Carpal tunnel syndrome (CTS) is a condition in which the nerve that runs down the arm to the hand, called the median nerve, becomes compressed or entrapped at the wrist. The nerve swells and leads to numbness, tingling, aching, and weakness in the hand. In most people, the symptoms of carpal tunnel syndrome get worse over time. Weakness in the fingers and wrist may in fact become debilitating, impacting a person’s ability to complete simple, everyday tasks and activities.
What Causes Carpal Tunnel Syndrome?
The “carpal tunnel” is a narrow canal on the palm side of the hand, formed by the carpal bones on the bottom of the wrist and the transverse carpal ligament across the top of the wrist. The median nerve and adjacent tendons run from the forearm into the hand and control the thumb and first three fingers. Any factor that further constricts the already narrow passageway and squeezes the median nerve at the wrist can lead to the painful symptoms of carpal tunnel syndrome.
There appears to be no single cause of carpal tunnel syndrome. Instead, it is believed to be caused by a combination of risk factors. There are many conditions that increase the risk of swelling of the median nerve in the wrist that leads to the painful symptoms of CTS.
Specifically, these risk factors include the genetic predisposition a person may have to a narrower tunnel in the wrist, as well as any trauma or injury to the wrist that can cause swelling, or a cyst or tumor in the carpal passageway; in addition, inflammatory conditions such as arthritis can affect the lining around the tendons and create pressure on the median nerve. Other health conditions that cause fluid retention, like lymphedema and impaired kidney function, can compress the median nerve as well. Pregnancy and menopause are also associated with fluid retention. Individuals with metabolic disorders that affect the nerves, such as obesity and diabetes, also have a higher risk of carpal tunnel syndrome, as do people with an underactive thyroid.
People with these conditions who work with vibrating tools or in jobs that require prolonged stress on the wrist can exacerbate their risk for carpal tunnel syndrome. Ergonomics play a role, and poor positioning during typing, playing a musical instrument, or other such tasks may contribute to carpal tunnel syndrome.
Carpal tunnel syndrome used to be thought of largely as an overuse or repetitive motion injury, but doctors now recognize the role of genetics in the condition. Some individuals simply have smaller carpal passageways, and more prone wrist shape and thus may be genetically more predisposed to compression of the median nerve. In fact, CTS is three times more common in women than men, perhaps because the carpal tunnel itself may be narrower.
Reviewed by: Galal Elsayed, MD
Last reviewed/last updated: October 2023