Carpal tunnel syndrome (CTS) is one of the most common mononeuropathies. It typically occurs within the confines of the carpal tunnel in the wrist. The median nerve can also be entrapped in the forearm as a pronator or interosseous syndrome. The entrapment can be caused by anything that causes a decrease in the size of the carpal tunnel (e.g., Colles' fracture, rheumatoid arthritis, congenital carpal tunnel stenosis), enlargement of the median nerve (e.g., diabetes, amyloidosis, thyroid disease, neuroma), or an increase in the volume of other structures within the carpal tunnel (e.g., tenosynovitis, ganglion, gout, urate deposits, lipoma, hematoma, fluid retention in pregnancy).
Other risk factors include any tasks that require repeated or sustained stress over the base of the palm. Low-frequency vibration exposure is another well-recognized risk factor for CTS. Repetitive wrist and hand movements such as knitting, typing, painting, woodworking, and weightlifting are also implicated as high-risk factors.
Common symptoms include numbness and paresthesias in the sensory distribution of the median nerve (palmar surface of thumb, index finger, and middle finger; radial side of ring finger; radial two thirds of palm). The patient may also have pain at rest (especially at night), weakness in the thumb, and thenar atrophy. Signs include a positive Tinel's sign at the wrist (tingling in median nerve distribution on percussion over ventral wrist), positive Phalen's sign (similar findings within 45 seconds after placing patient's wrist in maximal flexion), pain or paresthesias in a median distribution with thumb pressure over the median nerve for up to 30 seconds, and thenar atrophy. CTS can present with many variations, including proximal pain in the arm and shoulder, and with normal EMG.
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