Carnett's Sign for Anterior Cutaneous Nerve Entrapment Syndrome
The recommended diagnostic maneuver for anterior cutaneous nerve entrapment syndrome (ACNES) is Carnett's sign, which differentiates abdominal wall pain from intra-abdominal pathology by having the patient tense their abdominal muscles while the examiner palpates the tender point. 1
How to Perform Carnett's Sign
- The patient lies supine while the examiner identifies and palpates the maximal point of tenderness on the abdominal wall 1
- The patient then lifts their head and shoulders off the examination table (or performs a partial sit-up) to contract the rectus abdominis muscles while the examiner continues palpating the tender point 1
- A positive Carnett's sign occurs when pain remains the same or worsens with muscle contraction, indicating the pain originates from the abdominal wall rather than intra-abdominal structures 1
- This maneuver is particularly useful because intra-abdominal pathology typically causes pain that decreases when the abdominal wall muscles are tensed, as the contracted muscles act as a protective barrier 1
Additional Diagnostic Features
- The trigger point is typically located at the lateral border of the rectus abdominis muscle where the cutaneous branches of thoracoabdominal nerves exit through the fascial foramen 2, 3
- Pain is characteristically localized to a small area (often less than 2.5 cm in diameter) and can be reproduced with fingertip palpation 3, 4
- A diagnostic injection of 1% lidocaine into the trigger point that produces at least 50% pain reduction on visual analog scale confirms the diagnosis 4
Clinical Context and Pitfalls
- ACNES is commonly underdiagnosed despite affecting an estimated 13%-30% of adults with chronic abdominal pain, often leading to unnecessary invasive diagnostic evaluations 5, 2
- The syndrome is characterized by chronic abdominal pain caused by entrapment of cutaneous nerve branches, typically presenting as severe, often refractory pain 3
- Failure to examine for Carnett's sign can result in missed diagnosis and inappropriate workup for intra-abdominal pathology 1
- The diagnostic injection serves dual purposes: confirming the diagnosis when positive (>50% pain reduction) and providing initial therapeutic benefit 4
Treatment-Based Diagnostic Approach
- After identifying a positive Carnett's sign and trigger point, sequential diagnostic injections can help map the full extent of nerve involvement and identify referred pain patterns 5
- This treatment-based assessment allows the diagnosis to evolve clinically, demonstrating pathologic relationships between skeletal structures and myofascial tissues contributing to nerve irritation 5