Repetitive stress injuries
Biological Causes. Carpal tunnel syndrome is considered an inflammatory disorder caused by repetitive stress, physical injury, or a medical condition. It is often very difficult, however, to determine the precise cause of carpal tunnel syndrome. No tests are available to identify a specific cause. Except in patients with certain underlying diseases, the biological mechanisms leading to carpal tunnel syndrome are unknown.
Working Conditions versus Medical Problems. Although some studies suggest that more than half of CTS cases are associated with workplace factors, there is no strong evidence of a cause and effect relationship. In fact, most studies now strongly suggest that carpal tunnel syndrome is primarily associated with medical or physical conditions such as diabetes, osteoarthritis, hypothyroidism, and rheumatoid arthritis. CTS also tends to occur in people with certain genetic or environmental risk factors. These risk factors include obesity, smoking, alcohol abuse, or significant mental stress. CTS sometimes has a familial risk, implying some type of genetic origin. When such susceptible people are subjected to repetitive hand or wrist work, the risk for CTS can become significant. CTS, then, is very likely to be due to a combination of factors that lead to nerve damage in the hand.
High Force and Vibration. Even though medical and physical conditions may be the initial culprits leading to CTS, certain working conditions are especially related to nerve damage -- if not to pure cases of CTS. Work that involves high force or vibration is particularly hazardous, as is repetitive hand and wrist work in cold temperatures.
In addition to CTS, other disorders of the hand and wrist result from these work-related movements. They include the following:
All of these problems are generally associated with repetitive and forceful use of the hands, resulting in damaged muscles and bones of the upper arms.
A number of medical conditions increase the risk for or even cause CTS. The main conditions associated with CTS are diabetes, hypothyroidism, rheumatoid arthritis, osteoarthritis, obesity, and pregnancy. Many of the underlying diseases that contribute to the development of CTS are also associated with more severe forms of CTS.
Diabetes. CTS is a very common feature of diabetic neuropathy, one of the major complications of diabetes. Neuropathy is decreased or distorted nerve function; it particularly affects sensation. Symptoms include numbness, tingling, weakness, and burning sensations, usually starting in the fingers and toes and moving up to the arms and legs. About 6% of patients with CTS have diabetes. Up to 85% of patients with type 1 diabetes develop CTS. Development of CTS symptoms is related to the patient's age, and the length of time they had diabetes.
Autoimmune Diseases. In autoimmune diseases, the body's immune system abnormally attacks its own tissue, causing widespread inflammation, which, in many cases, affects the carpal tunnel of the hand. Such autoimmune diseases include rheumatoid arthritis, systemic lupus erythematosus, and thyroiditis, which can lead to hypothyroidism.. Some experts believe that CTS may actually be one of the first symptoms in a number of these diseases. Studies also suggest that CTS patients with these disorders are more likely to have severe CTS that requires surgery.
Diseases that Affect Muscle and Bones. Arthritis, gout, and other medical conditions that damage the muscles, joints, or bones in the hand may cause changes that lead to CTS.
Structural Abnormalities. Inborn abnormalities in the bones of the hand, wrist, or forearm may contribute to CTS.
Chronic Kidney Insufficiency. People who undergo hemodialysis for chronic kidney damage often experience a build-up of a certain type of protein, called beta 2-microglobulin, in the hand. This build-up can result in CTS. The longer the person has been receiving hemodialysis, the greater the risk of CTS. Certain drugs and procedures (particularly one procedure called hemodiafiltration) are being investigated as having the potential to reduce microglobulin build-up. It is hoped such new methods will delay the need for carpal tunnel surgery in patients undergoing long-term hemodialysis.
Other Diseases. A number of other medical conditions may cause or increase susceptibility to CTS:
Medications. According to case reports, a number of medications may increase the risk for temporary CTS. They include certain medications that affect the immune system (such as interleukin-2), and anticlotting drugs (such as warfarin). There has been conflicting evidence as to whether corticosteroids and hormone replacement therapy may increase the risk of CTS. More research is needed before a cause-and-effect association can be established.
Bone dislocations and fractures can narrow the carpal tunnel, thereby exerting pressure on the median nerve.
Hormonal fluctuations in women play a role in CTS. Such fluctuations may cause fluid retention and other changes that cause swelling in the body. Fluid retention is one reason that CTS may develop during pregnancy.
CTS is associated with a family history of the disorder. Many of these cases can be the result of physical characteristics or medical conditions associated with CTS, which also run in families. However, in one study, 17% of family clusters of CTS were not associated with any such medical conditions, suggesting the genetic factors may be important in some people. Carpal tunnel syndrome in young people most likely has a genetic component.
Other genetic factors that may contribute to this disorder include abnormalities in certain genes that regulate myelin, a fatty substance that serves as insulation for nerve fibers.
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