The carpal tunnel is a passageway through the wrist that protects the nerves and tendons that extend into the hand. The median nerve within the carpal tunnel is in close proximity to nine tendons. When the tissues that constitute the tunnel become inflamed or swollen, or if one or more of the tendons becomes injured, the median nerve is compressed. This compression of the median nerve within the carpal tunnel produces paresthesia in the thumb and the second, third and radial half of the fourth fingers as well as, in some cases, atrophy of thenar musculature.(1)
Entrapment of the nerve at the wrist may be secondary to excessive use of the wrist, tenosynovitis with arthritis, or local infiltration, for example, by a thickening of connective tissue as in acromegaly, by deposit of amyloid, or by one of the mucopolysaccharidoses.(2) The development of carpal tunnel syndrome may also be secondary to other diseases such as diabetes mellitus, rheumatoid arthritis, and hypothyroidism. However, patients with carpal tunnel syndrome secondary to these diseases represent a very small percentage of total cases. It also may occur during pregnancy as a result of weight gain and fluid retention, and may additionally be associated with edema or trauma.(3)
Diagnosis is suggested when the physician finds a positive Phalen's sign (pressing the extensor surface of the two flexed wrists against each other causing paresthesia) or Tinel's sign (thumping of the volar aspect of the wrist to see if paresthia is induced).