Why is Tinel's sign positive in carpal tunnel syndrome (CTS)?

From the Guidelines

Tinel's sign is positive in carpal tunnel syndrome (CTS) because the compressed median nerve at the wrist is irritated, leading to increased sensitivity and abnormal action potentials when tapped, as supported by the latest clinical guidelines and studies, including the 2023 update on chronic hand and wrist pain 1. The diagnosis of CTS can be confirmed using various methods, including clinical assessment, electrophysiologic studies, and ultrasound (US) evaluation of the median nerve, with US being highly sensitive and specific for CTS diagnosis 1. To understand the positivity of Tinel's sign in CTS, it is essential to consider the following key points:

• The compressed median nerve becomes more sensitive to mechanical stimulation, leading to abnormal action potentials when tapped.
• The brain interprets these abnormal action potentials as tingling or shock-like sensations in the nerve's distribution area, which includes the thumb, index, middle, and half of the ring finger.
• Tinel's sign is not specific to CTS and can be positive in other nerve compression syndromes, emphasizing the need for a comprehensive clinical evaluation and patient history for accurate diagnosis. The performance of Tinel's test involves:

1. Having the patient's wrist slightly extended.
2. Tapping firmly over the median nerve at the wrist crease.
3. A positive result is when the patient reports tingling or electric shock sensations in the thumb, index, middle, and half of the ring finger. It is crucial to note that while Tinel's sign can be a useful diagnostic tool, its accuracy and reliability can be influenced by various factors, including the examiner's technique and the patient's overall clinical presentation, as highlighted in recent studies on chronic hand and wrist pain 1.

From the Research

Tinel's Sign in Carpal Tunnel Syndrome

Tinel's sign is a clinical test used to diagnose carpal tunnel syndrome (CTS). The test involves lightly tapping the median nerve along its course in the wrist to elicit a tingling sensation in the distribution of the nerve. A positive Tinel's sign is often indicative of median nerve compression or irritation.

Mechanism of Tinel's Sign

• The mechanism of Tinel's sign is thought to be related to the increased sensitivity of the median nerve's compressed fibers in the carpal tunnel 2.
• The test is based on the principle that lightly tapping the nerve will cause a tingling sensation in the areas innervated by the nerve, indicating nerve compression or irritation.

Correlation with Nerve Conduction Studies

• Studies have shown that Tinel's sign correlates with abnormal nerve conduction studies, particularly with distal motor and sensory latency 2.
• A positive Tinel's sign has been found to be associated with a higher frequency of abnormal nerve conduction studies, indicating median nerve compression 2.

Diagnostic Accuracy

• The sensitivity and specificity of Tinel's sign in diagnosing CTS have been reported to be variable, ranging from 30-46% sensitivity and 51-97% specificity 3, 4.
• The combination of Tinel's sign and Phalen's test has been found to improve diagnostic accuracy in CTS 4.

Clinical Implications

• A positive Tinel's sign is often used as an indicator of median nerve compression or irritation, and can be used to guide treatment decisions in CTS 5, 6.
• The test is a useful adjunct to other diagnostic tests, such as nerve conduction studies and electromyography, in confirming a diagnosis of CTS 3, 4.