The swollen tendons and their coverings cause friction within the narrow tunnel, or sheath, through which they pass. The result is pain at the base of the thumb. De Quervain's disease is one of the most common types of tendon-lining inflammation. Pain along the back of the thumb, directly over two thumb tendons, is common in cases of de Quervain's. Thumb motion may be difficult and painful, particularly when pinching or grasping objects.
Some people also experience swelling and pain on the side of the wrist at the base of the thumb.
The pain may increase with thumb and wrist motion. Some people feel pain if direct pressure is applied to the area. Overuse, a direct blow to the thumb, repetitive grasping and certain inflammatory conditions, such as rheumatoid arthritis, can all trigger the disease. Gardening, racquet sports and various workplace tasks are examples of activities that may aggravate the condition. Often, the cause is unknown.