Aetiology
This syndrome is associated with a wide variety of potential epidemiological risk factors, including age between 40 and 60 years, high body mass index, pregnancy, and occupations involving repetitive movements of the wrist.
Variations in the anatomy of the carpal tunnel can also contribute to risk and might be inherited. Most notably, congenital carpal tunnel stenosis may predispose an individual (or family) to the development of carpal tunnel syndrome (CTS).[7][8] Beyond this, emerging research suggests that CTS and trigger finger, another entrapment condition affecting the hand that sometimes co-occurs with CTS, may share a common genetic risk locus.[9] The role of genetic predisposition in CTS, if any, has yet to be defined.
Ultimately, it is rare to find any single definite cause in a patient, and causation is very likely to be multi-factorial. It should be noted that in the CTS literature many studies fail to adequately control for even a small number of these potential confounders. This fact, together with the lack of any clear common diagnostic criteria, makes many of these studies difficult to interpret.[10]
Pathophysiology
The final common pathway for most of these potential risk factors is the development of raised pressure within the carpal tunnel and/or the median nerve segment that lies within the tunnel.[11] The increased pressure could trigger off a chain of negative events that ultimately leads to ischaemia and scarring of the nerve.[12] Ischaemia is likely to be the cause of the typical intermittent sensory symptoms of CTS (i.e., numbness and pain); if it remains intermittent, then no axonopathy occurs. Pressure on the nerve will also lead to demyelination (and ultimately axonal loss), which is the main finding on neurophysiological testing. Demyelination per se causes no symptoms to the patient, and this may explain in part the subgroup of individuals who have no symptoms of CTS but who have abnormalities on nerve conduction studies, and alternately the group who have symptoms but no abnormalities on neurophysiological tests.[13][14]
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