Numbness in hands: What causes this?

The most common cause of intermittent numbness in hands or fingers is carpal tunnel syndrome. These sensations often occur while holding a book or newspaper or while driving a vehicle. They may also be present on awakening from sleep.

The carpal tunnel is a narrow space on the palm side of your wrist. This tunnel protects a main nerve to your hand (median nerve) and several tendons that bend your fingers. Pressure placed on the nerve causes numbness in hands and fingers, as well as pain and eventually weakness — all typical signs and symptoms of carpal tunnel syndrome.

Pressure on the median nerve can result from anything that reduces space in the carpal tunnel — from bone spurs to the most common cause, which is swelling or thickening of the lining and lubricating layer (synovium) of the tendons in the carpal tunnel. The exact cause of such swelling usually can't be determined. But it may be associated with a variety of conditions and factors, such as diabetes, thyroid disorders, rheumatoid arthritis, fluid retention in pregnancy, and repetitive use or injury.

A doctor may make a diagnosis of carpal tunnel syndrome based on signs and symptoms and a physical examination. Treatment depends on the severity of the condition.