Anterior cutaneous nerve entrapment syndrome (ACNES) is caused by nerve entrapment in the abdominal wall. Recently de Weerd and Weum have suggested lumbar cutaneous nerve entrapment syndrome (LUCNES) as a name for a similar condition in the lower back. DIRT can potentially be used to identify the locations of perforators, thereby also indirectly identifying the location of nerve entrapment in ACNES and LUCNES, when a point of maximal pain corresponds to a hot spot. This study evaluates the location of hot spots on DIRT in relation to tender points and perforators visualized with CT angiography and color Doppler. In the ACNES patients, DIRT performed with a low-cost smartphone thermal camera will be compared to DIRT with a professional thermal camera to evaluate the usefulness of low-cost equipment to visualize the point of nerve entrapment.

Background

Anterior cutaneous nerve entrapment syndrome (ACNES) is caused by nerve entrapment in the abdominal wall. The entrapment is believed to occur at the exit point of the sensate nerve through the anterior fascia of the rectus abdominis muscle. The diagnosis is mainly based on patient history and clinical examination. Pain relief after local anaesthesia may support the diagnosis. Often patients go through many diagnostic procedures to exclude other possible causes of abdominal pain. In such, ACNES is often an exclusion diagnosis. Recently Weum and de Weerd published an article describing perforator-guided treatment of ACNES using botulinum toxin serotype A (BTA). Based on anatomical knowledge and clinical experience, they used color Doppler ultrasound (CDU) to visualize the vascular structures called perforators that accompany the nerves at the exit points through the anterior rectus fascia. They noticed that accurate placement of the needle at this exit point triggered the same pain as caused by ACNES. Their earlier publications on dynamic infrared thermography (DIRT) in perforator mapping show that the locations of perforators can be visualised as hot spots on the abdominal skin.

Based on their experimental and clinical experience, they found that lower back pain might be caused by nerve entrapment, similar as seen in ACNES. In a pilot study using CDU, they found that the point of maximal pain, as marked by the patient, corresponded with the exit point of a perforator through the lumbar fascia. Knowledge from the use of a lumbar artery perforator flap makes it very likely that the sensate nerve accompanies these perforator vessels. Recently de Weerd and Weum have suggested lumbar cutaneous nerve entrapment syndrome (LUCNES) as a name for this condition. DIRT can potentially be used to identify the locations of these perforators, thereby also indirectly identifying the location of nerve entrapment, when a point of maximal pain corresponds to a hot spot.

Although DIRT has been used in several patients as an adjunct to support the diagnosis of ACNES, there are no studies that have systematically evaluated the use of DIRT in the diagnosis of ACNES or LUCNES. If DIRT could contribute to confirm the diagnosis ACNES or LUCNES, such would be valuable for clinicians as well as patients. Today, ACNES is often a diagnosis made by excluding other causes of pain. If DIRT can be used a reliable technique in the diagnosis of ACNES and LUCNES, such would be of great psychological value to the patients and may contribute to reduced health care costs.

General practitioners are often the first health care providers that see patients with abdominal wall pain and lower back pain. Reliable perforator mapping with DIRT has until recently only been possible with expensive professional thermography equipment. Low-cost thermography cameras for smartphones are now available. If these cameras can provide reliable information on the location of perforators, and thereby also the location of nerve entrapment, general practitioners and other clinicians could use DIRT as a diagnostic tool for this patient group without expensive professional thermography equipment.

Aim and hypotheses

The aim of the study is to evaluate the usefulness of DIRT in the diagnostics of ACNES and LUCNES, as well as evaluating if inexpensive smartphone thermal cameras are equally reliable as professional thermography equipment in the diagnostics of ACNES.

Hypothesis 1: DIRT is a reliable tool to support the diagnosis of ACNES.

Hypothesis 2: DIRT is a reliable tool to support the diagnosis of LUCNES.

Hypothesis 3: Smartphone thermal cameras are equally reliable as professional thermography equipment in the diagnosis of ACNES.

Materials and methods

Patients will be recruited on a voluntary basis from the list of patients referred to the outpatient clinic at the department of plastic surgery, University hospital of North Norway (UNN), with the diagnosis ACNES or LUCNES. Only patients above the age of 18 years, that are not pregnant, with no history of allergic reactions to iodine contrast media, reduced renal function or kidney disease will be included. Based on clinical experience and previous research on perforator mapping, we estimate that 25 patients from each group will provide reliable data to evaluate the usefulness of DIRT.

Patients will be instructed to mark the location of maximal pain on their abdominal wall (ACNES) or lower back (LUCNES) with a permanent marker before arrival at the outpatient clinic. DIRT will be performed simultaneously with professional thermography equipment and a smartphone thermal camera, using the protocol described by Weum and de Weerd. Afterward the point of maximal pain will be marked with a plastic marker taped to the skin, before CTA is performed in the arterial phase. ACNES patients are examined in the supine position, and LUCNES patients in the prone position. The student will perform CDU to evaluate if the point of maximal pain corresponds with a perforator exiting the muscle fascia.

All patients recruited are referred to ultrasound-guided injection with BTA. If CDU reveals that the point of maximal pain corresponds to the exit point of a perforator, the student will perform an ultrasound-guided injection of BTA around the perforator at the exit point. The student will collect data about pain related to needle placement and injection of BTA.

All data will be analyzed with respect to the reliability of DIRT, both with professional equipment and smartphone thermal camera, to identify the location of nerve entrapment. As DIRT only provides indirect information on the point of nerve entrapment, the findings from DIRT will be compared with the findings from both CTA and CDU, which are imaging modalities that are able to visualize these exit points accurately. As an indicator of the usefulness of DIRT, the student will also evaluate the effect of BTA on the pain reported by patients three weeks after the procedure using a VAS score and quality of life assessment compared with data collected before the treatment.

As all patients have been referred for ambulatory treatment at UNN, clinical data will be stored in the electronic patient journal. Findings from the imaging modalities will be stored in the RIS and PACS system at the department of radiology. Following approval by the data protection officer at UNN, depersonalized data will be stored at secure research server and used for later analysis. Data will be stored for seven years after publication and then deleted.

Inclusion Criteria:

ACNES and LUCNES patients referred for ambulatory ultrasound-guided treatment

Exclusion Criteria:

Former reaction to contrast media used for CT angiography

25 patients with clinical signs of ACNES 25 patients with clinical signs of LUCNES