Carnett’s sign

Carnett’s test is a simple clinical test in which abdominal tenderness is evaluated while the patient tenses the abdominal muscles. Carnett’s test is useful for differentiating abdominal wall pain from intra-abdominal pain. Carnett sign, first described in the 1920s ¹, a positive Carnett’s sign if there is an exacerbation of the pain with flexion of the abdominal wall muscles. The presence of the Carnett sign strongly supports the diagnosis of abdominal wall pain.

The Carnett test is performed by palpating the abdomen of the supine patient in the usual way to elicit the area of tenderness. When the tender spot is localized, the patient is asked to contract the abdominal muscles by raising the head and trunk or lower extremities off the examining table while the examiner continues to hold pressure. Once the muscles are tensed, the patient is asked if the pain has altered. A Carnett sign consists of stable or worsening pain at the point of maximal tenderness during contraction of the abdominal wall musculature ². If the cause of symptoms is intra-abdominal, the tensed muscles protect the viscera and the tenderness diminishes. In contrast, if the pain originates in the abdominal wall, the tenderness increases or remains unchanged, known as the Carnett sign or positive Carnett’s sign ³. This indicates the origin of the pain likely is the abdominal wall rather than an intra-abdominal source. Tenderness originating from inside the abdominal cavity usually decreases when a supine patient tenses the abdominal wall by lifting head and shoulders off the examining table ⁴. In acute abdominal pain, Carnett’s sign has been established as a simple but useful physical examination for differential diagnosis. A positive Carnett’s sign suggests likely abdominal wall pain and a negative sign suggests likely visceral pain.

Pain relief after injection of a local anesthetic is considered confirmation of the diagnosis of abdominal wall pain ⁵, with Sharpstone and Colin-Jones ⁶ concluding that a successful injection after elicitation of the Carnett sign (to diagnose abdominal wall pain) is “one of the most cost effective procedures in gastroenterology.” Although the Carnett test alone is 78% sensitive and 88% specific for diagnosing abdominal wall pain ⁵, it is important to note that there can be a high placebo effect with injections ⁷ and the presence of abdominal wall pain does not always rule out an existing intra-abdominal source of pain. Studies have revealed an intra-abdominal source of pain in 3% to 9% patients with abdominal wall pain diagnosed by the presence of a Carnett sign, with the most common cause being appendicitis ⁸. In many of the cases in which a visceral source of pain was subsequently diagnosed, warning signs such as unintentional weight loss were present. Therefore, like any other sign, the presence of a Carnett sign should be interpreted in context, and the clinician should remain alert to warning symptoms or signs. Furthermore, abdominal wall pain can coexist with irritable bowel syndrome and other functional gastrointestinal disorders ⁹, which may complicate the clinical presentation.

References

1. Carnett, J.B. Chronic pseudoappendicitis due to intercostal neuralgia. Am J Med Sci. 1927; 174: 579–599
2. Longstreth, G.F. Carnett’s legacy: raising legs and raising awareness of an often misdiagnosed syndrome. Dig Dis Sci. 2016; 61: 337–339
3. Thomson H, Francis DM. Abdominal-wall tenderness: a useful sign in the acute abdomen. Lancet. 1977;2(8047):1053–4.
4. Greenbaum DS, Greenbaum RB, Joseph JG, Natale JE. Chronic abdominal wall pain. Diagnostic validity and costs. Dig Dis Sci. 1994;39:1935–41.
5. Srinivasan, R. and Greenbaum, D.S. Chronic abdominal wall pain: a frequently overlooked problem. Am J Gastroenterol. 2002; 97: 824–830
6. Sharpstone, D. and Colin-Jones, D.G. Chronic, non-visceral abdominal pain. Gut. 1994; 35: 833–836
7. Straus, J.L. and von Ammon Cavanaugh, S. Placebo effects: issues for clinical practice in psychiatry and medicine. Psychosomatics. 1996; 37: 315–326
8. Costanza, C.D., Longstreth, G.F., and Liu, A.L. Chronic abdominal wall pain: clinical features, health care costs, and long-term outcome. Clin Gastroenterol Hepatol. 2004; 2: 395–399
9. van Assen, T., Boelens, O.B., Kamphuis, J.T., Scheltinga, M.R., and Roumen, R.M. Construction and validation of a questionaire distinguishing a chronic abdominal wall pain syndrome from irritable bowel syndrome. Frontline Gastroenterol. 2012; 3: 288–294