De Quervain's tenosynovitis is swelling and inflammation of the tendons and the tendon sheath on the thumb side of the wrist.

The exact cause of de Quervain's is not known. It may occur from injury to the wrist or tendon. Or it may occur as a result of activities that require repeated wrist and thumb movements, such as knitting, wringing clothes, or lifting heavy objects.

Symptoms may include swelling, a grating feeling in the wrist, and pain and weakness along the thumb, wrist, and forearm. Pain increases with activities such as lifting or pouring.

Initial treatment consists of rest, splinting, stretching, and medicines to reduce inflammation. Physiotherapy, a steroid injection, or surgery may sometimes be needed.