De Quervain’s tenosynovitis, also known as De Quervain's stenosing tenosynovitis, is tendonitis of the wrist. Tendonitis of the wrist is an irritation and swelling of the wrist tunnel that the tendons of the thumb pass through on the way into the hand. The most common symptom of De Quervain's is a pain over the tunnel in the wrist when pinching, grasping, or stretching the wrist toward the small finger. Sometimes a swelling can be felt over this inflamed tunnel.
De Quervain's (Say "duh-Kair-VAZ") syndrome or de Quervain's disease named after the Swiss surgeon Fritz de ‘Quervain, who identified it first in 1895. It’s an inflammation of the sheath or tunnel that surrounds two tendons that control the movement of the thumb. It’s caused by repetitive use of the thumb in combination with radial deviation of the wrist. (pinching, wringing, lifting, grasping, gardening, knitting). In this position the tendons of the EPB and the APL are pressed to the processus styloideus and when the movement is repeated frequently it can cause irritation of the tendons by friction. The tendons swell, the tunnel becomes too small.