Carpal tunnel syndrome is a hand and arm condition that causes numbness, tingling, and other symptoms. Carpal tunnel syndrome is caused by a pinched nerve in the wrist.
Numerous factors can contribute to carpal tunnel syndrome, including the anatomy of the patient's wrist, certain underlying health problems and possibly patterns of hand use.
Bound by bones and ligaments, the carpal tunnel is a narrow passageway located on the palm side of the patient's wrist. This tunnel protects the main nerve to the patient's hand and the nine tendons that bend his fingers.
Compression of the nerve produces the numbness, tingling and, eventually, hand weakness that characterize carpal tunnel syndrome.
Fortunately, for most people who develop carpal tunnel syndrome, proper treatment usually can relieve the tingling and numbness and restore wrist and hand function.
Carpal tunnel syndrome usually starts gradually with numbness or tingling in the patient's thumb, index and middle fingers that comes and goes. This may be associated with discomfort in the patient's wrist and hand. Common carpal tunnel syndrome symptoms include:
- Tingling or numbness. The patient may experience tingling and numbness in his fingers or hand, especially the thumb and index, middle or ring fingers, but not the little finger. This sensation often occurs while holding a steering wheel, phone or newspaper or, commonly, waking him from sleeping. The sensation may extend from the patient's wrist to his arm.
Many people "shake out" their hands to try to relieve their symptoms. As the disorder progresses, the numb feeling may become constant.
- Weakness. The patient may experience weakness in his hand and a tendency to drop objects. This may be due to the numbness in the patient's hand or weakness of the thumb's pinching muscles, which are controlled by the median nerve.
What are the causes of Carpal tunnel syndrome?
Carpal tunnel syndrome occurs as a result of compression of the median nerve.
The median nerve runs from the patient's forearm through a passageway in his wrist (carpal tunnel) to his hand. It provides sensation to the palm side of the patient's thumb and fingers, with the exception of the little finger. It also provides nerve signals to move the muscles around the base of your thumb (motor function).
In general, anything that crowds, irritates or compresses the median nerve in the carpal tunnel space can lead to carpal tunnel syndrome. For example, a wrist fracture can narrow the carpal tunnel and irritate the nerve, as can the swelling and inflammation resulting from rheumatoid arthritis.
In many cases, no single cause can be identified. It may be that a combination of risk factors contributes to the development of the condition.
What are the risk factors associated with Carpal tunnel syndrome?
A number of factors have been associated with carpal tunnel syndrome. Although by themselves they don't cause carpal tunnel syndrome, they may increase the patient's chances of developing or aggravating median nerve damage. These include:
- Anatomic factors. A wrist fracture or dislocation that alters the space within the carpal tunnel can create extraneous pressure on the median nerve.
People with smaller carpal tunnels may be more likely to have carpal tunnel syndrome.
- Sex. Carpal tunnel syndrome is generally more common in women. This may be because the carpal tunnel area is relatively smaller than in men, and there may be less room for error.
Women who have carpal tunnel syndrome may also have smaller carpal tunnels than women who don't have the condition.
- Nerve-damaging conditions. Some chronic illnesses, such as diabetes, increase your risk of nerve damage, including damage to your median nerve.
- Inflammatory conditions. Illnesses that are characterized by inflammation, such as rheumatoid arthritis, can affect the tendons in your wrist, exerting pressure on your median nerve.
- Alterations in the balance of body fluids. Fluid retention, common during pregnancy or menopause, may increase the pressure within your carpal tunnel, irritating the median nerve. Carpal tunnel syndrome associated with pregnancy generally resolves on its own after pregnancy.
- Other medical conditions. Certain conditions, such as menopause, obesity, thyroid disorders and kidney failure, may increase your chances of carpal tunnel syndrome.
- Workplace factors. It's possible that working with vibrating tools or on an assembly line that requires prolonged or repetitive flexing of the wrist may create harmful pressure on the median nerve or worsen existing nerve damage.
However, the scientific evidence is conflicting, and these factors haven't been established as direct causes of carpal tunnel syndrome.
Several studies have evaluated whether there is an association between computer use and carpal tunnel syndrome. However, there has not been enough quality and consistent evidence to support extensive computer use as a risk factor for carpal tunnel syndrome, although it may cause a different form of hand pain.