Dequervain’s tendinitis also called DeQuervain’s tendinosis or occurs when the tendons around the base of the thumb are irritated or constricted. The word “tendinitis” refers to a swelling of the tendons. Thickening of the tendons can cause pain and tenderness along the thumb side of the wrist. This is particularly noticeable when forming a fist, grasping or gripping things, or when turning the wrist.

Anatomy 
Two of the main tendons to the thumb pass through a tunnel (or series of pulleys) located on the thumb side of the wrist. Tendons are rope-like structures that attach muscle to bone. Tendons are covered by a slippery thin soft-tissue layer, called synovium. This layer allows the tendons to slide easily through the tunnel. Any thickening of the tendons restrains gliding of the tendons through the sheath. Movement of the thumb may cause pain at the thumb side of the wrist.

Causes 
DeQuervain’s tendinitis is caused when tendons on the thumb side of the wrist are swollen or irritated. The irritation causes the lining (synovium) around the tendon to swell, which changes the shape of the compartment. This makes it difficult for the tendons to move as they should. DeQuervain’s tendinitis is most common in middle-aged women. It can be seen in association with pregnancy. It may be found in inflammatory arthritis, such as rheumatoid arthritis. Tendinitis may be aggravated by overuse.

Symptoms

• Pain may be felt over the thumb side of the wrist. This is the main symptoms. The pain may appear either gradually or suddenly. Pain is felt in the wrist and can travel up the forearm or down the thumb. The pain is usually worse when the hand and thumb are in use. This is especially true when forcefully grasping objects or twisting the wrist.
• Swelling may be seen over the thumb side of the wrist. This swelling may occur together with a fluid-filled cyst in this region.
• A “catching” or “snapping” sensation may be felt when moving the thumb.
• Pain and swelling may make it difficult to move the thumb and wrist.