What is the definition or description of: de Quervain's tenosynovitis?

Tendon sheath inflam. Named after swiss surgeon fritz de quervain in 1895 , it is an irritation of the sheath or tunnel that surrounds the extensor pollicis brevis and abductor pollicis longus tendons that function to move the thumb away from the hand.The tendons run in synovial sheaths that become inflamed and thereby cause pain. Microscopic evaluation indicates only a degenerative process of the tendon.
Inflammation. Tenosynovium is a sheath/tissue that surrounds many of our tendons. When this sheath gets inflammed we call it tenosynovitis. De quervain's is tenosynovitis of two tendons in the wrist just below the thumb (abductor pollicis longus and extensor pollicis brevis).