatic (abdominal wall) nerves and visceral nerves relay pain signals through the same dorsal horn segment in the spinal cord. The second order neurons from the transmission cells in the dorsal horn segment relay the signal to the brain. Consequently, the brain perceives the sensation of pain as coming from a single dermatome level but does not distinguish between somatic and visceral origins. In addition, menstruation can exacerbate neuropathic pain by means of perineural edema, hormone-induced increases in neurotransmitter activity, or dorsal horn sensitivity.4 Clinicians not familiar with the phenomenon of entrapment neuralgia may conclude that the reported symptoms have a psychosomatic basis. Psychological factors may exacerbate the pain response, but only rarely is somatization a cause of pain. Neurological complications after pelvic surgery are often transient and generally resolve spontaneously with minimal intervention, although long term disability occasionally occurs.11 Ilioinguinal and iliohypogastric nerves are at risk for entrapment. Both the nerves originate from the lumbar plexus, pass together through the psoas muscle, and extend diagonally along the ventral surface of the quadratus

Chronic pelvic pain is often assumed, by patients and physicians alike, to be visceral in origin.4 Being aware that peripheral neuropathies may cause CPP may avoid inappropriate investigations and unhelpful surgical interventions. The etiology of such a peripheral neuropathy can vary; possibilities include nerve stretch, obesity, repetitive minor injuries, blunt trauma, and surgical incisions. The patient described here had undergone a Caesarean section with a transverse lower abdominal incision more than nine years before the onset of pain. The incidence of postoperative neuropathy following major pelvic surgery has been reported to be 1.9%,5 and the prevalence of nerve entrapment in patients following a Pfannenstiel incision for various surgical procedures has been reported as 3.7%.6 Nerve entrapment can result from neuroma formation after damage to the nerve, incorporation of the nerve by a suture, or tethering or constriction of the nerve in surrounding scar

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Chronic Pelvic Pain Due to Peripheral Neuropathy: A Case Report

Left Inguinal Region a. pubic symphysis b. ilioinguinal nerve c. superficial inguinal ring d. inguinal ligament e. internal oblique muscle f. anterior superior iliac spine g. external oblique aponeurosis h. iliohypogastric nerve

lumborum muscle caudally to the iliac crest. Both nerves thereafter continue towards the deep inguinal ring on the inner surface of the transversus abdominis muscle. They then pass through this muscle to run between it and the internal oblique muscle for a short distance, eventually piercing the internal oblique to run between it and the external oblique muscle. The ilioinguinal nerve courses through the inguinal canal and superficial inguinal ring. The location of the ilioinguinal nerve in the inguinal canal and the distribution pattern of cutaneous branches in the inguinal region can be variable.12 Commonly, the ilioinguinal nerve provides cutaneous sensation to the groin, pubic symphysis, labium majus, and upper inner thigh (see Figure). The ilioinguinal, iliohypogastric, and genitofemoral nerves may

share interconnecting fibres. Precise identification of the entrapped nerve may therefore be difficult, as the sensory field of the nerve varies widely.13 Clinical diagnosis relies on a high index of suspicion. The diagnostic triad of nerve entrapment or neuroma after surgery comprises (1) sharp, burning, or lancinating pain near the incision that radiates to the area supplied by the nerve; (2) evidence of impaired sensory perception in the area of distribution of the nerve; and (3) pain that is relieved by infiltration with local anaesthetic.14 Seeking to elicit Tinel's sign (reproducing the pain by tapping the nerve along its course) is also recommended. Tenderness that originates inside the abdominal cavity usually decreases when a supine patient tenses the abdominal wall by lifting head and

