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 Table of Contents  
CASE REPORT
Year : 2020  |  Volume : 6  |  Issue : 2  |  Page : 14-18

Simple approach to a complex problem: Abdominal cutaneous nerve entrapment


Department of Anaesthesia and Intensive Care, Acharya Shri Chander College of Medical Sciences and Hospital, Sidhra, Jammu and Kashmir, India

Date of Submission16-Jul-2020
Date of Acceptance27-Oct-2020
Date of Web Publication08-Mar-2021

Correspondence Address:
Nandita Mehta
Department of Anaesthesia and Intensive Care, Acharya Shri Chander College of Medical Sciences and Hospital, Sidhra - 180 019, Jammu and Kashmir
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jrap.jrap_1_20

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  Abstract 


The aim was to show the efficacy of simple ultrasound-guided trigger point injection of local anesthetic in combination with steroid for the management of postoperative abdominal cutaneous nerve entrapment syndrome (ACNES). Abdominal cutaneous nerve entrapment can be the cause of severe, undiagnosed, abdominal pain. The entrapment of the nerve can be secondary to various conditions which cause increased abdominal pressure, leading to herniation of fat or connective tissue into the fibrous ring in the rectus abdominis muscle through which the nerve passes. Due to the compression of the nerve, there is ischemia which leads to pain. The nerve can be entrapped in scar tissue causing the compromised blood flow to the nerve and hence leading to postoperative pain. None of the available radiological investigations is helpful in diagnosing the abdominal cutaneous nerve entrapment. Clinical examination looking for tender trigger point on the abdominal wall and the eliciting a positive clinical sign, i.e., Carnett's sign can lead to the possible diagnosis of this frustrating condition. We successfully managed three cases of abdominal cutaneous nerve entrapment following laparoscopic meshplasty of abdominal hernia. All these cases were injected with a mixture of local anesthetic and steroid, i.e., 1 ml of 2% lignocaine and 1 ml of 10 mg triamcinolone at each trigger point under ultrasound guidance. The patients were prescribed pregabalin for 3 months and an anti-inflammatory COX-2 inhibitor for 10 days postprocedure. All the 3 patients were pain free at 6 months following the injections. A simple approach to a very disturbing problem of managing the severe pain due to abdominal cutaneous nerve entrapment in the postoperative period is a trigger point injection of local anesthetic and steroid under ultrasound guidance. Ultrasound-guided trigger point injections using a local anesthetic and a steroid offer an almost noninvasive option to the management of a very complex problem of ACNES.

Keywords: Abdominal cutaneous nerve entrapment, Carnett's sign, trigger point injection


How to cite this article:
Mehta N, Kaur A. Simple approach to a complex problem: Abdominal cutaneous nerve entrapment. J Recent Adv Pain 2020;6:14-8

How to cite this URL:
Mehta N, Kaur A. Simple approach to a complex problem: Abdominal cutaneous nerve entrapment. J Recent Adv Pain [serial online] 2020 [cited 2021 Jun 25];6:14-8. Available from: http://www.jorapain.com/text.asp?2020/6/2/14/310949




  Introduction Top


Abdominal wall pain is most frequently misdiagnosed pain due to lack of specific tests. This leads to unnecessary investigations, prolonged sufferings, and sometimes overtreatment that can be frustrating both for the patient and the treating physician. Abdominal cutaneous nerve entrapment syndrome (ACNES) is a condition which can be the reason for this undiagnosed abdominal pain. This syndrome is characterized by the entrapment of the cutaneous branches of the lower thoracoabdominal intercostal nerves, due to various reasons, at the lateral border of the rectus abdominis muscle, which leads to severe often refractory chronic pain. Many a times, nerve entrapment can occur in scar tissue in patients who have undergone abdominal surgery whether open or laparoscopic. This can give rise to severe abdominal pain in the late postoperative period.

Chronic abdominal pain can be a frequently presenting complaint and patients are referred to the pain physician only after the treating physician has subjected the patient to all kinds of radiological investigations and has not been able to find the real cause of pain. The patients may even unnecessarily end up undergoing diagnostic laparotomy for this pain. Very frequently, the patient's pain is labeled as psychogenic by the treating physician.

If untreated, ongoing pain leads to the development of central sensitization and ultimately becomes neuropathic. It can result in significant anxiety, distress, and loss of workdays for the patient.

