Diagnosis of carpal tunnel syndrome is based on the history of symptoms, presence of risk factors, physical and neurological examination, and diagnostic tests.
Neurological examinations test the three thenar muscles that abduct, flex and oppose the thumb (the abductor pollicis brevis, flexor pollicis brevis and opponens pollicis respectively).
Following this there are three main tests designed to reproduce symptoms. Look for wasting in the median nerve distribution, and loss of motor (thenar muscle strength: weak thumb abduction) and sensory function.
Tinel’s Sign – Holding the wrist in extension and tapping the palm sharply causing tingling sensation.
Phalen’s Maneuver – Hold the wrist in passive wrist flexion for roughly 60 seconds.
Durkan Test – Examiner presses thumb over carpal tunnel, holding pressure for around 30 seconds.
The Durkan test is the most reliable of the three, having proven to be accurate 90% of the time in Durkan’s study. Tinel’s sign is the least reliable with negative diagnoses in up to 30% of patients with electrophysiologically proven median nerve compression. Phalen’s test has a false negative rate of postive LR 1.3, negative LR 0.7).
Other conditions may also be misdiagnosed as carpal tunnel syndrome including inflammation (radiculopathy) of nerve roots C6 and C7 in the cervical spine and compression of the median nerve outside the carpal tunnel. Thus, if, based on history and physical examination, a CTS diagnosis is suspected but not clear, patients will likely be tested electrodiagnostically with nerve conduction studies and electromyography; MRI or ultrasound imaging are also used.
Electro Diagnosis
Nerve conduction velocity (NCV) and electromyography (EMG) are used to evaluate nerve and muscle function.
NCV involves placing electrodes on the skin above the median nerve to monitor the speed at which an impulse travels along the nerve.
In essence, NCV uses deploys electrodes at different parts of the skin over the nerve, where one electrode stimulates and the others monitor the subsequent electrical activity. The time for the electrical impulse to travel and the distance between the electrodes is used to calculate the speed. Slowing across the wrist for the motor and sensory latencies of the median nerve indicates focal compression of the median nerve at the wrist.
An EMG detects the electrical potential generated by muscle cells when these cells contract, and also when the cells are at rest. For CTS, EMG involves placing small electrodes in the form of a needle into the abductor pollicis brevis muscle to detect abnormalities that may indicate that the median nerve supplying the muscle is damaged.
The EMG is often performed simultaneously with the NCV, and thus the two are often referred to together as EMG/NCV studies.
http://www.medterms.com/script/main/art.asp?articlekey=34030
http://www.arthritis-treatment-and-relief.com/nerve-conduction-test-carpal-tunnel-syndrome.html
http://www.neurohaven.com/emg1.htm
http://www.fpnotebook.com/Ortho/Exam/CrplCmprsnTst.htm
http://www.ejbjs.org/cgi/content/abstract/73/4/535
http://www.neurologychannel.com/carpaltunnel/diagnosis.shtml
http://www.ninds.nih.gov/disorders/carpal_tunnel/detail_carpal_tunnel.htm
No comments:
Post a Comment