carpal tunnel syndrome
Median nerve entrapment at the wrist is the most common of all entrapment neuropathies. In nearly all patients, the usual site of compression occurs in the carpal tunnel and results in a constellation of symptoms and signs known as the carpal tunnel syndrome (CTS). Although CTS usually is bilateral, both clinically and electrically, the dominant hand generally is more severely affected. Patients complain of wrist and arm pain associated with paresthesia in the hand. Carpal tunnel syndrome (CTS) is very common. In the U.S., approximately 5% of the general population will suffer from the effects of carpal tunnel syndrome. Caucasians have the highest risk of being diagnosed with CTS compared with other races. Women suffer more from CTS than men with a ratio of 3:1 between the ages of 45–60 years of age.
It is important to emphasize that CTS is a clinical diagnosis. Although the reported causes of CTS are numerous, most cases are idiopathic. The pathophysiology of CTS typically is demyelination. The EMG/NCS evaluation of a patient suspected of having CTS is directed toward the following: (a) demonstrating focal slowing or conduction block of median nerve fibers across the carpal tunnel; (b) excluding median neuropathy in the region of the elbow; (c) excluding brachial plexopathy; and (d) excluding cervical radiculopathy.
There is a group of patients with clinical symptoms and signs of CTS in whom these routine studies are normal (approximately 10%-25% of CTS patients). In such patients, the electrodiagnosis of CTS will be missed unless further testing is performed using more sensitive nerve conduction studies. Those studies usually involve a comparison of the median nerve to another nerve in the hand. The diagnostic yield increases from approximately 75% using routine motor and sensory studies to approximately 95% using these more sensitive techniques.