The prevalence of abdominal cutaneous nerve syndrome ranges between 15% and 30% when studying the causes of chronic abdominal pain.[1],[2],[3] ACNE is the cause of pain in one out of eight cases of chronic abdominal pain in adolescents and about 2% of the patients present in the emergency with acute abdominal pain.[2],[3],[4] There is no specific age group, but it is usually seen in patients from 30 to 60 years of age. No specific diagnostic test or radiological investigation can help in pinpointing the diagnosis. A very simple clinical test, the Carnett's sign, is helpful in diagnosing the pain due to nerve entrapment. The examiner locates the point of maximum tenderness on the abdomen with his/her finger; the patient is asked either to lift the head or lift both the legs off table while the finger is kept on tender point. The patient's arms are crossed over the chest while performing this test. The worsening of pain at the point under the examiner's finger when the patient tenses the abdominal muscles shows a positive Carnett's sign. Although not very specific, the sign is mostly seen to be present in patients with entrapment of the abdominal cutaneous nerve.[1],[4] A negative Carnett's sign indicates that the pain is usually visceral in nature.



Various approaches have been tried to manage this frustrating condition ranging from pharmacological agents, trigger point injections, neuromodulation, and even surgeries like neurectomy.

We managed a series of cases (3 in number) who were referred to our pain clinic with persistent pain in the postoperative period following laparoscopic hernia repair surgeries. All these three patients were thought to be suffering from anterior cutaneous nerve entrapment syndrome. We gave ultrasound-guided trigger point injection of local anesthetic with triamcinolone.

The technique of block injection – After the localization of trigger point (point of maximum tenderness), a high-frequency linear transducer 12L-RS ultrasound probe using a GE medical systems ultrasound (GE LOGIQ E) machine was used to identify various structures on the abdominal wall like the layers of abdominal wall, the lateral border of rectus abdominis, linea semilunaris laterally, and the peritoneum below [Figure 1]. Then, the probe was moved and positioned in the transverse plane almost over the painful point. Using the in-plane technique with lateral to medial approach, the 23G spinal needle was advanced till the most painful point. Care was taken to place the tip of the needle just below the anterior rectus sheath and not into the muscle bulk. Each point was injected with 1 ml of 2% lignocaine + 1 ml of triamcinolone 10 mg, ensuring proper hydrodissection was achieved with needle manipulation.
Figure 1: Ultrasonographic view of the rectus abdominis for trigger point injection. RS: Rectus sheath, FC: Fibrous canal, LS: Linea semilunaris, ARS: Anterior rectus sheath, PRS: Posterior rectus sheath

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  Case series Top


Case 1

A 42-year-old female, who underwent laparoscopic hernia repair 8 months back, presented with chief complaints of abdominal wall pain. The pain was constant, sharp, and well localized to a point in the paraumbilical region on the right side for 6 months with a visual analog score (VAS) of 7 [Figure 2]. The pain got aggravated on forward bending and on getting up from the bed. She had been taking analgesics off and on but with not much relief. Ultrasonography (USG) done was normal except minimal interloop fluid in the iliac region.
Figure 2: The marked trigger point on the anterior abdominal wall in the right paraumbilical region

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On examination, there were multiple small scar marks on the abdomen. Local tenderness was present in the paraumbilical region at one particular point on the right side with mild hyperalgesia and Carnett's sign was positive.

We gave an ultrasound-guided trigger point injection as described. The patient was prescribed tablet etoricoxib for 10 days and capsule pregabalin 75 mg + nortriptyline 10 mg once daily to be continued for 3 months. At the first follow-up visit, after 1 week, the patient was very comfortable and >80% pain had resolved with a VAS score of 2 with no tenderness at any point on the abdominal wall. The patient was followed up at 6 weeks, 3 months, and then 6 months. She was very comfortable with no pain all through.

Case 2

A 68-year-old male with a history of laparoscopic meshplasty for umbilical hernia repair 6 months back presented with chief complaints of sharp and intolerable pain abdomen for the past 3–4 months. There were two painful points on the right side of the abdomen near the umbilicus for the past 3 months. His pain got aggravated on walking, prolonged sitting, and on changing the posture while lying down. His sleep was disturbed and could not attend his work ever since the surgery. The patient had been taking some analgesics, but there was no relief of pain. Ultrasound and computed tomography (CT) scan done were unremarkable and the patient was referred to the pain clinic. There was no complaint of numbness or tingling sensation and the VAS score was 8. On examination, there was marked tenderness at two distinct points in the supraumbilical region on the right side, and there was no allodynia or hyperalgesia. Carnett's sign was a positive for both the points. The patient received USG-guided two trigger point injections by in-plane technique using 1 ml triamcinolone (10 mg) + 1 ml of 2% lidocaine. In addition, the patient was prescribed anti-inflammatory tablet etoricoxib (60 mg) OD for 10 days and pregabalin (75 mg) + nortriptyline (10 mg) at bedtime for 3 months. At the first follow-up visit, after 1 week, the patient was comfortable and there was >70% pain relief with VAS score of 3. On the second follow-up visit, after 6 weeks, the patient was completely pain free in the right supraumbilical region. The patient presented to the clinic again after 2 months of the trigger point injection and complained of excruciating pain in the left supraumbilical area for the last 8 days. There was marked tenderness on one point on the left side with a positive Carnett's test with a VAS score of 9. USG was repeated again which did not show any fluid collection. An ultrasound-guided trigger point injection was given in the left supraumbilical region at the trigger point. In addition, the patient was advised to continue capsule pregabalin + nortriptyline (10 mg) for 3 months. Following trigger point injection in the left supraumbilical region, at 1 week, the pain got relieved by 70% following the injection with a VAS score of approximately 2 and was completely pain free at 6 weeks, 3, and 6 months after the second trigger point injection.

