Carnett's Sign - Differential Diagnosis

Differential Diagnosis

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.

All abdominal wall hernias may be associated with pain and Carnett's test may be useful in their evaluation. The hernias of the anterior abdominal wall include: epigastric hernias, umbilical hernias, spigelian hernias and incisional hernias. Those of the groin include: direct inguinal hernia, indirect inguinal hernia, femoral hernia and sports hernia. Those of the pelvic wall include: sciatic hernia, obturator hernia and perineal hernia. The support hernias include: vault prolapse, enterocele, cystocele, rectocele and uterine decensus. Although most hernias can be detected clinically with the presence of a lump with an expansile cough impulse some may be difficult to detect either because they are small or because the patient is obese. In cases where the diagnosis is suspected but clinically unconfirmed, additional investigation using radiography or ultrasonography may be helpful. Herniography, in which contrast medium is introduced into the peritoneal cavity, has been successfully used to reveal previously unsuspected inguinal hernias in patients with groin pain of uncertain origin and to detect impalpable interparietal lesions such as Spigelian hernias.

Rib tip syndrome is characterized by pain along the costal margin and is caused by hypermobility of the eighth, ninth and tenth ribs. These ribs do not articulate with the sternum but instead are bound to each other by a thin band of fibrous tissue. If this fibrous attachment becomes divided, the rib(s) may ride up and irritate the intercostal nerve(s) causing pain. Clinically the patient may be aware of a snapping or clicking sensation as the ribs move relative to one another. The clinician can reproduce the symptoms by hooking his or her fingers under the costal margin and pulling upwards. Relief can be provided by anesthetizing the relevant intercostal nerve with local anesthetic. If symptoms persist, rib tip resection may be necessary.

Spontaneous rectus sheath hematoma arises from rupture of the epigastric vessels. The patient usually presents with a sudden well-localized abdominal pain associated with a tender nonpulsatile abdominal mass, usually in the lower abdomen. There is frequently a plausible precipitating factor such as local trauma, a bout of coughing or anticoagulant therapy. The diagnosis can be confirmed on ultrasound examination and a conservative approach to treatment can be adopted provided that the hematoma does not enlarge. Carnett's test may be diagnostic in this setting.