A myelin regenerator was a 24th century medical device used to regenerate the myelin sheath of a nerve.
In 2373, The Doctor used the myelin regenerator on Tom Paris after he was attacked by members of the Swarm species. (VOY: "The Swarm")
Later that year, Kathryn Janeway used this device on her arm after she was bitten by a macrovirus that had infested USS Voyager. (VOY: "Macrocosm")