Case 3

A 57-year-old female presented with chief complaints of pain for 6 months at three distinct sites on the anterior abdominal wall after laparoscopic meshplasty which was done 7 months back. The pain started immediately after removing the abdominal corset (binder) after 1 month, which was advised by the surgeon to be worn in the immediate postoperative period. As the patient had some relief of pain with the corset, she continued the use of the corset all through the day, for a prolonged period (6 months) without seeking any consultation with the surgeon. The patient got severe, continuous pain every time she tried to remove the abdominal binder. Pain especially got aggravated on walking, straining, and changing posture during lying down. The patient was afebrile with no local redness or induration at all the three painful points on the anterior abdominal wall. There was marked hyperalgesia and allodynia. The VAS score was 9 and the Carnett's test was positive for all the three points, i.e., two distinct points on the right side in the supraumbilical region and one on the left side of the umbilicus. USG findings were not remarkable. Ultrasound-guided trigger point injection was given at all the three points using 1 ml triamcinolone (10 mg) + 1 ml of 2% lignocaine at each point. In addition, the patient was prescribed tablet etoricoxib (60 mg) OD for 10 days and pregabalin (75 mg) twice a day, and nortriptyline (10 mg) at bedtime for 3 months. During the first follow-up visit, after 1 week, the patient was comfortable with 60% pain relief and a VAS score of 4. Hyperalgesia and allodynia were markedly decreased and the patient was comfortable without the abdominal binder. At 6 weeks post procedure, the patient had good pain relief and remained comfortable both at 3 months and 6 months.


  Discussion Top


Postoperative abdominal pain in most cases is often related to intraabdominal etiologies. As a result, the abdominal wall is often ignored as a potential source of abdominal pain. ACNES was first described in 1972 by Applegate.[5] Hall and Lee suggested 15% of nonspecific abdominal pain originate from the abdominal wall.[6]

The abdominal wall is supplied by the abdominal branches of lower intercostal nerves from T7 to T12. They travel downward between the muscle layer to the lateral border of the rectus abdominis muscle. Close to the lateral border of the rectus muscle, they change direction making an acute turn almost at 90° before traversing through neurovascular fibrous channels which are like fibrous rings in the muscle. Then, the nerves reach the anterior surface of the muscle and take a 90° turn before they terminate by supplying the skin [Figure 3].
Figure 3: The course of abdominal cutaneous nerve after turning at 90° before entering and exiting the fibrous canal in rectus abdominis muscle. RA: Rectus abdominis, Ant RS: Anterior rectus sheath, Post RS: Posterior rectus sheath

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Main reason of the pain is because of entrapment of abdominal wall cutaneous nerve which occurs due to compression of nerve inside the fibrous channels. This may be caused by changes in intraabdominal pressure which leads to the herniation of either connective tissue or fat or scar tissue through the ring causing nerve compression and ultimately nerve ischemia. Nerve ischemia causes severe pain which when persistent results into neuropathic pain.[7],[8]

A detailed history followed by simple physical examination can help in differentiating abdominal wall pain from intraabdominal visceral pain. The patient will complain of sharp pain, mostly at the lateral border of the rectus that can be localized using a single finger and is mostly aggravated on increasing pressure on the abdominal wall like flexion. Pain shows no relation with the food habits of the patient. Scarring from previous surgical manipulations and increased intraabdominal pressure are the important factors that contribute to abdominal cutaneous nerve entrapment. On USG, abdominal cutaneous nerves can be seen as hyperechoic oblique lines traversing through the rectus abdominis muscle [Figure 1].

Various treatment modalities have been tried for ACNES like pharmacological treatment which includes analgesics like nonsteroidal anti-inflammatory drugs and weak opioids. As the pain of ACNES is mainly mechanical, so these drugs are less effective. Furthermore, if the pain remains undiagnosed for a long time, there occurs central sensitization, so this pain becomes chronic and neuropathic which is even more difficult to manage with analgesics.[7] In order to have good pain relief and improve patient's comfort, it is always helpful to administer co-analgesics like pregabalin (anticonvulsant) as we did in all the three patients.

