ACNES is a neuropathic pain condition of the abdominal wall. It is a clinical diagnosis based on patient's history and physical examination. No diagnostic test is available to confirm the diagnosis.

This pilot study will determine if skin biopsies can be used as diagnostic test. Two 3mm biopsies will be taken and used to count the small nerve fibres in the skin. The number of small nerve fibres of the painful skin will be compared to non-painful skin. Skin biopsy and small fibre nerve count is already used as diagnostic test in patients with small-fibre neuropathy.

The investigators hypothesize that patients with ACNES will have a reduced number of small nerve fibres in the affected skin, compared to the non-affected skin.

Inclusion Criteria:

• Duration of pain >3 months
• Newly diagnosed unilateral ACNES
• Fully completed intake questionnaire
• Obtained written informed consent

Exclusion Criteria:

• Inability to understand Dutch language

• Bilateral ACNES

• Previously administered injections with corticosteroids at trigger point (injection with a local anaesthetic is allowed)

• Previous Pulsed Radiofrequency (PRF)-treatment at trigger point

• History of open abdominal surgery

• History of neurectomy

• Known neuromuscular or neurodegenerative disease

• Antiplatelet or anticoagulants use or known coagulation disorders

• Disorder known to cause a reduced IENFD;

  • Diabetes
  • Hypothyroidism
  • Renal failure
  • Vitamin B12 deficiency
  • Monoclonal gammopathy
  • Alcohol abuse (>5 IU a day)
  • Malignancies
  • Medication that cause neuropathy (for example chemotherapy)

The pathologists who will measure the nerve fibre density are blinded; they will not know if the biopsy is from the affected or non-affected side.