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Anterior cutaneous nerve entrapment syndrome

A.C.N.E.S

What is ACNES?

Abdominal cutaneous nerve entrapment syndrome (ACNES) is one of the postulated and now recognised causes of chronic abdominal pain. It remains an overwhelmingly underdiagnosed condition and consequently not readily managed. It is generally characterised by patients presenting with a severe, often refractory, chronic pain just lateral (next to) the midline. It is theorised that the cutaneous branches of the lower thoracoabdominal intercostal nerves are ‘trapped’ at the lateral border of the rectus abdominis muscle. 

What are the symptoms?

Pain is experienced just next to the middle of the abdomen either on the right or the left side from the ribs down to just above the groin. The pain can radiate to the back, up and down the abdominal wall and is not related to any gastrointestinal symptoms such as diarrhoea, constipation or altered bowel habit with or without weight loss. The prevalence of the syndrome ranges between 15% and 30% depending on the definition and the diagnostic criteria used. In adolescents, it is reported to be diagnosed in one out of eight cases of chronic abdominal pain. In the emergency department, the prevalence of ACNES in the patients presenting with acute abdominal pain has been reported to be a mere 2% of cases.

Clinically when examining a patient pain at the point of tenderness can be palpated when the abdomen is soft and then if the patient is asked to ‘sit up’ and hold this position; if this makes the pain worse then this is a positive Carnett’s test, if not then the test is negative.

It is important to exclude an underlying abdominal or gastrointestinal condition before the diagnosis of ACNES is made, therefore you may need to undergo various tests if you haven’t already done so to exclude another, sometimes missed abdominal cause of pain.

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Treatment options

Treatment initially is managed by a GI specialist clinician (gastroenterologist or a general surgeon) that will ensure that there is no other pathology present; this may involve the use of endoscopic examinations and a CAT scan of the abdomen. Injections into the muscles/nerves at the affected location of pain, can also aid in pain relief but this is generally used more so to diagnose the condition and assess as to whether surgery will be useful or not?

Pain killers are used in a step wise fashion and rely on the consultation and expertise of a pain specialist. Some of the pain killers used may be quite strong and lead to a patient becoming constipated, so the use of laxatives are also required.

Chemical treatment by using various ‘blocks’ with in some case stronger agents such as triamcinolone and botox have also shown some good results.

Surgery: is very straightforward and relies on the use of a small incision just at the point of the pain and dividing the nerves that pierce the abdominal wall to supply the overlying skin. This procedure is undertaken with the patient asleep (under general anaesthetic) with the small risks associated with the operation such as infection and bleeding of the wound. The procedure will leave a scar on the abdominal wall about 5 cm in length, but it is relatively safe as the operation does not involve going into the abdominal cavity. The surgery is undertaken as a day case so there is no overnight stay required.

Managing the pain

Diagnosis can be made when a patient presents with the following (although not all need to be present

  • Unilateral locoregional pain at the abdominal wall lasting for at least 1 month
  • The presence of a unilateral tender spot at the abdominal wall (a trigger point of <2 cm2 fingertip area of maximal tenderness, localized at the lateral border of the rectus abdominis)
  • A positive Carnett’s test
  • A positive skin pinch test and/or altered skin perception to light touch and/or cold at the area of the most intense pain
  • Normal laboratory findings with no indication of inflammation or infection, and in the absence of any surgical cause of pain
  • Negative imaging of the abdominal wall
  • Temporary positive relief in pain response of at least by 50% after injecting a local anaesthetic (usually lidocaine) at the diagnostic trigger point.

Pain is managed in a multidisciplinary fashion with the use of pain killers, injections and sometimes eventually surgery

Evidence/ Success

Large centres carrying the operation for ACNES have shown good results and quote a 70% success rate at one year. About 2/3rd of patients do get better with an improvement in their quality of life as well a reduction and in many cases cessation of pain killers they are taking.

Treatment description

  1. Pain killers including morphine in some cases
  2. Trigger point injections into the site of pain
  3. ACNES surgery

Recovery and Rehabilitation

It is important to ensure that you receive good rehabilitation advice from your treating clinician and if you have seen a physiotherapist in the past it is worth continuing with some physio and rehab after your treatment.

  1. Trigger point injections will lead to slightly more pain after the procedure with some redness possible – this will settle down in less than a week or a few days. The pain may become worse before an effect is noted. In addition the pain once resolved may recur and this can happen a week or two after the procedure or sometimes it can last longer. The procedure does not restrict any individual from carrying out their normal activities.
  2. Surgery – the small scar is a painful for a few days but this pain settles and pain killers are rarely required past four days. The wound can become inflamed and irritated, look red and also become infected. A few days course of antibiotics is all that is required if this occurs. The wound can also weep fluid and if this occurs a simple dry dressing is all that is required. Rarely the wound can fill up with fluid, this is called a seroma and resolves with pressure in time and if there is a small bleed associated with this then it is called a haematoma – very rarely a reoperation is required.

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References:

Chrona, Eleni et al. “Anterior Cutaneous Nerve Entrapment Syndrome: Management Challenges.” Journal of Pain Research 10 (2017): 145–156. PMC. Web. 30 July 2018.
Scheltinga MR, Roumen RM Anterior cutaneous nerve entrapment syndrome (ACNES) Hernia. 2018 Jun;22(3):507-516. doi: 10.1007/s10029-017-1710-z. Epub 2017 Dec 21.
van Assen T, Boelens OB et al Long-term success rates after an anterior neurectomy in patients with an abdominal cutaneous nerve entrapment syndrome Surgery. 2015 Jan;157(1):137-43. doi: 10.1016/j.surg.2014.05.022. Epub 2014 Oct 14.
Tanizaki R, Takemura Y Anterior cutaneous nerve entrapment syndrome with pain present only during Carnett's sign testing: a case report BMC Res Notes. 2017 Oct 11;10(1):503. doi: 10.1186/s13104-017-2816-1.