Carpal tunnel syndrome occurs when a nerve in the hand and forearm, known as the median nerve, gets pinched (compressed) within a passage called the carpal tunnel. The carpal tunnel is a narrow canal at the wrist through which the median nerve extends from the forearm to the hand and the first four fingers. It is surrounded by the wrist bones and , which are tissues that support the body’s joints and organs.
Carpal tunnel syndrome is often described as idiopathic because its cause is frequently unknown but can be influenced by lifestyle factors. Little is known about the genetic contributions to this condition. Most of the genes that have been studied provide instructions for making proteins that are components of connective tissues. Other genes associated with the condition play roles in nerve cell function, the immune system, or metabolism. Additionally, the width of the carpal tunnel varies among individuals; people with narrower passages are more likely to have nerve compression than are people with wider passages.
In carpal tunnel syndrome, nerve compression can be caused by many factors including inflammation of connective tissues surrounding the carpal tunnel, accumulation of fluids (edema) in the lower arm, hormonal changes, stress and trauma to the wrist, or obstructions within the carpal tunnel, such as a cyst or tumor. Carpal tunnel syndrome occurs in 20 to 45 percent of pregnant women, likely due to edema or hormonal changes, and often goes away at the end of the pregnancy.
Particular activities, often related to certain occupations, may increase a person’s risk of developing carpal tunnel syndrome. Repeated use of tools that vibrate or require forceful movements can put stress on the wrist, causing swelling or inflammation around the carpal tunnel. Whether repeated tensing of the hand and wrist, caused by frequent computer use, increases the risk of carpal tunnel syndrome is unclear; the evidence is conflicting. It is likely that the impact of computer use on the development of carpal tunnel syndrome is minor.
While carpal tunnel syndrome can be a feature of many disorders, including obesity, alcohol use disorder, rheumatoid arthritis, type 1 diabetes, type 2 diabetes, hypothyroidism, kidney (renal) failure, transthyretin amyloidosis, and hereditary neuropathy with liability to pressure palsies, it usually occurs in people with no related health conditions.