Anterior cutaneous nerve entrapment syndrome (ACNES) is a

nerve entrapment Nerve compression syndrome, or compression neuropathy, or nerve entrapment syndrome, is a medical condition caused by chronic, direct pressure on a peripheral nerve. It is known colloquially as a ''trapped nerve'', though this may also refer to n ...

condition that causes

chronic pain Chronic pain is pain that persists or recurs for longer than 3 months.https://icd.who.int/browse/2025-01/mms/en#1581976053 It is also known as gradual burning pain, electrical pain, throbbing pain, and nauseating pain. This type of pain is in cont ...

of the

abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity. The abdominal wall is split into the anterolateral and posterior walls. There is a common set of layers covering and forming all the walls: the deepest being the vi ...

. It occurs when nerve endings of the lower

thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...

intercostal nerves The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and dif ...

(7–12) are 'entrapped' in

abdominal muscle The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

s, causing a severe localized nerve (neuropathic) pain that is usually experienced at the

front Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * '' The Front'', 1976 film Music * The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ...

of the abdomen. ACNES is frequently overlooked and unrecognized, although the incidence is estimated to be 1:2000 patients. The relative unfamiliarity with this condition often leads to significant

diagnostic delay Diagnostic delay is the time interval between the onset of symptoms and confirmed diagnosis of a disease. For a variety of reasons, including the mitigation of disease severity and financial expense, it is desirable for this delay to be minimized. ...

s and misdiagnoses, often resulting in unnecessary diagnostic interventions and futile procedures. Physicians often misdiagnose ACNES as

irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...

appendicitis Appendicitis is inflammation of the Appendix (anatomy), appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, fever and anorexia (symptom), decreased appetite. However, approximately 40% of people do not have these t ...

as symptoms of the condition are not unique to this syndrome.

Signs and symptoms

Affected individuals typically experience limited relief from standard pain relieving medication, with the exception of some

neuroleptic Antipsychotics, previously known as neuroleptics and major tranquilizers, are a class of psychotropic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizoph ...

agents. Patients frequently experience 'pseudovisceral' phenomena or symptoms of altered

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

function including nausea, bloating, abdominal swelling, loss of appetite with consecutively lowered body weight or an altered defecation process. Pain is typically related to tensing the abdominal wall muscles, so any type of movement is prone to aggravate pain. Lying quietly can be the least painful position. Most patients report that they cannot sleep on the painful side.

Cause

In terms of etiology we find that it is due to the entrapment of cutaneous end branches of intercostal nerve in muscular foramen. This in turn causes ischemic neuropathy.

Diagnosis

Once ACNES is considered based on the patient's history, the diagnosis can be made via a thorough physical examination: looking for a painful spot, which worsens by tensing the abdominal muscles with lifting the head and straightened legs (

Carnett's sign In medicine, Carnett's sign is a finding on clinical examination in which ( acute) abdominal pain remains unchanged or increases when the muscles of the abdominal wall are tensed. For this part of the abdominal examination, the patient can be aske ...

). Almost always, a small area of maximal pain is covered by a larger area of altered skin sensibility with

somatosensory The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...

disturbances such as

hypoesthesia Hypoesthesia or numbness is a common side effect of various medical conditions that manifests as a reduced sense of touch or sensation, or a partial loss of sensitivity to sensory stimuli. In everyday speech this is generally referred to as nu ...

as well as

hyperesthesia Hyperesthesia is a condition that involves an abnormal increase in sensitivity to stimuli of the senses. Stimuli of the senses can include sound that one hears, foods that one tastes, textures that one feels, and so forth. Increased touch sensi ...

hyperalgesia Hyperalgesia ( or ; ''hyper'' from Greek ὑπέρ (''huper'') 'over' + ''-algesia'' from Greek ἄλγος (algos) 'pain') is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and ...

and change of cool perception. Pinching the skin between thumb and index finger is extremely painful compared to the opposite non-involved side. Confirmation of a diagnosis of ACNES is warranted using an abdominal wall infiltration with a local anesthetic agent near the painful spot.

Treatment

Treatment consists of several such anesthetic injections, sometimes combined with

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

s. Such an approach yields persistent pain relief in two-thirds of patients. This beneficial effect on pain has been demonstrated in a prospective double blind trial. The physical volume of the injection may also break apart the adhesions or fibrosis responsible for the entrapment symptoms. Patients who do not respond to a stratagem of repetitive local trigger point injections can be offered a surgical approach. Terminal branches of an intercostal nerve are removed at the level of the anterior sheath of the rectus abdominal muscle (' anterior neurectomy'). Several larger series demonstrated a successful response in approximately two out of three patients, which was confirmed in another prospective double blind surgical trial: 73% of the patients who underwent a neurectomy were pain free, compared to 18% in the non-nerve resected group. Patients not responding to an anterior neurectomy, or those in whom the pain syndrome recurs after an initial pain free period (10%) may choose to undergo secondary surgery. This involves a repeated exploration combined with a posterior neurectomy. This procedure has been shown to be beneficial in 50% of cases.

Epidemiology

This syndrome is predominantly found in young women, but may occur in both sexes and all age groups.

References

{{Reflist Chronic pain syndromes