What are hyperactive deep tendon reflexes?

See below: A DTR is a brisk contraction of a muscle in response to a sudden stretch induced by a sharp tap by a finger or rubber hammer on the tendon of insertion of the muscle. Absence of the reflex may be caused by damage to the muscle, peripheral nerve, nerve roots, or spinal cord at that level. A hyperactive reflex may indicate disease of the pyramidal tract above the level of the reflex arc being tested.