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Tinel's sign is a physical exam finding that can help point to the diagnosis of carpal tunnel syndrome. A positive sign can be elicited by tapping on the wrist over the region where the median nerve is located. Patients with carpal tunnel's syndrome will typically experience tingling and numbness in their middle fingers, index fingers, and thumbs as a result of tapping in this region. Although having a positive Tinel's sign can suggest the presence of carpal tunnel syndrome, this diagnosis is best confirmed by performing nerve conduction studies.
In order to understand why Tinel's sign is associated with carpal tunnel syndrome, it helps to understand why the syndrome develops. Part of the motor and sensory function of the hand is supplied by the median nerve. Since the nerve must pass through a narrow opening — the carpal tunnel — in the area of the wrist, it can often become compressed. When the nerve is compressed in this region, carpal tunnel syndrome results, causing symptoms including numbness or tingling of the fingers, pain in the fingers, poor coordination of the muscles of the hand, and weakness of the fingers. Typically the symptoms affect the middle finger, index finger, and thumb, as well as the half of the palm located near those fingers.
Patients who complain about symptoms associated with carpal tunnel syndrome are often thoroughly examined by physicians in order to see if they truly are affected by this condition. One of the physical exam tests that can be done to check for the syndrome is Tinel's sign. To perform this physical exam maneuver, a doctor or other health care professional taps the skin overlying the carpal tunnel, which is found in the middle of the wrist, right under the palm. When patients experience numbness and tingling in the hand as a result of this tapping, this is considered a positive result.
Having a positive Tinel's sign does not necessarily mean that a patient has carpal tunnel syndrome, as other conditions can also cause patient to have a positive result, such as problems causing compression of the median nerve at other locations. Patients with a condition called thoracic outlet syndrome, in which the origin of the median nerve is compressed at the level of the lower neck or upper arm, can also have a positive result. Generally, however, about three quarters of patients with a positive test result will have the syndrome.
Overall, Tinel's sign is not the best method for diagnosing carpal tunnel syndrome, as only approximately half of patients suffering from carpal tunnel syndrome will have a positive test. Other physical exam tests, such as the Phalen's sign, can be checked. The confirmatory test, however, is performing nerve conduction studies. In this test, needles are inserted into points along the path of the median nerve, and the speed with which electrical activity is conducted through the nerve is measured. Abnormal conduction results confirm the diagnosis of carpal tunnel syndrome.