Nociceptive Processing in Acute Cutaneous Nerve Entrapment Syndrome

Study Overview
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Brief Summary
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Rationale: Chronic abdominal pain is a frequently occurring condition. Although hardly ever considered, the abdominal wall is the primary cause in 10-30% of cases. Most often it is caused by entrapment of an intercostal nerve in the anterior rectus sheath, the Anterior Cutaneous Nerve Entrapment Syndrome (ACNES). Treatment consists of local anaesthetic injections combined with methyl-prednisolon. When ineffective, a neurectomy at the site of penetration out of the ventral rectus sheet should be considered. This neurectomy however is effective in 73% of cases, leaving some 25% of patients in pain. Whether these refractory ACNES patients suffer from underlying pathologic pain disorders is subject to investigation, by using quantitative sensory testing (QST). Objective: To investigate nociceptive processing and possible underlying pathological pain processing mechanisms in ACNES patients. Study design: An observational case-control study. Study population: Patients treated for ACNES (n = 50) compared to healthy controls from an existing database. Measurements: Quantitative sensory testing (QST) of nociception, performed after treatment of ACNES for both successfully treated and refractory patients in comparison to healthy controls. Visual Analogue Scores (VAS) measured before, during and after testing procedures. Pain Anxiety Symptom Scale (PASS) and Pain Catastrophizing Scale (PCS) questionnaires. Main study parameters: Pressure pain and electrical pain thresholds as investigated by QST. Secondary study parameters are VAS-scores and results of PASS and PCS questionnaires.

Official Title
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Nociceptive Processing in Acute Cutaneous Nerve Entrapment Syndrome: a Quantitative Sensory Testing Analysis.

Conditions
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Anterior Cutaneous Nerve Entrapment Syndrome (ACNES)

Intervention / Treatment
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* Other: Quantitative Sensory Testing analysis


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patient has been diagnosed with abdominal complaints, matching ACNES: Patient had a constant site of tenderness that is superficially located with a small (<2cm2) area of maximal tenderness. The most intense pain could be localized with the tip of one finger. Tenderness increased by abdominal muscle tensing (Carnett's test). has been treated (successfully and unsuccessfully) for ACNES. Patient is at least 18 years old on the day the informed consent form will be signed. Patient is willing and able to comply with the trial protocol. Patient is able to speak, read and understand the local language of the investigational site, is familiar with the procedures of the study, and agrees to participate in the study program by giving oral and written informed consent prior to screening evaluations. Exclusion Criteria: Abdominal complaints were due to a condition other than ACNES (e.g. pain related to scar tissue). Patient has (a history of) another (chronic) pain syndrome that interferes with the interpretation of QST results. Patient has (a history of) Raynaud syndrome or fenomenon, or a medical disorder that interferes with the study measurements or may pose a risk for the patient. Patient does not feel a pinprick test to the lower extremities, due to affected sensory input (e.g. neuropathy as a result of diabetes mellitus). Female patient is pregnant during the course of the study.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| ACNES patients<br>Patients being treated in past for anterior cutaneous nerve entrapment syndrome | Other: Quantitative Sensory Testing analysis<br> <br> |
| Healthy controls<br>Healthy controls | Other: Quantitative Sensory Testing analysis<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| pressure pain threshold | The pressure pain threshold (pPT) will be determined by pressing an electronic pressure algometer, which has a surface area of 1 cm2, on a distinct muscles. The patient will be asked to say 'now' when the sensation is rated as unpleasant. The pressure will be increased at a rate of 50 kPa/sec until the pPT is reached. | > 6 weeks after treatment | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Electrical Sensation Threshold (eST) | Electrical QST will be measured using a computerized electric stimulation device delivering constant current skin stimulation via self-adhesive electrodes. Electric sensation threshold (eST): when electric sensation is first felt. | > 6 weeks after treatment | 
| Electrical Pain Threshold (ePT) | Electrical QST will be measured using a computerized electric stimulation device delivering constant current skin stimulation via self-adhesive electrodes. Electric pain threshold (ePT): when electric sensation is rated as unpleasant | > 6 weeks after treatment | 
| Electrical Pain Tolerance Threshold (ePTT) | Electrical QST will be measured using a computerized electric stimulation device delivering constant current skin stimulation via self-adhesive electrodes. Electric pain tolerance threshold (ePTT): when electric sensation is intolerable. | >6 weeks after treatment | 
| Electric Wind-Up Response (e-WUR) | Electrical QST will be measured using a computerized electric stimulation device delivering constant current skin stimulation via self-adhesive electrodes. Electric wind-up response (eWUR): rated pain after repeated stimuli | > 6 weeks after treatment | 
| Visual Analogue Scale | Patients will be asked to mark on a 100mm VAS line the average pain in a pain diary. The boundaries of these lines are no pain on the upper left site and unbearable pain on the upper right site. | > 6 weeks after treatment | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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chronic abdominal wall pain, Anterior cutaneous nerve entrapment syndrome, ACNES, CAWP