Various intervention options for the management of abdominal wall cutaneous nerve like botulinum toxins, chemical neurolysis, radiofrequency ablation, neuromodulation with pulse radiofrequency and neurectomy have been tried. Botulinum toxin injection is expensive and multiple injections (5–30) may be required in the first sitting which needs to be repeated after 3–4 months. More studies are needed to decide regarding their effectivity.[8] Radiofrequency ablation can be done after getting good pain relief with two diagnostic trigger point injection using two different local anesthetics. Neuromodulation can be offered to patients who do not get pain relief with any of the methods including surgical neurectomy. Again it is very expensive and an invasive procedure which is available in few centers and its efficacy in the management of ACNES is unproven.[9] Chemical neurolysis can be done with either absolute alcohol or phenol, but their long-term effect is not certain, and it may lead to deafferentation pain, hence is not preferred.[7]

Neurectomy is a very invasive procedure, and mostly, it is difficult to pinpoint the nerve involved so the results can be sometimes frustrating. Hence, it is usually reserved for refractory cases and it can also lead to deafferentation pain.[7]

A simple approach to this disturbing problem is a trigger point injection which has been tried by many workers both as diagnostic and therapeutic. Previously, the most commonly used approach for trigger point injection was a blind one. In a study by Boelens et al., the trigger points were blindly injected either with local anesthetic or saline. Patients in the saline group also had long-lasting pain relief, probably due to hydrodissection and release of adhesions around the nerve.[10]

With the use of ultrasound, the trigger point can be injected and the drug deposited just below the rectus sheath or into the fibrous channel carrying the abdominal cutaneous nerve.[11],[12] An ultrasound was used in our patients to ensure the deposition of injectate just below the anterior rectus sheath and not in the muscle bulk. As with steroids injection in the muscle, there is always a risk of muscle atrophy. The addition of corticosteroids may lead to a more persistent pain relief, possibly owing to its anti-inflammatory action, and the provoked attenuation of ectopic firing. The trigger point injection sometimes fails to achieve adequate results which can be attributed either to incorrect diagnosis or difficulty in locating the trigger points as seen in obese patients.


  Conclusion Top


Although abdominal cutaneous nerve entrapment is a difficult to diagnose condition, should always be kept as a differential in patients of postoperative abdominal pain. A simple injection of trigger point with local anesthetic agent and steroid can be both diagnostic and therapeutic. A minimally invasive technique in the form of an ultrasound-guided injection of the trigger point can provide long-lasting pain relief without requiring any other intervention. At the same time, it is important to prescribe co-analgesics in order to address the neuropathic component.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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2.
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3.
Applegate WV. Abdominal cutaneous nerve entrapment syndrome (ACNES): A commonly overlooked cause of abdominal pain. Perm J 2002;6:20-7.  Back to cited text no. 3
    
4.
van Assen T, Brouns JA, Scheltinga MR, Roumen RM. Incidence of abdominal pain due to the anterior cutaneous nerve entrapment syndrome in an emergency department. Scand J Trauma Resusc Emerg Med 2015;23:19.  Back to cited text no. 4
    
5.
Applegate WV. Abdominal cutaneous nerve entrapment syndrome. Surgery 1972;71:118-24.  Back to cited text no. 5
    
6.
Hall PN, Lee AP. Rectus nerve entrapment causing abdominal pain. Br J Surg 1988;75:917.  Back to cited text no. 6
    
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Chrona E, Kostopanagiotou G, Damigos D, Batistaki C. Anterior cutaneous nerve entrapment syndrome: Management challenges. J Pain Res 2017;10:145-56.  Back to cited text no. 7
    
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Weum S, de Weerd L. Perforator-guided drug injection in the treatment of abdominal wall pain. Pain Med 2016;17:1229-32.  Back to cited text no. 8
    
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Kleef MV, Stolker R, Lataster A, Geurts J, Benzon H, Mekhail N. Thoracic pain. In: Van Zundert J, editor. Evidence-Based Interventional Pain Management: According to Clinical Diagnosis. Chichester, UK: Wiley-Blackwell; 2012. p. 62-70.  Back to cited text no. 9
    
10.
Boelens OB, Scheltinga MR, Houterman S, Roumen RM. Randomized clinical trial of trigger point infiltration with lidocaine to diagnose anterior cutaneous nerve entrapment syndrome. Br J Surg 2013;100:217-21.  Back to cited text no. 10
    
11.
Kanakarajan S, High K, Nagaraja R. Chronic abdominal wall pain and ultrasound-guided abdominal cutaneous nerve infiltration: A case series. Pain Med 2011;12:382-6.  Back to cited text no. 11
    
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Mangal D, Manocha A, Sharma P, Singh MK. Pinning the pain: A case of anterior cutaneous nerve entrapment. Indian J Pain 2019;33:42-4.  Back to cited text no. 12
    


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  [Figure 1], [Figure 2], [Figure 3]



 

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