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CASE REPORT

shoulders off the examining table. In contrast, pain arising from the abdominal wall is unchanged or increased by this manoeuvre (constituting a positive Carnett's sign).15 Taking a history and performing a physical examination are usually sufficient to determine whether the pain is referable to one or more of the inguinal nerves.8 The value of nerve conduction studies in ilioinguinal neuropathy is uncertain because they have not been validated in patients. Electromyography has been used to diagnose ilioinguinal neuropathy,16 and magnetic resonance neurography is undergoing evaluation for assessment of the peripheral nervous system.17 Although the latter technology has been used with large nerves such as the sciatic nerve and brachial plexus, its value in the diagnosis of entrapment of smaller nerves such as the ilioinguinal has not been established. The diagnosis of peripheral nerve entrapment therefore remains clinical, and we must acknowledge that in the present case there is a degree of diagnostic uncertainty. Ilioinguinal nerve block with a local anaestheticcorticosteroid mixture for desensitization is a recognized treatment for this neuropathy. Serial nerve blocks are often required and may provide permanent cure.18 Nevertheless, there are no placebo-controlled studies to support the use of these diagnostic and therapeutic blocks. The prolonged distress and suffering in patients with chronic pain and the invasiveness of nerve blocks may prevent clinicians from justifying the inclusion of placebo in their research studies.19 The nerve blocks can at times lead to erroneous interpretation, because it is possible that patients with more distal pathologies may experience similar pain relief. Several factors, such as observer error, placebo effect, and bias induced by patient expectations, confound the interpretation of studies on the usefulness of neural blockade in the diagnosis of chronic pain.20 In the present case, we acknowledge that the possibility of a placebo response requires that we interpret the apparent effect of nerve block with caution. Pharmacologic therapy for neuropathic pain includes use of tricyclic antidepressants, such as amitriptyline and nortriptyline, or use of anticonvulsants, such as pregabalin. Because neuropathic pain arises from several distinct mechanisms, each requiring specific treatment, conclusions about responsiveness to opioids may vary.21 The specific mechanism of action of pregabalin in ameliorating neuropathic pain is unknown. It possibly acts by binding to calcium channels and modulating calcium influx, thereby reducing the release of neurotransmitters such as glutamate, norepinephrine, and substance P. Although use of gabapentin has been reported to show benefit in neuropathic pain conditions, its pharmacokinetics are non-linear and it typically requires slow titration to reach an

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effective dose. Pregabalin achieves efficacy at lower doses, and has an increased therapeutic index and fewer dose-related side effects.22 Treatment using serial nerve blocks for desensitization and medical therapy should be attempted before resorting to surgical interventions. Other non-surgical strategies for pain resolution include biofeedback, physical therapy, and percutaneous treatment with phenol, alcohol, cryoprobes, and radiofrequency destruction. When these measures fail, surgical neurolysis, neuroma resection, surgical resection of the involved nerve,13 and burying the cut end of the nerve into muscle23 have been reported. Reports claim excellent pain relief and restoration of function following surgical intervention in about 70% of patients with groin pain.8,13 Transection of the nerves may result in two challenging complications: neuroma formation and continuing pain from maladaptive neuronal plasticity.4 The length of the lower abdominal skin incision is the only factor so far identified as an independent risk for inguinal nerve entrapment. Entrapment is more common when the lower abdominal incision is extended beyond the lateral border of the rectus sheath.6 Improper positioning of self-retaining retractors may predispose to neurological injury.11 Although knowledge of the neuroanatomy of the pelvis and lower abdomen can minimize the injury, neuropathy will still occasionally occur. Early recognition and active intervention can help avoid persistent pain and permanent weakness or atrophy of the involved muscle group.5 It also prevents depression, loss of self-esteem, difficulties with sexual relations, and decreased ability to function. Further research in primary prevention by altering surgical technique may lead to a reduction in nerve entrapment.

CONCLUSION

Peripheral neuropathy contributing to chronic pelvic pain is often missed in a clinical setting. Diagnosis by careful history, physical examination, and use of nerve blocks can avoid delay in managing this potentially treatable condition.

ACKNOWLEDGEMENTS

The woman whose story is told in this case report has provided signed permission for its publication.

