Accessory neuropathy: Disease of the accessory nerve which is the eleventh cranial nerve. The accessory nerve supplies the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is in the front of the neck and turns the head. The trapezius muscle moves the scapula (the wingbone), turns the face to the opposite side, and helps pull the head back.

Damage to the accessory nerve can be confined to the accessory nerve or it may also involve the ninth and tenth cranial nerves which exit through the same opening (foramen) from the skull . Accessory neuropathy can sometimes occur and recur for unknown reasons. Most patients recover.

Paralysis of the accessory nerve prevents rotation of the head away from that side and causes drooping of the shoulder.