De Quervain tenosynovitis (dih-kwer-VAIN ten-oh-sine-oh-VIE-tis) is a painful condition affecting the tendons on the thumb side of the wrist. If you have de Quervain tenosynovitis, you will probably feel pain when you turn your wrist, grasp anything or make a fist. Although the exact cause of de Quervain tenosynovitis isn't known, any activity that relies on repetitive hand or wrist movement — such as working in the garden, playing golf or racket sports, or lifting a baby — can make it worse.