Carpal Tunnel Syndrome Diagnosis
History: Individuals may describe pain, tingling, numbness, or a feeling of weakness in the wrist, hand, or fingers. In mild cases, the symptoms are intermittent and often worsen at night or when the individual first arises in the morning. The individual may complain of decreased grip strength, dropping items more frequently than usual, and having problems pinching or grasping items or making a fist. The fingers may at times feel "locked," and the individual may feel a need to shake the hand and fingers to unlock them. On occasion, pain may radiate into the forearm, shoulder, neck, or chest. The hands or lower arms may feel weak in the morning after sleeping with wrists flexed. Performance of detailed tasks such as writing or tying shoes may be difficult. Symptoms may occur during specific activities or at particular times, such as while holding a phone or a newspaper, gripping a steering wheel, or sleeping. The individual may not be sensitive to hot and cold by touch.
Physical exam: The physical exam may reveal no abnormalities. Subjectively altered sensation may be noted in the distribution of the median nerve in the thumb and the first three fingers, with no changes in sensation in the palm. Even though patients frequently complain of "swelling," soft tissue swelling is not usually observed in CTS. In chronic or severe cases, the palm may appear to be wasting away near the thumb (thenar eminence atrophy). In severe cases, weakness of thumb opposition and decreased sensation in the distal phalanges of the thumb and first three fingers (2 point discrimination and/or monofilament testing) may be noted. The individual may be shown a diagram of the hand and wrist to indicate where pain or other sensations are present. An unaffected little finger may indicate CTS.
Tapping on the volar aspect of the wrist over the course of the median nerve near the front of the wrist typically reproduces the tingling feeling in the hand or forearm (Tinel's sign). Positioning the wrist in a fully flexed posture for 60 seconds may reproduce the pain and tingling (Phalen's sign). These methods have a high rate of both false positive and false negative findings. Hand grip strength test may show weakness.
Tests: Electrodiagnostic nerve tests are performed to evaluate nerve function (e.g., nerve conduction velocity, electromyography). Nerve conduction tests apply small electric shocks and measure the speed with which nerves are able to transmit impulses. Mild cases may show prolonged motor and/or sensory distal latency of the median nerve and slowing of the conduction speed in the carpal tunnel. Moderate cases show conduction block, in which some of the axons or nerve fibers fail to transmit impulses, resulting in decreased amplitude (voltage) on nerve conduction. Severe cases, which are uncommon, show significant prolongation of motor latency and reduced conduction speed, evidence of axon loss or death of some of the axons in the nerve. There is no agreement about the definitions of mild, moderate, or severe CTS with regard to electrodiagnostic testing, but abnormal results on nerve conduction tests confirm CTS.
Electromyography involves insertion of a fine needle into a muscle and recording of the electric impulses so that electrical activity seen on a monitor can reveal damage to the nerve supplying the muscle tested. The most severe cases will show voltage or at least conduction block), suggesting more severe nerve injury.
Blood tests (serology) to detect possible underlying rheumatoid arthritis (sedimentation rate), diabetes, and thyroid disease are frequently performed. Plain film x-rays of the wrist are used to rule out bony abnormalities, but are almost always normal. MRI and ultrasound are currently considered to be experimental methods of evaluating for the presence of CTS. If a tumor in the carpal tunnel is a rare but possible explanation for an individual's carpal tunnel syndrome, MRI may be used.
