Carpal tunnel syndrome arises from pressure on the median nerve, which runs through a narrow passageway in the wrist called the carpal tunnel. This compression can lead to numbness, tingling, weakness, or pain, primarily affecting the thumb, index, middle, and part of the ring finger. While these symptoms are strong indicators, they are not enough for a definitive conclusion. To accurately diagnose the condition and rule out other potential causes, physicians use a structured evaluation involving several types of medical tests to identify the root cause before treatment begins.
In-Office Physical Examinations
The diagnostic journey begins with a physical examination where a doctor evaluates the hand and wrist. This step involves a discussion of symptoms and a visual inspection for any signs of muscle atrophy at the base of the thumb, which can occur in advanced stages. Clinicians then perform a series of provocative maneuvers designed to reproduce the symptoms of carpal tunnel syndrome.
One of the most common tests is the Phalen’s maneuver. The patient is asked to press the backs of their hands together with fingers pointing downward, holding the wrists in maximum flexion for up to a minute. This position increases pressure within the carpal tunnel, and if it elicits tingling or numbness in the fingers, it suggests compression of the median nerve.
Another frequently used technique is Tinel’s sign, where the physician gently taps over the median nerve at the wrist. A positive test results in a tingling sensation or a feeling akin to a mild electric shock in the fingers. A third procedure is the carpal compression test, also known as Durkan’s test, where an examiner applies firm pressure over the carpal tunnel for about 30 seconds. The onset of pain or numbness during this compression points toward carpal tunnel syndrome.
Electrodiagnostic Testing
To obtain a more conclusive diagnosis, physicians use electrodiagnostic testing, which directly assesses the function of the median nerve. These studies provide objective data on how well electrical signals are transmitted, helping to confirm the presence and severity of nerve compression. They are particularly useful when physical exam findings are ambiguous or when considering surgery.
The primary test used is the nerve conduction study (NCS). During an NCS, small electrodes are placed on the skin over the median nerve at different points. A mild electrical impulse is sent through one electrode to stimulate the nerve, and the other electrodes record the time it takes for the signal to travel between them. A noticeable slowing of the impulse as it crosses the wrist is a strong indication of compression within the carpal tunnel.
An electromyography (EMG) is sometimes performed with an NCS to provide a more complete picture. This test evaluates the health of the muscles that receive signals from the median nerve. It involves inserting a thin needle electrode into specific muscles to measure their electrical activity. Abnormal electrical patterns can reveal if nerve compression has caused muscle damage, and an EMG is also effective at ruling out other conditions, such as a pinched nerve in the neck.
Diagnostic Imaging
In some cases, a physician may order diagnostic imaging to visualize the anatomical structures within the wrist. Unlike electrodiagnostic tests that measure nerve function, imaging provides a direct view of the median nerve and its surroundings. This can help identify the physical cause of the nerve compression and exclude other pathologies that might mimic the symptoms.
Musculoskeletal ultrasound is a commonly used imaging tool for this purpose. It uses high-frequency sound waves to generate a real-time image of the carpal tunnel. A clinician can use ultrasound to see if the median nerve appears swollen or flattened, which are direct signs of compression. The technology allows for precise measurement of the nerve’s cross-sectional area, and an enlarged area at the wrist is an indicator of the condition.
Magnetic Resonance Imaging (MRI) is another imaging option, though it is used less frequently for diagnosing carpal tunnel syndrome. An MRI provides highly detailed images of the wrist’s soft tissues and bones. Its main utility is to rule out other problems that could be causing the symptoms, such as a tumor, cyst, or complications from arthritis. It is reserved for cases where the diagnosis remains unclear after other forms of testing.