Carpal tunnel syndrome may be written into your wrists at birth
Carpal tunnel syndrome is often blamed on typing or repetitive work, and those strains do count as risk factors. But genes appear to be the biggest factor: one large genetic study found 50 regions of DNA linked to the condition, several of them already known for influencing how tall people grow.
The carpal tunnel is a narrow passage at the base of the palm, walled on three sides by an arch of wrist bones and roofed by a tough band called the transverse carpal ligament. Nine flexor tendons squeeze through it alongside the median nerve, which carries feeling from the thumb, index and middle fingers and half the ring finger, and works the muscles that swing the thumb away from the palm. Anything that raises pressure inside that space can compress the nerve.
What happens next follows a dose-response pattern: more pressure for longer means more damage. First the barrier protecting the nerve's blood supply leaks. Continued squeezing strips the nerve's insulating myelin, so signals travel abnormally even after the pressure eases, until it regrows. Severe compression can injure the axons themselves, bringing weakness and wasting of the muscles at the base of the thumb. Most patients have the mildest grade of injury, a conduction block from which the nerve can fully recover. Lab work shows why bent wrists matter: flexing or extending the joint can push tunnel pressure as high as 111 mm Hg, while people with the syndrome tend to sit at 12 to 31 mm Hg against 2.5 to 13 in controls.
The telltale symptoms are numbness, tingling or burning in those fingers, typically worst at night because many people sleep with their wrists curled. The palm itself usually keeps normal feeling, since the branch serving it leaves the nerve before the tunnel. Researchers estimate about one person in ten is affected at some point, making it the commonest nerve compression syndrome, though figures vary with how cases are defined.
Most cases have no identifiable cause. Associated factors include vibration and forceful or repetitive hand use at work, being female, obesity, diabetes, rheumatoid arthritis and thyroid disease. Evidence that steroid injections beat placebo is mixed, and surgery to divide the transverse carpal ligament is the only treatment known to change the course of the disease.
Source: Carpal tunnel syndrome
