Carpal Tunnel Syndrome
DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of Carpal Tunnel Syndrome.
Alternative NamesRepetitive Stress Injuries; Thoracic Outlet Syndrome
Biologic Causes. Carpal tunnel syndrome (CTS) is considered an inflammatory disorder caused by repetitive stress, physical injury, or medical conditions.It is often very difficult, however, to determine the precise cause of carpal tunnel syndrome. No tests that can identify a specific cause are available. Except in patients with certain underlying diseases, the biologic mechanisms leading to carpal tunnel syndrome are unknown. Although an overactive immune response that causes inflammation and damage in the joints or muscles is responsible for a number of arthritic conditions, similar problems are not likely to play an important role in CTS. More likely, reduced blood flow and lack of oxygen are important in the process leading to progressive swelling and scarring.
Working Conditions versus Medical Problems. Although studies suggest that more than half of CTS cases are associated with workplace factors, there is no strong evidence of a causal 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. It generally tends to occur in such people with certain genetic or environmental risk factors, such as obesity, smoking, alcohol abuse, or significant mental stress. When such susceptible people are then subjected to repetitive hand or wrist work, the risk for CTS can become significant. Carpal tunnel syndrome, then, is very likely to be due to convergences of factors that lead to nerve damage in the hand.
Work-Related Issues and Carpal Tunnel Syndrome
Workmen's Compensation and CTS. The issues surrounding workmen's compensation are particularly troubling in determining accurately whether labor conditions cause CTS. Carpal tunnel syndrome is a major contributor to workmen's compensation cases, and the employer and employee have opposite motivations in placing the blame for CTS on the job.
High Force and Vibration. Still, even though medical and physical conditions may be the initial culprits leading to carpal tunnel syndrome, certain working conditions are significantly related to nerve damage--if not to pure cases of CTS. Work that involves repetitive hand and wrist work in cold temperatures, high force, and vibration is particularly hazardous.
In addition to carpal tunnel syndrome, other disorders of hand and wrist are attributed to these work-related movements. They include the following:
All of these problems are generally associated with repetitive and forceful use of the hands that damage muscles and bones of the upper extremities.
Incorrect Posture. Incorrect posture may also play a role in the development of CTS in people who work at a computer and other types of keyboards. The tendency to roll the shoulders forward, round the lower back, and thrust the chin forward can shorten the neck and shoulder muscles, compressing nerves in the neck. This, in turn, can affect the wrist, fingers, and hand. Evidence is not as strong for a causal relationship, because people with poor posture may also have physical abnormalities that increase the risk for CTS.
Psychosocial Factors in the Workplace. Studies indicate that psychosocial factors in the workplace, such as intense deadlines, a poor social work environment, and low levels of job satisfaction, are major contributors to carpal tunnel pain. Such psychosocial conditions are more likely to be important factors in contributing to CTS in office workers, although they also complicate the condition in workers whose work is primarily physical.
A number of medical conditions increase the risk for or even cause carpal tunnel syndrome. 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 carpal tunnel syndrome are also associated with more severe forms of CTS.
Diabetes. Carpal tunnel syndrome 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 carpal tunnel syndrome have diabetes.
Autoimmune Diseases. In autoimmune diseases, the body's immune system abnormally attacks its own tissue, causing widespread inflammation, including, in many cases, the carpal tunnel of the hand. Such autoimmune diseases include rheumatoid arthritis, systemic lupus erythematosus, and hypothyroidism. Some experts believe that carpal tunnel syndrome 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 require 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 carpal tunnel syndrome. In fact, in one 2000 study, susceptibility to muscle and bone diseases was the major risk factor for CTS in British women. Osteoporosis (loss of bone density), although not a direct cause of CTS, increases the risk for fractures of the wrist that can lead to CTS.
Injuries and Previous Surgeries. Injuries, fractures, and operations that affect the forearm, wrist, or hand may lead to CTS, sometimes many years after the event.
Structural Abnormalities. Inborn abnormalities in the bones of the hand, wrist, or forearm may contribute to carpal tunnel syndrome.
Chronic Kidney Insufficiency. People who undergo hemodialysis for chronic kidney damage (renal insufficiency) often experience a build-up in the hand of a certain type of protein called beta 2-microglobulin. This can result in CTS and the longer the duration of the hemodialysis the greater the risk. Certain drugs and procedures (particularly one called hemodiafiltration) are being investigated to reduce microglobulin build-up and 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 carpal tunnel syndrome:
Medications. According to case reports, a number of medications may possibly increase the risk for temporary carpal tunnel syndrome. 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 risk. More research is warranted before a causal association can be established.
Bone dislocations and fractures can narrow the carpal tunnel, thereby exerting pressure on the median nerve.
Obesity and Lack of Fitness
Being overweight consistently turns up as a risk factor for CTS and may play a direct causal role on CTS. Greater body mass appears to reduce nerve flow speed into the hand.Obesity is also related to poor physical fitness, which may also increase risk.
Hormonal fluctuations in women play a role in carpal tunnel syndrome. Such fluctuations may cause fluid retention and other changes in the body that cause swelling. Fluid retention is one reason that CTS may develop during pregnancy.
Carpal tunnel syndrome is strongly associated with a family history of the disorder. Many of these cases can be attributed to physical characteristics or medical conditions associated with CTS that also run in families. However, in one study 17% of family clusters of carpal tunnel syndrome were not associated with any such medical conditions, suggesting the genetic factors may be important in some people. Carpal tunnel that develops in young people is most likely to have a genetic component.
For example, a 2000 study suggested that some patients with CTS may have a genetic defect that produces higher levels of a certain collagen subtype. (Collagen is the protein that is used to build all connective tissue, muscle, bones, and ligament.) The collagen found in CTS patients tends to produce stiffness.
Other genetic defects that may contribute to this disorder include abnormalities in certain genes that regulate myelin, a fatty substance that serves as insulation for nerve fibers.