REFERENCES

1. Consensus guidelines for the management of chronic pelvic pain. J Obstet Gynaecol Can 2005;27(8):781­801. 2. Howard FM. The role of laparoscopy in chronicpelvic pain: promise and pitfalls. Obstet Gynecol Surv1993;48(6):357­87. 3. Knockaert DC, D'Heygere FG, Bobbaers HJ. Ilioinguinal nerve entrapment: a little-known cause of iliac fossa pain.Postgrad Med J 1989; 65(767):632­5.

Chronic Pelvic Pain Due to Peripheral Neuropathy: A Case Report

4. Perry CP. Peripheral neuropathies and pelvic pain: Diagnosis and management. Clin Obstet Gynecol 2003;46:789­96. 5. Cardosi RJ, Cox CS, Hoffman MS. Postoperative neuropathies after major pelvic surgery. Obstet Gynecol 2002;100:240­4. 6. Luijendijk RW, Jeekel J, Storm RK, Schutte PJ, Hop WC, Drogendijk AC, et al. The low transverse Pfannenstiel incision and the prevalence of incisional hernia and nerve entrapment. Ann Surg 1997;225(4):365­9. 7. Schorl M. Schweikardt B. Kaminski M. Idiopathic entrapment neuropathy of the ilio-inguinalis nerve--a differential diagnosis in inguinal pain [German]. Schweizerische Rundschau fur Medizin Praxis 2000;89(5):197­200. 8. Lee CH, Dellon AL. Surgical management of groin pain of neural origin. J Am Coll Surg 2000;191:137­42. 9. Nahabedian MY, Dellon AL. Meralgia paresthetica: Etiology, diagnosis, and outcome of surgical decompression. Ann Plast Surg 1995;35:590­4. 10. Perry CP. Peripheral neuropathies causing chronic pelvic pain. J Am Assoc Gynecol Laparosc 2000;2:281­7. 11. Irvin W, Anderson W, Taylor P, Rice L. Minimizing the risk of neurologic injury in gynecologic surgery. Obstet Gynecol 2004;103:374­82. 12. Rab M, Ebmer J, Dellon AL. Anatomic variability of the ilioinguinal and genitofemoral nerve: Implications for the treatment of groin pain. Plast Reconstr Surg 2001;108:1618­23. 13. Madura JA, Madura JA 2nd, Copper CM, Worth RM. Inguinal neurectomy for inguinal nerve entrapment: an experience with 100 patients. Am J Surg 2005;189:283­7.

14. Starling JR, Harms BA. Diagnosis and treatment of genitofemoral and ilioinguinal neuralgia. World J Surg. 1989;13:586­91. 15. Suleiman S, Johnston DE. The abdominal wall: An overlooked source of pain. Am Fam Physician 2001;64:431­8. 16. Arcocha AJ, Irimia SP, Soto O. Ilioinguinal neuropathy: usefulness of conduction studies (Spanish). Neurologia. 2004;19(1):24­6. 17. Maravilla KR, Bowen BC. Imaging of the peripheral nervous system: Evaluation of peripheral neuropathy and plexopathy. Am J Neuroradiol 1998;1011­23. 18. Sippo WC, Gomez AC. Nerve entrapment syndromes from lower abdominal surgery. J Fam Pract 1987;25:585­7. 19. Raja SN. Nerve blocks in the evaluation of chronic pain: A plea for caution in their use and interpretation. Anesthesiology 1997;86(1):4­6. 20. Hogan QH, Abram SE. Neural blockade for diagnosis and prognosis: a review. Anesthesiology 1997;86:216­41. 21. Dellemijn P. Are opioids effective in relieving neuropathic pain? Pain 1999;80:453­62. 22. Freynhagen R, Strojek K, Griesing T, Whalen E, Balkenohl M. Efficacy of pregabalin in neuropathic pain evaluated in a 12-week, randomised, double-blind, multicentre, placebo-controlled trial of flexible- and fixed-dose regimens. Pain 2005;115:254­63. 23. Otfinowski J, Pawelec A, Kaluza J. Implantation of peripheral neural stump into muscle and its effect on the development of posttraumatic neuroma. Pol J Pathol 1994;45:195­202.

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