Carnett's sign

In medicine, Carnett's sign is a finding on clinical examination in which (acute) abdominal pain remains unchanged or increases when the muscles of the abdominal wall are tensed. For this part of the abdominal examination, the patient can be asked to lift the head and shoulders from the examination table to tense the abdominal muscles. An alternative is to ask the patient to raise both legs with straight knees.

A positive test increases the likelihood that the abdominal wall and not the abdominal cavity is the source of the pain (for example, due to rectus sheath hematoma instead of appendicitis). A negative Carnett's sign is said to occur when the abdominal pain decreases when the patient is asked to lift the head; this points to an intra-abdominal cause of the pain.

This test was first described by John B. Carnett in 1926. The first clear description of anterior abdominal wall pain arising from structures other than the underlying viscera was Cyriax in 1919. Cyriax considered that pain could be mimicked by lesions that arose from the vertebra, ribs or other associated structure or that they were the result of direct irritation of intercostal nerves. By identifying conditions such as alterations in the normal vertebral curves, minor subluxation of vertebral bodies and pressure on the peripheral portions of the intercostal nerves, he was able to employ various mechanical treatments to correct the abnormalities and relieve his patients’ symptoms. Despite this paper little attention was paid to this problem until Carnett developed his simple clinical test. Carnett thought that lower abdominal pain was commonly caused by the lower six thoracic nerves and wanted to be able to distinguish this origin from that arising from the viscera.

The differential diagnosis of a positive Carnett's test includes hernias, nerve entrapment syndrome, irritation of intercostal nerve roots, anterior cutaneous nerve entrapment, rib-tip syndrome, myofascial pain, trigger points and rectus sheath hematomas.

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